August 26, 2010

From Alimentary Pharmacology & Therapeutics

C. M. Lange; C. Sarrazin; S. Zeuzem

Posted: 08/25/2010; Alimentary Pharmacology & Therapeutics. 2010;32(1):14-28. © 2010 Blackwell Publishing

Abstract and Introduction

Abstract

Background Novel, directly acting anti-viral agents, also named 'specifically targeted anti-viral therapy for hepatitis C' (STAT-C) compounds, are currently under development.

Aim To review the potential of STAT-C agents which are currently under clinical development, with a focus on agents that target HCV proteins.

Methods Studies evaluating STAT-C compounds were identified by systematic literature search using PubMed as well as databases of abstracts presented in English at recent liver and gastroenterology congresses.

Results Numerous directly-acting anti-viral agents are currently under clinical phase I–III evaluation. Final results of phase II clinical trials evaluating the most advanced compounds telaprevir and boceprevir indicate that the addition of these NS3/4A protease inhibitors to pegylated interferon-alfa and ribavirin strongly improves the chance to achieve a SVR in treatment-naive HCV genotype 1 patient as well as in prior nonresponders and relapsers to standard therapy. Monotherapy with directly acting anti-virals is not suitable. NS5B polymerase inhibitors in general have a lower anti-viral efficacy than protease inhibitors.

Conclusions STAT-C compounds in addition to pegylated interferon-alfa and ribavirin can improve SVR rates at least in HCV genotype 1 patients. Future research needs to evaluate whether a SVR can be achieved by combination therapies of STAT-C compounds in interferon-free regimens.

Introduction

With the current standard of care, a combination therapy of pegylated interferon-alfa plus weight based ribavirin for 24 to 72 weeks, only half of all patients with chronic hepatitis C can be cured.[1–4] The chance to achieve a sustained virologic reponse (SVR) by such regimens differs significantly between HCV genotypes with SVR rates of 40–50% in patients infected with genotype 1, contrasted by SVR rates of approximately 80% in those infected with genotypes 2 or 3.[1–5] In addition, treatment with pegylated interferon-alfa and ribavirin is long (up to 72 weeks) and associated with numerous side effects like anaemia, flu-like symptoms or depression. In view of these facts, there is an urgent need for improved treatment strategies. The exploding knowledge of the HCV life cycle and of structural features of the HCV proteins has supported the development of many promising directly acting anti-viral agents, also named 'specifically targeted anti-viral therapy for hepatitis C' (STAT-C) compounds.[6–13] Figure 1 summarizes the HCV life cycle and potential targets for STAT-C.[11, 12] Many of these direct anti-virals are currently in phase I–III development and will significantly change treatment options for HCV infection in the near future. The most advanced compounds are telaprevir and boceprevir that are both inhibitors of the HCV NS3 protease and that have been shown to significantly enhance SVR rates in HCV genotype 1 patients, when applied in addition to pegylated interferon-alfa and ribavirin.[14–16] These and other STAT-C compounds will be described in this review with a focus on agents that were already evaluated in clinical trials (Table 1). Anti-virals targeting host proteins which are mandatory for HCV replication (e.g. nitazoxanide, celgosivir or DEBIO-025) are reviewed elsewhere.[17–21]


Figure 1.
The HCV replication complex. After clathrin-mediated endocytosis, fusion of HCV with cellular membranes, and uncoating the viral nucleocapsid, the single-stranded positive-sense RNA genome of the virus of approximately 9600 nucleotides is released into the cytoplasm to serve as a messenger RNA for the HCV polyprotein precursor. The HCV genome contains a single large open reading frame encoding for a polyprotein of approximately 3100 amino acids. The translated section of the HCV genome is flanked by the strongly conserved HCV 3′ and 5′ untranslated regions (UTR). The 5′ UTR is comprised of four highly structured domains forming the internal ribosome entry site (IRES), which is a virus-specific structure to initiate HCV mRNA translation. From the initially translated polyprotein, the structural HCV protein core (C) and envelope 1 and 2 (E1, E2); p7; and the six nonstructural HCV proteins NS2, NS3, NS4A, NS4B, NS5A and NS5B, are processed by both viral and host proteases. The core protein forms the viral nucleocapsid carrying E1 and E2, which are receptors for viral attachment and host cell entry. The tetraspanin protein CD81, claudin-1, occludine, scavenger receptor class B type 1 (SR-B1), the low-density lipoprotein (LDL) receptor, glycosaminoglycans and the dendritic cell-/lymph node-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN/L-SIGN) have been identified as putative ligands for E1 and E2.[83–86] The nonstructural proteins are mainly enzymes essential for the HCV life cycle. P7 is a small hydrophobic protein that oligomerises into a circular hexamer, most probably serving as an ion channel through the viral lipid membrane.[7, 87–91] NS2 and NS3 are viral proteases required for the procession of the HCV polyprotein. NS2 is a metalloproteinase that cleaves itself from the NS2/NS3 protein, leading to its own loss of function and to the release of the NS3 protein.[7, 90, 91] NS3 provides a serine protease activity and a helicase/NTPase activity. The serine protease domain comprises two β-barrels and four α-helices. The serine protease catalytic triad – histidine 57, asparagine 81 and serine 139 – is located in a small groove between the two β-barrels. NS3 forms a tight, noncovalent complex with its obligatory cofactor and enhancer NS4A, which is essential for proper protein folding. The NS3/4A protease cleaves the junctions between NS3/NS4A, NS4A/NS4B, NS4B/NS5A and NS5A/NS5B. Besides its essential role in protein processing, NS3 is integrated into the HCV RNA replication complex, supporting the unwinding of viral RNA by its helicase activity. NS4B and NS5B are involved in the organization of the HCV replication complex by interactions with lipid membranes, which lead to the formation of the so called membranous web.[11, 12, 69, 92] The membranous web comprises of rearranged intracellular lipid membranes derived from the endoplasmic reticulum. It provides the basis for the highly structured association of viral proteins and RNA, and of cellular proteins and cofactors within the replication complex. In addition, NS4B and NS5B are involved in transport of viral RNA within the replication complex.[11, 12, 69, 92] NS5B is an RNA-dependent RNA-polymerase which catalyses the synthesis of a complementary negative-strand RNA by using the positive-strand RNA genome as a template.[11, 12, 69] From this newly synthesized negative-strand RNA, numerous RNA strands of positive polarity are produced by NS5B activity which serve as templates for further replication and polyprotein translation. As a result of its poor fidelity leading to a high rate of errors in its RNA sequencing, numerous different isolates are generated during HCV replication in a given patient, termed HCV quasispecies. It is thought that as a result of the lack of proof-reading of the NS5B polymerase together with the high replication rate of HCV every possible mutation will be generated each day. Thus, NS5B is one key factor in the development of viral resistance during STAT-C therapies.
 
Compounds Targeting HCV Polyprotein Procession
 
NS3/4A Protease Inhibitors

The design of NS3/4A inhibitors is relatively difficult because the active site of the NS3/4A protease is located in a shallow groove between two β-barrels of the protease.[6, 7] Nevertheless, many NS3/4A protease inhibitors are under development, which in general provide a high anti-viral efficacy but a low genetic barrier to resistance. Protease inhibitors can be divided into two chemical classes, macrocyclic inhibitors and linear tetra-peptide α-ketoamid derivatives. NS3/4A protease inhibitors of both classes strongly inhibit HCV replication during monotherapy, but also frequently cause the selection of resistant mutants which may be followed by viral breakthrough.[13, 22] However, it was shown that the frequency of resistance development against protease inhibitors can be vastly reduced by the additional administration of pegylated interferon and ribavirin. The most advanced compounds are telaprevir and boceprevir that are currently under phase III evaluation and are expected to be approved in 2011/2012.

Ciluprevir (BILN 2061)

The first NS3/4A inhibitor applied in clinical studies was ciluprevir (BILN 2061), an orally bioavailable, peptidomimetic, macrocyclic drug binding noncovalently to the active centre of the enzyme.[23] Ciluprevir monotherapy was evaluated in a double-blind, placebo-controlled pilot study in treatment-naïve genotype 1 patients with compensated liver disease.[24] In this study, ciluprevir, administered twice daily for 2 days at doses ranging from 25 to 500 mg, led to a mean 2–3 log10 decrease of HCV RNA serum levels in most patients. Another study with equivalent design assessed the influence of the HCV genotype on treatment with this protease inhibitor. Compared with genotype 1 patients, the anti-viral activity of ciluprevir was less pronounced and more variable in patients infected with genotypes 2 or 3.[25] Although the development of ciluprevir was stopped because of serious cardiotoxicity observed in an animal model, these studies provided the proof-of-principle for successful suppression of HCV replication by NS3/4A inhibitors in patients with chronic hepatitis C.

Viral Resistance to Ciluprevir. As a result of the high replication rate of HCV and the poor fidelity of its RNA-dependent RNA polymerase, numerous variants (quasispecies) are continuously produced during HCV replication. Amongst them, variants carrying mutations altering the conformation of the binding sites of STAT-C compounds can develop. During treatment with specific anti-virals, these pre-existing drug-resistant variants have a fitness advantage and can be selected to become the dominant viral quasispecies. Many of these resistant mutants exhibit an attenuated replication fitness with the consequence that, after termination of exposure to specific anti-virals, the wild-type may again replace the resistant variants.[22, 26] Nevertheless, HCV quasispecies resistant to NS3/4A protease inhibitors or non-nucleoside polymerase inhibitors can be detected at very low levels in some patients who were never treated with specific anti-virals before.[27–29] The clinical relevance of these pre-existing mutants is not completely understood, although there is evidence that they may reduce the chance to achieve a SVR by therapies based on HCV protease or non-nucleoside polymerase inhibitors.

Exposure of genotype 1 replicon cells to ciluprevir and subsequent sequence analyses of the NS3 region have led to the identification of several mutations conferring ciluprevir-resistance: A156T, R155Q and D168V/A. These mutations result in a 357-fold, 24-fold and 144-fold reduced susceptibility to ciluprevir, respectively, compared with wild-type.[30–32] The A156T mutant confers varying levels of cross-resistance to ciluprevir, telaprevir and boceprevir. The A156T mutation causes a significantly reduced enzymatic function attenuating the HCV life cycle, which, however, can be overcome by additional mutations at P89L, Q86R or G162R.[30–32] No data are available on clinically selected resistance mutations after administration of ciluprevir in patients with chronic hepatitis C.

Telaprevir (VX-950)

Telaprevir is an orally bioavailable NS3 protease inhibitor which belongs to the α-ketoamids and binds the enzyme covalently but reversibly, with a half-life of 58 min of the enzyme-inhibitor complex. Currently, telaprevir is under phase III evaluation (ADVANCE- and ILLUMINATE-Study for treatment-naïve patients, REALIZE study for nonresponders).

Phase I Studies. Telaprevir Monotherapy Study A double-blind, randomized placebo-controlled phase Ib clinical trial evaluating telaprevir monotherapy over 14 days was performed in patients with chronic HCV genotype 1 infection.[33] In this study, anti-viral activity, safety, optimal dosage and pharmacokinetics were assessed in treatment-naïve patients, relapsers or nonresponders to standard treatment. Doses of telaprevir were 450 mg or 750 mg every 8 h or 1250 mg every 12 h. Telaprevir was well tolerated and led to a rapid decline of HCV RNA serum levels in all groups. The best results were obtained in the 750 mg telaprevir q8h dose group with a median reduction of HCV RNA of 4.4 log10 after 14 days of treatment, which is the basis for telaprevir-dosage in most of the following clinical trials. However, viral rebound because of selected mutants occurred in all patients after treatment completion and in some patients even during therapy. The selection of resistant mutants was more frequent in patients who received suboptimal doses.[22

Telaprevir/pegylated (peg) Interferon α-2a/ribavirin Combination Studies A second phase I study investigated the safety, viral kinetics and the development of telaprevir-resistant mutants of telaprevir monotherapy and in combination with pegIFN-α 2a in treatment-naïve genotype 1 patients.[34] Telaprevir dosage was 750 mg every 8 h after an initial loading dose of 1250 mg and it was administered either alone or in combination with pegIFN-α 2a in comparison to pegIFN-α 2a monotherapy. Treatment was given for 14 days and caused a median reduction of HCV RNA of 1.09 log10 in the pegIFN-α 2a/placebo group, of 3.99 log10 in the telaprevir/placebo group and of 5.49 log10 in the telaprevir/pegIFN-α 2a group at the end of therapy. As observed before, selection of telaprevir-resistant mutants occurred during telaprevir monotherapy. However, their frequency was significantly lower during combination therapy with pegIFN-α 2a and no viral breakthrough was seen during the combination therapy within 14 days.[34]

A parallel study evaluated the safety and efficacy of telaprevir (750 mg every 8 h) in combination with pegIFN-α 2a and weight-based ribavirin in treatment-naive genotype 1 patients for 28 days.[35] At the end of the 28-day treatment period, all patients had undetectable HCV RNA serum levels.

Phase II Studies. Telaprevir and peg Interferon with and without Ribavirin

Studies in treatment naïve patients (PROVE 1 and 2, C208, C209, C210) Larger phase II clinical trials (PROVE 1 and 2) in treatment naïve genotype 1 patients assessed whether with additional telaprevir to pegIFN-α 2a and ribavirin, overall treatment duration can be reduced and/or SVR rates be improved (Figures 2 and 3). PROVE 1 was conducted in the USA whereas PROVE 2 was conducted in Europe. In addition, a study comparing two vs. three times daily administration of telaprevir in combination with either pegylated interferon alfa 2a or 2b (C208) and studies in genotype 2, 3 and 4 infected patients were performed (C209, C210).


Figure 2.
Results of PROVE 1 (USA). Combination therapy of telaprevir (TVR) and pegIFN-α 2a + ribavirin in treatment-naive genotype 1 patients.
 
 
Figure 3.
Results of PROVE 2 (Europe). Combination therapy of telaprevir (TVR) and pegIFN-α 2a ± ribavirin in treatment-naive genotype 1 patients
 
In PROVE 1, telaprevir, pegIFN-α 2a and ribavirin were administered for 12 weeks in combination, followed by pegIFN-α 2a and ribavirin alone for 0 (n = 17), 12 (n = 79) or 36 (n = 79) weeks in comparison to standard treatment. SVR rates were 35%, 61% and 67%, respectively, compared to 41% with standard treatment. According to the study protocol, treatment was only stopped after 12 or 24 weeks when a rapid virological response (RVR) was achieved. Serious adverse effects led to premature treatment termination in 18% of all subjects treated with telaprevir in contrast to 4% of patients with standard-therapy. Most common adverse events were skin rash, anaemia and gastrointestinal disorders.[15]
 
The study design of PROVE 2 was similar to PROVE 1 with the main difference being that treatment termination after 12 or 24 weeks was independent of achieving an RVR and one treatment arm was ribavirin-free. The recently published final results showed SVR rates of 36%, 60% and 69% for patients treated with telaprevir plus pegIFN alone for 12 weeks (n = 78), telaprevir and pegIFN and ribavirin for 12 weeks (n = 82), and with telaprevir, pegIFN and ribavirin for 12 weeks followed by 12 weeks of pegIFN plus ribavirin alone (n = 81) respectively. The SVR rate achieved by standard treatment was 46%. However, the rate of relapse in the groups treated for 12 weeks was relatively high with 30% and 48% of all patients who were treated with and without ribavirin respectively. Two patients who discontinued treatment at day 60 and 65 experienced a late relapse 36 and 48 weeks after the end of treatment respectively.[14]

The results of PROVE 1 and 2 indicate that 12 weeks of triple therapy was too short because of the high rate of relapse after treatment completion. Moreover, ribavirin is necessary in therapies with telaprevir to achieve high SVR rates. However, 24 to 48 weeks of total therapy including 12 weeks of triple therapy with telaprevir in addition to standard treatment greatly improved SVR rates in treatment-naïve genotype 1 patients compared with the standard of care. The RVR during triple therapy is an important predictor for treatment success and can be applied for defining individualized treatment durations.

The most important side effects of telaprevir are rash, gastrointestinal disorders and anaemia. Although severe rash may require treatment discontinuation, moderate forms can be treated successfully with topical steroids. The median decline of blood haemoglobin concentration related to telaprevir was approximately 1 g/dL. As telaprevir was administered in most trials for only 12 weeks, the use of erythropoietin-analogues was rarely necessary.

C208 was a small study (n = 161) comparing three times daily 750 mg with two times daily 1125mg telaprevir combined with pegylated interferon alfa 2a or 2b, respectively, and ribavirin.[36] In all four treatment arms comparable SVR rates were observed (81–85%). These high overall SVR rates underline the potential of the triple therapy approach. They are explained in part by experienced study centres with very low discontinuation rates (5%) in comparison with the PROVE studies. In addition, in this study the response-guided therapy approach was investigated. Treatment duration was shortened to 24 weeks in patients who achieved a RVR, while the remaining patients received 48 weeks therapy. Between 80–83% of all patients treated with pegIFN-α 2a, and 67–69% of all patients treated with pegIFN-α 2b achieved an RVR and could therefore be treated for 24 weeks.

As the amino acid sequence of the NS3 protease domain varies significantly between HCV genotypes, protease inhibitors may have a different anti-viral efficacy in patients infected with different genotypes. Like ciluprevir, telaprevir alone or in combination with pegIFN and ribavirin was less effective in treatment-naïve patients infected with other genotypes than genotype 1. For HCV genotype 2, a somewhat weaker anti-viral activity in comparison with HCV genotype 1 was observed with a mean viral decline of 3.9 log10 IU/mL during 14 days of monotherapy with telaprevir. In genotype 3 and 4 infected patients, no significant anti-viral activity was detectable (0.5–0.9 log10 decline).[37, 38]

Studies in Nonresponders and Relapsers (PROVE 3) The PROVE 3 trial was conducted to determine SVR rates of treatment with telaprevir in combination with pegIFN-α and ribavirin in treatment-experienced patients (Figure 4). Telaprevir was administered in combination with pegIFN-α 2a with and without ribavirin for 12 to 24 weeks followed by pegIFN-α 2a and ribavirin alone for up to 24 weeks. Retreatment of previous nonresponders with 12 weeks of triple therapy followed by 12 weeks of standard treatment led to a SVR rate of 51% (69% relapser, 39% nonresponder), which is significantly higher compared with SVR rates achieved with the standard of care (14%). Retreatment of nonresponders with 24 weeks of triple therapy followed by 24 weeks of standard treatment led to a SVR rate of 53% (76% relapser, 38% nonresponder) and retreatment of nonresponders with 24 weeks of telaprevir and pegIFN-α 2a without ribavirin followed by 24 weeks of pegIFN-α 2a alone led to a SVR rate of only 24% (42% relapser, 11% nonresponder). The latter result indicates that ribavirin is required for a successful treatment of nonresponders with telaprevir. As in the PROVE 1 and 2 studies viral breakthrough was observed more frequently in patients infected with genotype 1a than in patients infected with genotype 1b.[39]


Figure 4.
Results of PROVE 3. Combination therapy of telaprevir (TVR) and pegIFN-α 2a ± ribavirin in HCV genotype 1 patients with prior nonresponse or relapse to standard treatment.
 
Phase III Studies. Design of Phase III Clinical Trials: Telaprevir with Pegylated Interferon-alfa and Ribavirin Phase III clinical trials evaluating telaprevir in combination with pegIFN-α and ribavirin have been initiated. The ADVANCE trial enrolled more than 1000 treatment-naïve HCV genotype 1 patients to evaluate 24 weeks of telaprevir-based therapy. Telaprevir was dosed at 750 mg every 8 h and given for 8 or 12 weeks in combination with pegIFN-α 2a and ribavirin followed by pegIFN-α 2a and ribavirin alone until treatment week 24. Patients who did not achieve an RVR were treated with pegIFN-α 2a and ribavirin until week 48. In the ILLUMINATE trial, telaprevir was given for 12 weeks in combination with pegIFN-α 2a and ribavirin followed by pegIFN-α 2a and ribavirin alone until treatment week 24 or 28. The aim of the ILLUMINATE trial is to assess whether treatment extension beyond 24 weeks of total therapy improves SVR rates in patients with RVR or EVR. The REALIZE study enrolled more than 650 patients with prior failure to standard treatment. PegIFN-α 2a and ribavirin were given for 48 weeks including 12 weeks of telaprevir at a dose of 750 mg every 8 h. In one treatment arm, telaprevir treatment was initiated after a 4 week lead-in phase of pegIFN-α 2a and ribavirin alone. SVR data of the ADVANCE, ILLUMINATE and REALIZE study are expected to be published in 2010.
 
Viral Resistance to Telaprevir To date, mutations conferring telaprevir-resistance have been identified at four positions, V36A/M/L, T54A, R155K/M/S/T and A156S//T,[22, 30, 31, 40] see Table 2 and Table 3 . The A156 mutation was shown by in vitro analyses in the replicon assay while the other mutations could only be detected in vivo by a clonal sequencing approach during telaprevir administration in patients with chronic hepatitis C. A detailed kinetic analysis of telaprevir-resistant variants was performed in genotype 1 patients during 14 days of telaprevir monotherapy and combination therapy with pegIFN-α 2a.[41] Telaprevir monotherapy initially led to a rapid HCV RNA decline in all patients as a result of a strong reduction in wild-type virus. In patients who developed a viral rebound during telaprevir monotherapy, mainly the single mutation variants R155K/T and A156/T were uncovered by wild-type reduction and became dominant after day 8. These single mutation variants were selected from pre-existing quasispecies. During the viral rebound phase these variants typically were replaced by highly resistant double-mutation variants (e.g., V36M/A +R155K/T). The combination of telaprevir and pegIFN-α 2a was sufficient to inhibit the breakthrough of resistant mutations in a 14-day study. It is important to note that after up to 3 years after telaprevir treatment low to medium levels of V36 and R155 variants were still observed in single patients.[42] Another study modelling the dynamics of wild type HCV genotype 1 in patients treated with telaprevir with and without pegylated interferon-alfa and ribavirin showed a first and second phase reduction in virus decline which was up to 10-fold stronger than reported for the standard of care.[43]

As shown for other NS3/4A protease inhibitors as well (e.g. ITMN-191), the genetic barrier to telaprevir resistance differs significantly between HCV subtypes. In all clinical studies of telaprevir alone or in combination with pegIFN-α and ribavirin, viral resistance and breakthrough occurred much more frequently in patients infected with HCV genotype 1a compared with genotype 1b. This difference was shown to result from nucleotide differences at position 155 in HCV subtype 1a (aga, encodes R) vs. 1b (cga, also encodes R). The mutation most frequently associated with resistance to telaprevir is R155K; changing R to K at position 155 requires 1 nucleotide change in HCV subtype 1a and 2 nucleotide changes in subtype 1b isolates.[44]

Boceprevir (SCH 503034)

Boceprevir is another novel peptidomimetic orally bioavailable α-ketoamid HCV protease inhibitor that forms a covalent but reversible complex with the NS3 protein.[45] Like telaprevir, boceprevir is currently in phase III evaluation.

Phase I Studies. Boceprevir Monotherapy Study An initial phase I trial evaluated safety, tolerability and anti-viral efficacy of boceprevir monotherapy (100 to 400 mg daily) in HCV genotype 1 patients with prior failure to standard therapy.[46] After the 14-day treatment period, a mean log10 reduction in HCV RNA load of 2.06 was achieved in patients treated with 400 mg boceprevir daily. Boceprevir was well tolerated at all doses without significant adverse effects. However, viral breakthrough with selection of resistant variants occurred in some patients with a frequency depending on boceprevir dosage.[47]

Boceprevir/peg Interferon α-2b Combination Study A subsequent phase Ib study evaluated the combination of boceprevir and pegIFN-α 2b in HCV genotype 1-infected nonresponders to standard therapy.[48] In this randomized, double-blind crossover study, boceprevir was administered at doses of 200 or 400 mg every 8 h either alone for 7 days or in combination with pegIFN-α 2b for 14 days in comparison to 14 days of pegIFN-α 2b monotherapy. As HCV genotype 1 nonresponders to standard treatment are heterogeneous, the study design intended each patient to receive boceprevir alone, in combination with pegIFN-α 2b and pegIFN-α 2b alone with washout-periods in between in a randomized crossover sequence. Mean maximum reductions in HCV RNA load were 2.45 and 2.88 log10 for boceprevir 200 mg and 400 mg plus pegIFN-α 2b, 1.08 and 1.61 log10 for boceprevir monotherapy and 1.08 and 1.26 log10 for pegIFN-α 2b monotherapy. Boceprevir was well-tolerated alone and in combination with pegIFN-α 2b. Viral breakthrough resulting from selection of pre-existing resistant mutants was observed in some patients, in particular during boceprevir monotherapy.[49]

Phase II Studies. Boceprevir and peg Interferon with and without Ribavirin

Treatment Naïve Phase II Study (SPRINT-1) The aim of the SPRINT 1 trial was to investigate safety, tolerability and anti-viral efficacy of boceprevir (800 mg three times a day) in combination with pegIFN-α 2b and ribavirin in treatment-naïve HCV genotype 1 patients.[16] Treatment with boceprevir in combination with pegIFN-α 2b and ribavirin was either performed continuously for 28 or 48 weeks or for 24 or 44 weeks after a previous 4-week lead-in phase of pegIFN-α 2b and ribavirin alone. The lead-in design was chosen to determine a potential benefit of pre-treatment with pegIFN-α 2b and ribavirin on avoiding resistance development. The control group was treated with pegIFN-α 2b and ribavirin for 48 weeks. SVR rates after 28 weeks of triple treatment were 54% and 56% after 24 weeks with an additional 4 weeks of pre-treatment lead in with pegIFN-α2 and ribavirin (Figure 5). SVR rates after 48 weeks of triple treatment were 67% and 75% after 44 weeks with an additional 4 weeks of pre-treatment lead in with pegIFN-α 2b and ribavirin. After 4 weeks triple therapy with boceprevir, pegIFN and ribavirin 38% of patients achieved an RVR. The most common side-effects related to boceprevir were anaemia, nausea, vomiting and dysgeusia. In general, SPRINT-1 has proven a higher anti-viral efficacy of combination therapy with boceprevir in comparison to the standard of care with slightly better results after a 4 week lead-in phase. However, RVR rates of only 38% during boceprevir triple therapy indicate that boceprevir is potentially less potent than telaprevir which, during triple therapy with pegIFN-α 2b, lead to an RVR rate of approximately 70%.


Figure 5.
Results of SPRINT-1. Combination therapy of boceprevir and pegIFN-α 2b + ribavirin (RBV) in treatment-naive genotype 1 patients.
 
Studies in Nonresponders and Relapsers In a complex study of HCV genotype 1 nonresponders, the addition of boceprevir to pegIFN-α 2b and ribavirin resulted in only slightly increased SVR rates compared with standard treatment (14% vs. 2%).[50]
 
Design of Phase III Studies. A phase III clinical trial (SPRINT-2) evaluating boceprevir in treatment-naïve patients was initiated recently and has enrolled more than 1000 patients. Equivalent to the SPRINT-1 study design, patients receive 800 mg boceprevir three times daily in combination with pegIFN-α 2b and weight based ribavirin for 28 or 48 weeks. RESPOND-2 evaluates boceprevir in combination with pegIFN-α 2b and ribavirin at the same doses but for 36 and 48 weeks in relapsers and nonresponders. In all investigational arms a lead-in strategy with pegIFN-α 2b and ribavirin is followed.

Viral Resistance to Boceprevir. In the replicon system, mutations at three positions conferring boceprevir resistance were discovered (Table 3). T54A, A156S and V170A confer low level resistance to boceprevir whereas A156T that also confers telaprevir and ciluprevir resistance exhibited greater levels of resistance.[26] In patients with chronic hepatitis C three additional mutations were detected during boceprevir monotherapy (V36G/M/A, V55A, R155K).[47] In a number of these patients one year and in single patients even 4 years after the end of boceprevir treatment still resistant variants were detected in the HCV quasispecies by clonal sequence analysis.[51] However, an additional study revealed that the anti-viral activity of boceprevir was not impaired in patients who were treated with boceprevir with and without pegIFN-α before.[49]

Other NS3 Protease Inhibitors

Other NS3 protease inhibitors are currently in phase 1–2 development (R7227/ITMN191, MK7009, BI201335, TMC435350, SCH900518, BMS-650032, PHX1766, ACH-1625).[13, 52, 53] In general, they exhibit a high anti-viral activity in HCV genotype 1 patients, comparable with telaprevir and boceprevir (Figure 6). Triple therapy studies for a number of compounds have been initiated and confirm that resistance development is significantly reduced by combination with pegylated interferon and ribavirin. Whereas linear tetrapeptide and macrocyclic inhibitors do not differ in general with respect to their anti-viral activity, their resistance profile differs significantly. However, R155 is an overlapping position for resistance and different mutations at this amino acid site within the NS3 protease confer resistance to all protease inhibitors which are currently in advanced clinical development.[13]


Figure 6.
Anti-viral activity of NS3/4A protease inhibitors during monotherapy for 3–14 days (modified from [13]).
 
NS4A Inhibitors
 
ACH-806. NS4A is a crucial cofactor of NS3, mandatory for proper folding of the protease and capable to enhance the enzymatic activity of NS3 manifold. ACH-806 targets NS4A and therefore inhibits the NS3/4A protease by a different mechanism than peptidomimetic NS3 inhibitors. ACH-806 binds to newly synthesized NS4A molecules, which leads to the blockade of their assembly with NS3 proteins. A phase Ib trial in HCV genotype 1-infected patients demonstrated that ACH-806 has a significant inhibitory impact on HCV replication.[54] Although the development of ACH-806 was halted as a result of reversible serum creatinine elevations, the concept of NS4A inhibition was proven. Importantly, no cross-resistance between ACH-806 and peptidomimetic NS3/4A protease inhibitors was observed in vitro.[55, 56] Novel NS4A inhibitors (e.g. ACH-1095) are currently under preclinical development.

Compounds Targeting HCV Replication
 
NS5B Polymerase Inhibitors

NS5B RNA polymerase inhibitors can be divided into two distinct categories. Nucleoside analogue inhibitors (NIs) like valopicitabine (NM283), R7128, R1626, PSI-7851 or IDX184 mimic the natural substrates of the polymerase and are incorporated into the growing RNA chain, thus causing direct chain termination by tackling the active site of NS5B.[29, 57–67] As the active centre of NS5B is a highly conserved region of the HCV genome, NIs are potentially effective against different genotypes, in contrast to NS3/4A inhibitors. Moreover, single amino acid substitutions in every position of the active centre may result in loss of function. Thus, there is a relatively high genetic barrier in the development of resistances to NIs.

In contrast to NIs, the heterogeneous class of non-nucleoside inhibitors (NNIs) bind to different allosteric enzyme sites, which results in conformational protein change before the elongation complex is formed.[68] To inhibit NS5B allostericaly, a high chemical affinity of the compound to the enzyme is required. NS5B is structurally organized in a characteristic 'right hand motif', containing finger, palm and thumb domains, and offers at least four NNI-binding sites, a benzimidazole-(thumb 1)-, thiophene-(thumb 2)-, benzothiadiazine-(palm 1)- and benzofuran-(palm 2)-binding site.[68, 69] Theoretically, NNIs targeting different binding sites can be used in combination or in sequence to manage the development of resistance. As NNIs bind distantly to the active centre of NS5B, their application results more frequently in resistance development than during treatment with NIs. In addition, mutations at the NNI-binding sites do not necessarily lead to impaired function of the enzyme.

Nucleoside Analogues

Valopicitabine (NM283, 2′-C-methylcytidine/NM107) was the first nucleoside inhibitor investigated in patients with chronic hepatitis C. Anti-viral activity of valopicitabine was low.[70] The clinical development of valopicitabine was stopped because of gastrointestinal side effects and an insufficient risk/benefit profile.

The second nucleoside inhibitor investigated in patients with chronic hepatitis C was R1626 (4′-azidocytidine/PSI-6130). A phase 1 study showed a high anti-viral activity at high doses of R1626 in patients infected with HCV genotype 1.[63–65] No viral breakthrough with selection of resistant variants was reported from monotherapy or combination studies with pegylated interferon ± ribavirin. However, severe lymphopenia and infectious disease adverse events led to the stop of R1626 development.

R7128 is another nucleoside polymerase inhibitor with potent anti-viral activity during monotherapy in HCV genotype 1 patients. Currently, R7128 is investigated in phase 2 clinical trials in HCV genotype 1, 2 and 3 infected patients in combination with pegylated interferon and ribavirin.[59] Both during monotherapy and combination therapy with pegylated interferon and ribavirin, no resistance development against R7128 was observed.

Other nucleoside analogue inhibitors of the NS5B polymerase (PSI-7851 and IDX184) are evaluated in phase 1 clinical trials in patients with chronic hepatitis C and many compounds are under preclinical development.[13] For a summary of anti-viral activities of nucleoside polymerase inhibitors see Figure 7.


Figure 7.
Anti-viral activity of nucleoside analogue NS5B polymerase inhibitors during monotherapy for 3–14 days (modified from [13]).
 
Non-nucleoside Analogues
 
NNI-site 1 Inhibitors (Thumb 1/benzimidazole Site). BILB1941, BI207127 and MK-3281 are NNI-site 1 inhibitors which have been investigated in clinical phase 1 trials and exhibit low to medium anti-viral activities.[13, 71, 72] No selection of resistant variants and viral breakthrough has been observed during 5 days of treatment with BILB1941 or BI207127.

NNI-site 2 Inhibitors (Thumb 2/thiophene Site). Filibuvir (PF-00868554) is a NNI-site 2 inhibitor with medium anti-viral activity in a phase 1 study. In a subsequent trial viral breakthrough was observed in 5 of 26 patients during combination therapy with pegIFN-α 2a and ribavirin for 4 weeks.[72]

Other NNI-site 2 inhibitors which were evaluated in phase 1 trials are VCH-759, VCH-916 and VCH-222, their anti-viral efficacy is shown in Figure 8.[13, 73] Like during treatment with filibuvir, VCH-759 and VCH-916 application resulted in viral breakthroughs with selection of resistant variants, indicating a low genetic barrier to resistance of these agents.


Figure 8.
Anti-viral activity of non-nucleoside analogue NS5B polymerase inhibitors during monotherapy for 3–14 days (modified from [13]).
 
NNI-site 3 Inhibitors (Palm 1/benzothiadiazine Site). ANA598 is a NNI-site 3 inhibitor which displayed anti-viral activity during treatment of HCV genotype 1 infected patients. No viral breakthrough was observed during a short term monotherapy trial.[74]
 
NNI-site 4 Inhibitors (Palm 2/benzofuran Site). Monotherapy with the NNI-site 4 inhibitor HCV-796 showed low anti-viral activity in HCV genotype 1 infected patients and resulted in selection of resistant variants and viral breakthrough in several patients.[75, 76] GS-9190 displays a low anti-viral activity in a clinical study and variants conferring resistance were identified in the beta-hairpin of the polymerase.

An overview of the anti-viral activities of non-nucleoside polymerase inhibitors in monotherapy studies is shown in Figure 8.

NS5A Inhibitors

In a single ascending dose study it was shown that inhibition of the NS5A protein with BMS-790052 leads to a sharp initial decline of HCV RNA concentrations.[77] BMS-790052 binds to domain I of the NS5A protein, which was shown to be important for regulation of HCV replication. No clinical data on resistance to this class of drugs have been presented yet and results of multiple dose and combination therapy studies have to be awaited.

NS4B Inhibitors

NS4B is a hydrophobic protein mandatory for the formation of the membranous web of the HCV replication complex. Moreover, NS4B displays RNA-binding properties which may be crucial in HCV RNA procession and replication. In vitro, inhibition of NS4B by small molecular compounds has been shown to compromise HCV replication significantly.[78]

Combination Therapies of Specific Anti-virals

It is a fundamental question whether SVR can be achieved by combination therapies of different STAT-C compounds without pegIFN-α and ribavirin. A first clinical trial (INFORM-1 study) evaluated the combination of a polymerase inhibitor (R7128) and a NS3 inhibitor (R7227/ITMN191). In this proof-of-principle study, patients were treated with both compounds for up to 2 weeks. HCV RNA concentrations decreased up to 5.2 log10 IU/mL, no viral break-through was observed, and HCV RNA was undetectable at the end of dosing in up to 63% of treatment-naïve patients.[79] Future clinical trials need to address whether a long-term suppression of HCV replication or even SVR can be achieved with such direct anti-viral combination therapies. Currently, combination studies with several compounds are conducted (R7128 + R7227, VX-950 + VCH222, BMS790052 + BMS650032, BI201335 + BI207127).

Conclusions
 
Numerous directly acting anti-viral agents are currently under clinical phase I-III evaluation. Results of phase II clinical trials evaluating the most advanced compounds telaprevir and boceprevir indicate that the addition of these NS3/4A protease inhibitors to pegylated interferon-alfa and ribavirin substantially improves the chance to achieve a SVR in treatment-naive HCV genotype 1 patients as well as in prior nonresponders and relapsers to standard therapy. In addition, at least during treatment with telaprevir-based regimens, overall treatment durations can be shortened significantly.

Results of the milestone studies PROVE 1 and 2 indicate that 12 weeks of telaprevir-based triple therapy is too short because of the high rate of relapse after treatment completion. Moreover, ribavirin is necessary in therapies with telaprevir to achieve high SVR rates. However, 24 to 48 weeks of total therapy including 12 weeks of triple therapy with telaprevir in addition to standard treatment greatly improved SVR rates in treatment-naïve genotype 1 patients compared with the standard of care. The RVR during triple therapy is an important predictor for treatment success and can be applied for defining individualized treatment durations. Important side effects of telaprevir are, as observed during treatment with other protease inhibitors as well, anaemia, rash and gastrointestinal disorders. The SPRINT-1 trial demonstrated that SVR rates in treatment-naïve HCV genotype 1 patients can be enhanced by the addition of boceprevir to standard treatment as well. However, the lower anti-viral efficacy of boceprevir compared with telaprevir may require longer durations of boceprevir application.

PROVE 3 has shown that telaprevir is also highly effective in the treatment of prior nonresponders or relapsers infected with HCV genotype 1. In contrast, addition of boceprevir to standard treatment only revealed a minor impact on SVR rates in nonresponders, but further trials are awaited. In addition to telaprevir and boceprevir, many NS3/4A inhibitors with promising anti-viral activities are currently investigated in phase I and II trials.

Compared with NS3/4A protease inhibitors, most HCV polymerase inhibitors display a lower anti-viral activity during monotherapy. SVR data of triple therapies containing NS5B inhibitors need to be awaited. However, some polymerase inhibitors are equally effective against different HCV genotypes whereas it was shown that protease inhibitors such as telaprevir are less potent in other genotypes than HCV genotype 1. In addition, NS5B inhibitors at least of the nucleoside analogue family display a high genetic barrier to resistance.

Although it can be vastly reduced by addition of pegylated interferon-alfa and ribavirin, resistance development to directly acting anti-viral agents has to be kept in mind. R155 is the overlapping mutation conferring resistance to all clinically yet evaluated protease inhibitors. Although resistance against polymerase inhibitors needs to be better characterized, it is evident that their resistance profiles differ from those of protease inhibitors. Combination of different classes of STAT-C agents may therefore help to overcome limitations of resistance development. The impact of recently discovered polymorphisms near the IL28B gene on resistance development and SVR rates during STAT-C regimens needs to be characterized in future studies.[80–82]

A pivotal trial evidenced an additive anti-viral efficacy of the polymerase inhibitor R7128 in combination with the protease inhibitor ITMN-191 in an interferon- and ribavirin-free regimen. Whether SVR can be achieved with such interferon-free regimens needs to be addressed in future trials.

In conclusion, STAT-C compounds in addition to pegylated interferon-alfa and ribavirin are capable to improve SVR rates at least in HCV genotype 1 patients and will therefore be included in future treatment recommendations and guidelines.

References

1.Fried MW, Shiffman ML, Reddy KR, et al. Peginterferon alfa-2a plus ribavirin for chronic hepatitis C virus infection. N Engl J Med 2002; 347: 975–82.

2.Manns MP, McHutchison JG, Gordon SC, et al. Peginterferon alfa-2b plus ribavirin compared with interferon alfa-2b plus ribavirin for initial treatment of chronic hepatitis C: a randomised trial. Lancet 2001; 358: 958–65.

3.McHutchison JG, Gordon SC, Schiff ER, et al. Interferon alfa-2b alone or in combination with ribavirin as initial treatment for chronic hepatitis C. Hepatitis Interventional Therapy Group. N Engl J Med 1998; 339: 1485–92.

4.Zeuzem S, Hultcrantz R, Bourliere M, et al. Peginterferon alfa-2b plus ribavirin for treatment of chronic hepatitis C in previously untreated patients infected with HCV genotypes 2 or 3. J Hepatol 2004; 40: 993–9.

5.Hadziyannis SJ, Sette H, Jr, Morgan TR, et al. Peginterferon-alpha2a and ribavirin combination therapy in chronic hepatitis C: a randomized study of treatment duration and ribavirin dose. Ann Intern Med 2004; 140: 346–55.

6.Kim JL, Morgenstern KA, Lin C, et al. Crystal structure of the hepatitis C virus NS3 protease domain complexed with a synthetic NS4A cofactor peptide. Cell 1996; 87: 343–55.

7.Kim JL, Morgenstern KA, Griffith JP, et al. Hepatitis C virus NS3 RNA helicase domain with a bound oligonucleotide: the crystal structure provides insights into the mode of unwinding. Structure 1998; 6: 89–100.

8.Lindenbach BD, Evans MJ, Syder AJ, et al. Complete replication of hepatitis C virus in cell culture. Science 2005; 309: 623–6.

9.Lohmann V, Korner F, Koch J, Herian U, Theilmann L, Bartenschlager R. Replication of subgenomic hepatitis C virus RNAs in a hepatoma cell line. Science 1999; 285: 110–3.

10.Wakita T, Pietschmann T, Kato T, et al. Production of infectious hepatitis C virus in tissue culture from a cloned viral genome. Nat Med 2005; 11: 791–6.

11.Bartenschlager R, Frese M, Pietschmann T. Novel insights into hepatitis C virus replication and persistence. Adv Virus Res 2004; 63: 71–180.

12.Moradpour D, Penin F, Rice CM. Replication of hepatitis C virus. Nat Rev Microbiol 2007; 5: 453–63.

13.Sarrazin C, Zeuzem S. Resistance to Direct Antiviral Agents in Patients With Hepatitis C Virus Infection. Gastroenterology 2009; 138: 447–62.

14.Hezode C, Forestier N, Dusheiko G, et al. Telaprevir and peginterferon with or without ribavirin for chronic HCV infection. N Engl J Med 2009; 360: 1839–50.

15.McHutchison JG, Everson GT, Gordon SC, et al. Telaprevir with peginterferon and ribavirin for chronic HCV genotype 1 infection. N Engl J Med 2009; 360: 1827–38.

16.Kwo P, Lawitz E, McCone J, et al. HCV SPRINT-1 final results: SVR 24 from a phase 2 study of boceprevir plus peginterferon alfa-2b/ribavirin in treatmentnaive subjects with genotype-1 chronic hepatitis C. J Hepatol 2009; 50(Suppl. 1): 4.

17.Flisiak R, Horban A, Gallay P, et al. The cyclophilin inhibitor Debio-025 shows potent anti-hepatitis C effect in patients coinfected with hepatitis C and human immunodeficiency virus. Hepatology 2008; 47: 817–26.

18.Khattab MA. Targeting host factors: a novel rationale for the management of hepatitis C virus. World J Gastroenterol 2009; 15: 3472–9.

19.Rossignol JF, Kabil SM, El-Gohary Y, Keeffe EB. Randomized controlled trial of nitazoxanide-peginterferon-ribavirin, nitazoxanide-peginterferon and peginterferon-ribavirin in the treatment of patients with chronic hepatitis C genotype 4. J Hepatol 2008; 48: 30.

20.Rossignol JF, Elfert A, Keeffe EB. Evaluation of a 4 week lead-in phase with nitazoxanide prior to nitazoxanide+peginterferon in treating chronic hepatitis C. J Hepatol 2008; 48: 311.

21.Schinazi RF, Bassit L, Gavegnano C. HCV drug discovery aimed at viral eradication. J Viral Hepat 2010; 17: 77– 90.

22.Sarrazin C, Kieffer TL, Bartels D, et al. Dynamic hepatitis C virus genotypic and phenotypic changes in patients treated with the protease inhibitor telaprevir. Gastroenterology 2007; 132: 1767–77.

23.Lamarre D, Anderson PC, Bailey M, et al. An NS3 protease inhibitor with antiviral effects in humans infected with hepatitis C virus. Nature 2003; 426: 186–9.

24.Hinrichsen H, Benhamou Y, Wedemeyer H, et al. Short-term antiviral efficacy of BILN 2061, a hepatitis C virus serine protease inhibitor, in hepatitis C genotype 1 patients. Gastroenterology 2004; 127: 1347–55.

25.Reiser M, Hinrichsen H, Benhamou Y, et al. Antiviral efficacy of NS3-serine protease inhibitor BILN-2061 in patients with chronic genotype 2 and 3 hepatitis C. Hepatology 2005; 41: 832–5.

26.Tong X, Chase R, Skelton A, Chen T, Wright-Minogue J, Malcolm BA. Identification and analysis of fitness of resistance mutations against the HCV protease inhibitor SCH 503034. Antiviral Res 2006; 70: 28–38.

27.Gaudieri S, Rauch A, Pfafferott K, et al. Hepatitis C virus drug resistance and immune-driven adaptations: relevance to new antiviral therapy. Hepatology 2009; 49: 1069–82.

28.Kuntzen T, Timm J, Berical A, et al. Naturally occurring dominant resistance mutations to hepatitis C virus protease and polymerase inhibitors in treatmentnaive patients. Hepatology 2008; 48: 1769–78.

29.Le Pogam S, Seshaadri A, Kang H, et al. Low level of resistance, low viral fitness and absence of resistance mutations at baseline quasispecies may contribute to high barrier to R1626 resistance in vivo. J Hepatol 2008; 48: 10A.

30.Lin C, Gates CA, Rao BG, et al. In vitro studies of cross-resistance mutations against two hepatitis C virus serine protease inhibitors, VX-950 and BILN 2061. J Biol Chem 2005; 280: 36784–91.

31.Lin K, Kwong AD, Lin C. Combination of a hepatitis C virus NS3-NS4A protease inhibitor and alpha interferon synergistically inhibits viral RNA replication and facilitates viral RNA clearance in replicon cells. Antimicrob Agents Chemother 2004; 48: 4784–92.

32.Lu L, Pilot-Matias TJ, Stewart KD, et al. Mutations conferring resistance to a potent hepatitis C virus serine protease inhibitor in vitro. Antimicrob Agents Chemother 2004; 48: 2260–6.

33.Reesink HW, Zeuzem S, Weegink CJ, et al. Rapid decline of viral RNA in hepatitis C patients treated with VX-950: a phase Ib, placebo-controlled, randomized study. Gastroenterology 2006; 131: 997–1002.

34.Forestier N, Reesink HW, Weegink CJ, et al. Antiviral activity of telaprevir (VX-950) and peginterferon alfa-2a in patients with hepatitis C. Hepatology 2007; 46: 640–8.

35.Lawitz E, Rodriguez-Torres M, Muir AJ, et al. Antiviral effects and safety of telaprevir, peginterferon alfa-2a, and ribavirin for 28 days in hepatitis C patients. J Hepatol 2008; 49: 163–9.

36.Marcellin P, Forns X, Goeser T, et al. Virological analysis of patients receiving telaprevir administered q8h or q12h with peginterferon-alfa-2a or -alfa2b and ribavirin in treatment-naive patients with genotype 1 hepatitis C: study C208. Hepatology 2009; 50(Suppl 1): 395.

37.Benhamou Y, Moussalli J, Ratziu V, et al. Results of a prove of concept study (C210) of telaprevir monotherapy and in combination with peginterferon alfa-2a and ribavirin in treatment-naive genotype 4 HCV patients. J Hepatol 2009; 50(Suppl .1): 6.

38.Foster GR, Hezode C, Bronowicki JP, et al. Activity of telaprevir alone or in combination with peginterferon alfa-2a and ribavirin in treatment-naive genotype 2 and 3 hepatitis-C patients: interim results of study C209. J Hepatol 2009; 50(Suppl .1): 22.

39.McHutchison JG, Manns MP, Muir AJ, et al. Telaprevir for previously treated chronic HCV infection. N Engl J Med 2010; 362: 1292–303.

40.Lin K, Perni RB, Kwong AD, Lin C. VX-950, a novel hepatitis C virus (HCV) NS3-4A protease inhibitor, exhibits potent antiviral activities in HCv replicon cells. Antimicrob Agents Chemother 2006; 50: 1813–22.

41.Kieffer TL, Sarrazin C, Miller JS, et al. Telaprevir and pegylated interferonalpha-2a inhibit wild-type and resistant genotype 1 hepatitis C virus replication in patients. Hepatology 2007; 46: 631–9.

42.Forestier N, Susser S, Welker MW, Karey U, Zeuzem S, Sarrazin C. Long term follow-up of patients previously treated with telaprevir. Hepatology 2008; 48(Suppl .1): 760.

43.Adiwijaya BS, Hare B, Caron PR, et al. Rapid decrease of wild-type hepatitis C virus on telaprevir treatment. Antivir Ther 2009; 14: 591–5.

44.McCown MF, Rajyaguru S, Kular S, Cammack N, Najera I. GT-1a or GT-1b subtype-specific resistance profiles for hepatitis C virus inhibitors telaprevir and HCV-796. Antimicrob Agents Chemother 2009; 53: 2129–32.

45.Malcolm BA, Liu R, Lahser F, et al. SCH 503034, a mechanism-based inhibitor of hepatitis C virus NS3 protease, suppresses polyprotein maturation and enhances the antiviral activity of alpha interferon in replicon cells. Antimicrob Agents Chemother 2006; 50: 1013–20.

46.Zeuzem S, Sarrazin C, Wagner F, et al. Antiviral activity of SCH 503034, a HCV protease inhibitor, administered as monotherapy in hepatitis C genotype 1 (HCV-1) patients refractory to pegylated interferon (PEG-IFN-alpha). Hepatology 2005; 42: 276A.

47.Susser S, Welsch C, Wang Y, et al. Characterization of resistance to the protease inhibitor boceprevir in hepatitis C virusinfected patients. Hepatology 2009; 50: 1709–18.

48.Sarrazin C, Rouzier R, Wagner F, et al. SCH 503034, a novel hepatitis C virus protease inhibitor, plus pegylated interferon alpha-2b for genotype 1 nonresponders. Gastroenterology 2007; 132: 1270–8.

49.Vermehren J, Susser S, Karey U, Forestier N, et al. Clonal analysis of mutations selected in the NS3 protease domain of genotype 1 non-responders sequentially treated with boceprevir (SCH503034) and/or pegylated interferon-alfa-2b (peg-IFN-a-2b). Hepatology 2009; 50(Suppl .4): 1040.

50.Schiff E, Poordard F, Jacobson I, et al. Boceprevir combination therapy in null responders: response dependent on interferon responsiveness. J Hepatol 2008; 48(Suppl .2): 46.

51.Susser S, Forestier N, Welker MW, et al. Detection of resistant variants in the hepatitis C virus NS3 protease gene by clonal sequencing at long-term follow-up in patients treated with boceprevir. J Hepatol 2009; 50(Suppl 1): 7.

52.Reesink HW, Fanning GC, Farha KA, et al. Rapid HCV-RNA decline with once daily TMC435: a phase I study in healthy volunteers and hepatitis C patients. Gastroenterology 2010; 138: 913–21.

53.Forestier N, Larrey D, Guyader D, et al. Treatment of chronic hepatitis C virus (HCV) genotype 1 patients with the NS3/4A protease inhibitor ITMN-191 leads to rapid reductions in plasma HCV RNA: results of a phase 1b multiple ascending dose study. Hepatology 2008; 48(Suppl): 1132.

54.Pottage JC, Lawitz E, Mazur D, et al. Short-term antiviral activity and safety of ACH-806, an NS4A antagonist, in HCV genotype 1 infected individuals. J Hepatol 2007; 46: 294–5.

55.Wyles DL, Kaihara KA, Schooley RT. Synergy of a hepatitis C virus (HCV) NS4A antagonist in combination with HCV protease and polymerase inhibitors. Antimicrob Agents Chemother 2008; 52: 1862–4.

56.Yang W, Zhao Y, Fabrycki J, et al. Selection of replicon variants resistant to ACH-806, a novel hepatitis C virus inhibitor with no cross-resistance to NS3 protease and NS5B polymerase inhibitors. Antimicrob Agents Chemother 2008; 52: 2043–52.

57.Ali S, Leveque V, Le Pogam S, et al. Selected replicon variants with low-level in vitro resistance to the hepatitis C virus NS5B polymerase inhibitor PSI-6130 lack cross-resistance with R1479. Antimicrob Agents Chemother 2008; 52: 4356–69.

58.Klumpp K, Leveque V, Le Pogam S, et al. The novel nucleoside analog R1479 (4′-azidocytidine) is a potent inhibitor of NS5B-dependent RNA synthesis and hepatitis C virus replication in cell culture. J Biol Chem 2006; 281: 3793–9.

59.Lalezari J, Gane J, Rodriguez-Torres M, et al. Potent antiviral activity of the HCV nucleoside polymerase inhibitor R7128 with peg-IFN and ribavirin: interim results of R7128 500mg bid for 28 days. J Hepatol 2008; 48: 29.

60.Le Pogam S, Jiang WR, Leveque V, et al. In vitro selected Con1 subgenomic replicons resistant to 2′-C-methyl-cytidine or to R1479 show lack of cross resistance. Virology 2006; 351: 349–59.

61.Nelson D, Pockros PJ, Godofsky E, et al. High end-of-treatment response (84%) after 4 weeks of R1626, peginterferon alfa-2a (40kd) and ribavirin followed by a further 44 weeks of peginterferon alfa-2a and ribavirin. J Hepatol 2008; 48: 371.

62.Pierra C, Benzaria S, Amador A, et al. Nm 283, an efficient prodrug of the potent anti-HCV agent 2′-C-methylcytidine. Nucleosides Nucleotides Nucleic Acids 2005; 24: 767–70.

63.Pockros P, Nelson D, Godofsky E, et al. High relapse rate seen at week 72 for patients treated with R1626 combination therapy. Hepatology 2008; 48: 1349–50.

64.Pockros PJ, Nelson D, Godofsky E, et al. R1626 plus peginterferon Alfa-2a provides potent suppression of hepatitis C virus RNA and significant antiviral synergy in combination with ribavirin. Hepatology 2008; 48: 385–97.

65.Roberts SK, Cooksley G, Dore GJ, et al. Robust antiviral activity of R1626, a novel nucleoside analog: a randomized, placebo-controlled study in patients with chronic hepatitis C. Hepatology 2008; 48: 398–406.

66.Koch U, Narjes F. Allosteric inhibition of the hepatitis C virus NS5B RNA dependent RNA polymerase. Infect Disord Drug Targets 2006; 6: 31–41.

67.Koch U, Narjes F. Recent progress in the development of inhibitors of the hepatitis C virus RNA-dependent RNA polymerase. Curr Top Med Chem 2007; 7: 1302–29.

68.Beaulieu PL. Non-nucleoside inhibitors of the HCV NS5B polymerase: progress in the discovery and development of novel agents for the treatment of HCV infections. Curr Opin Investig Drugs 2007; 8: 614–34.

69.Lesburg CA, Cable MB, Ferrari E, Hong Z, Mannarino AF, Weber PC. Crystal structure of the RNA-dependent RNA polymerase from hepatitis C virus reveals a fully encircled active site. Nat Struct Biol 1999; 6: 937–43.

70.Lawitz E, Nguyen T, Younes Z. Clearance of HCV RNA with valopicitabine plus peginterferon treatment-naive patients with HCV-1 infection: Results at 24 and 48 weeks. J Hepatol 2007; 46: 9.

71.Erhardt A, Deterding K, Benhamou Y, et al. Safety, pharmacokinetics and antiviral effect of BILB 1941, a novel hepatitis C virus RNA polymerase inhibitor, after 5 days oral treatment. Antivir Ther 2009; 14: 23–32.

72.Shi ST, Herlihy KJ, Graham JP, et al. Preclinical characterization of PF-00868554, a potent nonnucleoside inhibitor of the hepatitis C virus RNA-dependent RNA polymerase. Antimicrob Agents Chemother 2009; 53: 2544–52.

73.Cooper C, Lawitz E, Ghali P, et al. Evaluation of VCH-759 monotherapy in hepatitis C infection. J Hepatol 2009; 51: 39– 46.

74.Thompson PA, Patel R, Showalter RE, Li C, Appleman JR, Steffy K. In vitro studies demonostrate that combinations of antiviral agents that include HCV polymerase inhibitor ANA598 have the potential to overcome viral resistance. Hepatology 2008; 48(Suppl): 1164.

75.Kneteman NM, Howe AY, Gao T, et al. HCV796: A selective nonstructural protein 5B polymerase inhibitor with potent anti-hepatitis C virus activity in vitro, in mice with chimeric human livers, and in humans infected with hepatitis C virus. Hepatology 2009; 49: 745–52.

76.Villano SA, Raible D, Harper D, et al. Antiviral activity of the non-nucleoside polymerase inhibitor, HCV-796, in combination with pegylated interferon alfa-2b in treatment-naive patients with chronic HCV. J Hepatol 2007; 46: 24.

77.Nettles R, Chien C, Chung E, et al. BMS-790052 is a first-in-class potent hepatitis C virus NS5A inhibitor for patients with chronic HCV infection: results from a proof-of-concept study. Hepatology 2008; 48(Suppl): 1025.

78.Einav S, Gerber D, Bryson PD, et al. Discovery of a hepatitis C target and its pharmacological inhibitors by microfluidic affinity analysis. Nat Biotechnol 2008; 26: 1019–27.

79.Gane EJ, Roberts SK, Stedman C, et al. First-in-man demonstration of potent antiviral activity with a nucleoside polymerase (R7128) and protease (R7227/ITMN-191) inhibitor combination in HCV: safety, pharmacokinetics, and virologic results from INFORM-1. J Hepatol 2009; 50(Suppl.1): 380.

80.Ge D, Fellay J, Thompson AJ, et al. Genetic variation in IL28B predicts hepatitis C treatment-induced viral clearance. Nature 2009; 461: 399–401.

81.Rauch A, Kutalik Z, Descombes P, et al. Genetic variation in IL28B is associated with chronic hepatitis C and treatment failure - A Genome-Wide Association Study. Gastroenterology 2010; 138: 1338– 45.

82.Thomas DL, Thio CL, Martin MP, et al. Genetic variation in IL28B and spontaneous clearance of hepatitis C virus. Nature 2009; 461: 798–801.

83.Barth H, Liang TJ, Baumert TF. Hepatitis C virus entry: molecular biology and clinical implications. Hepatology 2006; 44: 527–35.

84.Bartosch B, Vitelli A, Granier C, et al. Cell entry of hepatitis C virus requires a set of co-receptors that include the CD81 tetraspanin and the SR-B1 scavenger receptor. J Biol Chem 2003; 278: 41624–30.

85.Lozach PY, Amara A, Bartosch B, et al. C-type lectins L-SIGN and DC-SIGN capture and transmit infectious hepatitis C virus pseudotype particles. J Biol Chem 2004; 279: 32035–45.

86.Pileri P, Uematsu Y, Campagnoli S, et al. Binding of hepatitis C virus to CD81. Science 1998; 282: 938–41.

87.Clarke D, Griffin S, Beales L, et al. Evidence for the formation of a heptameric ion channel complex by the hepatitis C virus p7 protein in vitro. J Biol Chem 2006; 281: 37057–68.

88.Steinmann E, Whitfield T, Kallis S, et al. Antiviral effects of amantadine and iminosugar derivatives against hepatitis C virus. Hepatology 2007; 46: 330–8.

89.Steinmann E, Penin F, Kallis S, Patel AH, Bartenschlager R, Pietschmann T. Hepatitis C virus p7 protein is crucial for assembly and release of infectious virions. PLoS Pathog 2007; 3: e103.

90.Lorenz IC, Marcotrigiano J, Dentzer TG, Rice CM. Structure of the catalytic domain of the hepatitis C virus NS2-3 protease. Nature 2006; 442: 831–5.

91.Meylan E, Curran J, Hofmann K, et al. Cardif is an adaptor protein in the RIG-I antiviral pathway and is targeted by hepatitis C virus. Nature 2005; 437: 1167– 72.

92.Tellinghuisen TL, Marcotrigiano J, Rice CM. Structure of the zinc-binding domain of an essential component of the hepatitis C virus replicase. Nature 2005; 435: 374–9
 
Source
From American Journal of Transplantation

L. M. Kucirka; A. L. Singer; R. L. Ros; R. A. Montgomery; N. N. Dagher; D. L. Segev

Posted: 08/26/2010; American Journal of Transplantation © 2010 Blackwell Publishing

Abstract and Introduction

Abstract

Hepatitis C-positive (HCV(+)) candidates likely derive survival benefit from transplantation with HCV(+) kidneys, yet evidence remains inconclusive. We hypothesized that lack of good survival benefit data has led to wide practice variation. Our goal was to characterize national utilization of HCV(+) kidneys for HCV(+) recipients, and to quantify the risks/benefits of this practice. Of 93,825 deceased donors between 1995 and 2009, HCV(+) kidneys were 2.60-times more likely to be discarded (p < 0.001). However, of 6830 HCV(+) recipients, only 29% received HCV(+) kidneys. Patients over 60 relative rate (RR 0.86), women (RR 0.73) and highly sensitized patients (RR 0.42) were less likely to receive HCV(+) kidneys, while African Americans (RR 1.56), diabetics (RR 1.29) and those at centers with long waiting times (RR 1.19) were more likely to receive them. HCV(+) recipients of HCV(+) kidneys waited 310 days less than the average waiting time at their center, and 395 days less than their counterparts at the same center who waited for HCV(−) kidneys, likely offsetting the slightly higher patient (HR 1.29) and graft loss (HR 1.18) associated with HCV(+) kidneys. A better understanding of the risks and benefits of transplanting HCV(+) recipients with HCV(+) kidneys will hopefully improve utilization of these kidneys in an evidence-based manner.

Introduction

The prevalence of Hepatitis C virus (HCV) is approximately 12% among end-stage renal disease (ESRD) patients,[1] and HCV(+) patients have an increased risk of death on dialysis when compared with patients who are HCV(−).[1–4] Similarly, the prevalence of HCV is 4.2% among deceased donors.[5–7] Kidney transplantation (KT) in HCV(+) recipients is associated with slightly worse outcomes than transplantation in HCV(−) recipients, including increased risk of death and graft loss, and increased incidence of posttransplant diabetes.[8–13] However, this practice is considered a safe alternative to dialysis treatment, and several single-center studies have shown that HCV(+) recipients derive a survival benefit from KT when compared with remaining on dialysis.[14–16]

The use of HCV(+) kidneys is controversial, and initial studies recommended excluding them from the organ supply given the near certainty of HCV transmission to the recipient.[17,18] However, in 1994 a cost-benefit analysis suggested that a policy where HCV(+) kidneys were transplanted into HCV(+) recipients might provide better patient outcomes than a discard policy.[19]

Evidence suggests that outcomes of HCV(+) recipients who receive kidneys from HCV(+) donors are slightly worse than outcomes of HCV(+) recipients who receive kidneys from similar HCV(−) donors.[5,20] So if an HCV(+) kidney and a comparable HCV(−) kidney were both available for a given HCV(+) patient, the choice would be intuitive. However, a given patient never faces this decision; rather, the true clinical decision is whether to accept the HCV(+) organ offer currently at hand or to wait on dialysis for the next HCV(−) offer.[21] Whether HCV(+) candidates derive a survival benefit from being transplanted with HCV(+) kidneys (versus waiting for HCV(−) kidneys) has been a difficult question to study because no national registry collects HCV status of all candidates on the waiting list; UNOS collects HCV status only when a patient receives a kidney, not when the patient is added to the waiting list.[22] The obvious potential benefit for an HCV(+) patient to accept the currently available HCV(+) kidney, as opposed to waiting for the next available HCV(−) kidney, would be decreased waiting time and as such decreased dialysis mortality. At least one single-center study has observed this, with shorter waiting times for HCV(+) patients who accept HCV(+) kidneys.[23]

We hypothesized that the inability to quantify the survival benefit of HCV(+) KT in HCV(+) candidates has caused high discard rates of HCV(+) kidneys and varied practice patterns among those using them. We further hypothesized that those HCV(+) recipients who did receive HCV(+) kidneys would have significantly shorter waiting times (and thus lower risks of death on the waiting list) than those who waited for HCV(−) kidneys. The goals of our study were to explore national practice patterns in discard and utilization of HCV(+) kidneys for HCV(+) recipients, and to quantify risks and benefits associated with receiving an HCV(+) kidney.

Methods

Study Population

We studied 6830 HCV(+) patients who received a deceased donor KT between January 1, 1995 and February 20, 2009 as reported to UNOS. We also studied 93 825 deceased donors during the same time period where at least one organ was recovered, of whom 93 120 had information about HCV status and 3321 were HCV(+).

Recipients of HCV(+) Kidneys

To estimate the relative rate (RR) that HCV(+) recipients were transplanted with HCV(+) kidneys (as opposed to HCV(−) kidneys), we built a multivariate generalized linear model (GLM) with a Poisson family and log link as previously described,[24] adjusted for age, gender, ethnicity, insurance, body mass index (BMI), diabetes, hypertension, previous transplant, peak panel reactive antibody (PRA), years on dialysis and center waiting time, accounting for center-level clustering.

Race and Receipt of HCV(+) Kidneys

Initially, we found that African-American (AA) HCV(+) recipients had almost twice the rate of receiving an HCV(+) kidney than their non-AA HCV(+) counterparts. Since this disparity might have occurred at the center-level, such that centers with higher proportions of AA recipients utilized HCV(+) kidneys more than other centers, we adjusted for the proportion of AA recipients at each center. To further explore the relationship between race and receipt of an HCV(+) kidney, we calculated the number of AAs that would have been expected to receive HCV(+) kidneys per center if distribution had been uniformly random, by multiplying the proportion of HCV(+) recipients who were AA by the number of HCV(+) kidneys transplanted at that center. We then compared the expected and observed number of HCV(+) kidneys allocated to AA recipients for each center.

Center-level Distributions of HCV(+) Recipients and HCV(+) Donors

For each center, we calculated the total number of HCV(+) recipients and HCV(+) kidneys, and the percentage of HCV(+) recipients transplanted with HCV(+) kidneys. To better understand center clustering (i.e. what proportion of the national volume was performed by what number of centers), we compared the center-level cumulative distribution of HCV(+) recipients and HCV(+) kidneys. The more area under each cumulative distribution curve, the fewer centers that performed the bigger bulk of transplants in HCV(+) recipients. To test whether center-level variation correlated with center-level patient characteristics, we examined the distribution of the difference between the percentage of HCV (+) recipients expected to receive HCV (+) kidneys and that observed for each center. To determine the percent expected for each center, we used the GLM described above to calculate each patient's predicted probability of receiving an HCV(+) kidney based on national practice.

Waiting Time and HCV(+) Kidneys

For each center, we calculated the average waiting time among HCV(+) recipients at that center (regardless of donor HCV status). We then calculated the difference between an individual recipient's waiting time and the average waiting time at that recipient's center and compared the difference in waiting time by donor HCV status.

Discard of HCV(+) Kidneys

From donors in our study population, each kidney available for possible transplantation was analyzed separately. We built a GLM as above[24] to estimate the RR of discard of HCV(+) kidneys, adjusted for donor race, gender, age, year of recovery, cause of death, donation after cardiac death (DCD) status, creatinine, blood type, BMI, hypertension, expanded criteria donor (ECD) status and hepatitis B status (core antibody and surface antigen). Fifteen HIV(+)donors were excluded from analysis. We repeated the analysis with only non-DCD donors ages 15–45 with creatinine <2. We also repeated the analysis to examine the role of classification as 'high infectious risk' by the Center for disease control (CDC); since this was only captured after January 1, 2004, our repeated analysis was limited to donors after that date.

Survival in HCV(+) Recipients

We built a Cox proportional hazards model to examine associations between donor HCV status and (1) patient survival and (2) death-censored graft survival among HCV(+) recipients. These associations were studied within the entire cohort, and then repeated in subgroups to explore possible effect modification by race, gender, age, diabetes, PRA and BMI. All models were adjusted for donor age, ECD status, DCD status, cold ischemic time (CIT) and creatinine, and recipient race, gender, BMI, insurance, diabetes, hypertension, angina, previous malignancy, peak PRA and years on dialysis.

Results
 
Recipients of HCV(+) Kidneys

Of 6830 HCV(+) recipients, the majority (71%) received an HCV(−) kidney, with only 1998 receiving an HCV(+) kidney. This did not vary significantly by year (Figure 1A). A higher proportion of recipients of HCV(+) kidneys were AA (66.4% vs. 46.0%), diabetic (35.3% vs. 26.7%) and privately insured (24.6% vs. 20.0%), while a lower proportion were female (20.1% vs. 31.0%), Caucasian (22.2% vs. 37.8%), highly sensitized (3.6% vs. 13.8%) and retransplants (13.1% vs. 22.6%). HCV(+) donors were significantly less likely to be ECD, DCD or have a creatinine >1.5 compared to HCV(−) donors (Table 1).


Figure 1.
Temporal trends in (A) percentage of HCV(+) recipients transplanted using HCV(+) kidneys, and (B) percentage of HCV(+) kidneys discarded.

In multivariate analysis of HCV(+) recipients, we found that patients over 60 received HCV(+) kidneys 14% less often than patients under 60 (RR = 0.86, 95% CI: 0.77–0.96, p = 0.005, Table 2), and women received them 27% less often than men (RR = 0.73, 95% CI: 0.66–0.80, p < 0.001). Patients with PRA >80 were 58% less likely to receive HCV(+) kidneys compared to patients with lower PRA (RR = 0.42, 95% CI: 0.32–0.56, p < 0.001), likely due to the fact that highly sensitized patients receive higher allocation priority. Diabetes was the only comorbid condition associated with increased receipt of HCV(+) kidneys (RR = 1.29, 95% CI: 1.18–1.40, p < 0.001), consistent with the well established significantly higher dialysis death rates for diabetic patients and the resulting urgency to transplant these patients. Along those lines, patients from centers with longer waiting times were significantly more likely to receive HCV(+) kidneys (RR = 1.19 per quartile of waiting time, p = 0.002).


Race and Receipt of HCV(+) Kidneys

In a preliminary patient-level multivariate model, we found that AA HCV(+) recipients had 1.81-times the rate of receipt of HCV(+) kidneys (data not shown) compared with non-AAs. When we added to the model two center-level variables, (1) proportion of AAs at the center and (2) average waiting time at the center, we found the rate of receipt of HCV(+) kidneys in AAs was somewhat attenuated but by no means entirely explained (RR = 1.56, 95% CI: 1.39.1.75, p < 0.001). We also confirmed that, for the majority of centers (71%), the observed number of AA recipients of HCV(+) kidneys was greater than the expected number based on racial distributions at the center where they were transplanted (p < 0.001, Figure 2).

 
Figure 2.
Distribution of difference between observed and expected number of HCV(+) African-American recipients of HCV(+) kidneys at a center.

Center-level Distributions of HCV(+) Recipients and HCV(+) Donors
 
There was substantial variation between centers in the proportion of HCV(+) recipients who received HCV(+) kidneys (Figure 3A). For example, 81 centers (representing 35% of centers who transplanted HCV(+) recipients) did not use any HCV(+) kidneys for their HCV(+) patients, while 31 (13%) transplanted over half of their HCV(+) recipients with HCV(+) kidneys. The average waiting time among centers that used no HCV(+) kidneys was 567 days (range: 44–1074 days), while the average waiting time was 767 days among centers that used any of these kidneys (range: 216–1609 days). Transplantation of HCV(+) kidneys was much more clustered at a small subset of centers than transplantation of HCV(+) recipients (Figure 3B), implying wider dissemination of comfort with HCV(+) recipients than comfort with HCV(+) kidneys. Center-level variation in utilization of HCV(+) kidneys did not appear to be explained by differences in composition of centers' patients; when we calculated the percent of HCV(+) recipients expected to receive HCV (+) kidneys, based on the characteristics of these patients and national practice patterns in patients with similar characteristics, we found wide variation in expected versus observed percentages, ranging from 56% less than expected to 69% more than expected (Figure 3C).


Figure 3.
Center-level (A) distribution of the percentage of HCV(+) recipients transplanted with HCV(+) donors, (B) cumulative distribution of HCV(+) recipients and HCV(+) donors and (C) difference between observed and expected number of HCV(+) kidneys transplanted, by center.

Discard Rate of HCV(+) Kidneys
 
The proportion HCV(+) recipients who received HCV(+) kidneys increased from 20.1% in 1995 to 38.3% in 2008. However, there was little temporal variation in the proportion of HCV(+) kidneys discarded during the study period (Figure 1A). In general, HCV(+) kidneys were discarded at 2.90-times the rate of HCV(−) kidneys, even after adjusting for other factors associated with discard (95% CI: 2.52–2.68, p < 0.001) (Table 3). When we limited the analysis to kidneys recovered during 2004 and adjusted for CDC high-risk donor status, we found a similar association between HCV and discard (RR = 2.57, 95% CI: 2.47–2.68, p < 0.001, data not shown). During the study period, 53.6% of HCV(+) kidneys were discarded (a total of 3562) compared with only 22.4% of HCV(−) kidneys discarded. When the analysis was restricted to kidneys from non-DCD donors ages 15–45 with creatinine levels <2, HCV(+) kidneys were discarded at 4.72-times the rate of HCV(−) kidneys, adjusting for donor age, BMI, blood type and hypertension (95% CI: 4.44–5.03, p < 0.001). In this restricted donor pool, still 38.5% of HCV(+) kidneys were discarded (a total of 1127) compared with only 6.1% of HCV(−) kidneys discarded.

Waiting Time among Recipients with HCV

On average, HCV(+) patients who received HCV(−) kidneys waited 856 days, while those who received HCV(+) kidneys waited 469 days. Looking at this from a center-level, making comparisons among recipients within the same centers, we found that HCV(+) recipients of HCV(−) kidneys waited 85 days longer than the average waiting time at their centers, while HCV(+) recipients of HCV(+) kidneys waited 310 days less than the average waiting time at their centers. In other words, recipients of HCV(+) kidneys waited on average 395 days less than those recipients who waited for HCV(−) kidneys at the same center.

Patient Survival

Consistent with other studies, we found that, among HCV(+) patients, receipt of an HCV(+) kidney was associated with 1.29-times the hazard of death in adjusted analyses (HR = 1.29, 95% CI: 1.15–1.45, p < 0.001) (Table 4A). However, this hazard ratio only translates to a difference of 1% in 1-year survival (94% for HCV(−) kidneys vs. 93% for HCV(+) kidneys, per unadjusted Kaplan–Meier estimates) and a difference of 2% in 3-year survival (85% vs. 83%).

Furthermore, when we repeated the analysis stratified by various factors, we found that some HCV(+) subgroups did not experience any difference in survival when transplanted with HCV(+) kidneys versus HCV(−) ones. For example, non-AAs had a significantly increased hazard of death associated with receipt of an HCV(+) kidney (HR = 1.60, 95% CI: 1.35–1.90, p < 0.001) (Table 4A, left column), while this increase was not seen in African Americans (HR = 1.08, p = 0.4) (Table 4A, right column). Similarly, patients over 60, diabetics, and those with PRA >80, did not have a statistically significantly increased hazard of death associated with receipt of an HCV(+) kidney, while patients under 60 had 1.28-times the hazard of death when transplanted with HCV(+) kidneys, diabetics had 1.38-times the hazard, and those with PRA <80 had 1.32-times the hazard (p < 0.001 for all estimates).

Graft Survival

Overall, HCV(+) patients who received HCV(+) kidneys had 1.18-times the hazard of graft loss compared to those who received HCV(−) kidneys (95% CI: 1.04–1.32, p = 0.007) (Table 4B). As with patient survival, this hazard ratio translated to minimal differences in actual graft survival, with no difference at 1-year survival (91% for both HCV(−) and HCV(+) kidneys) and only 3% difference at 3 years (80% vs. 77%). In stratified models, patients under 60, patients without diabetes, patients with PRA <80, and patients with BMI <35 all had an increased hazard of graft loss associated with receipt of an HCV(+) kidney (Table 4B, left column). While the hazard of graft loss also appeared to be increased for patients over 60, diabetics, patients with PRA >80, and patients with BMI >35, these increases were not statistically significant (Table 4B, right column).

Discussion
 
Since 1995, approximately half of HCV(+) kidneys have been discarded, while 71% of HCV(+) recipients have waited on average a year longer to receive an HCV(−) kidney. The biggest center-level predictor of HCV(+) kidney utilization was waiting time; centers with longer waiting times were significantly more likely to transplant HCV(+) kidneys into HCV(+) recipients. The risk of having received an HCV(+) kidney translated to a 1% lower survival at 1 year and a 2% lower survival at 3 years, while the benefits to patients were potentially significant, as HCV(+) recipients who were transplanted with HCV(+) kidneys spent over a year less time on the waiting list than those HCV(+) recipients who waited for HCV(−) kidneys at the same transplant center.

The important clinical question is whether HCV(+) recipients derive a survival benefit from receiving an HCV(+) kidney as opposed to waiting longer for an HCV(−) kidney. Unfortunately, this clinical question has never been successfully answered, let alone in a nationally representative cohort. While several single-center studies have demonstrated that HCV(+) patients derive a survival benefit from receiving a kidney transplant (from any donor) as opposed to remaining on dialysis, no study has successfully examined whether this effect is modified by the HCV status of the donor kidney.[14–16] Unfortunately, similar to previous studies on this topic,[19,22] we were unable to answer this directly because HCV status is only captured at the time of transplant, not at the time of listing. We were, however, able to quantify the 'risk' side of the risk/benefit equation directly, showing that transplantation with an HCV(+) kidney resulted in 1% lower survival at 1 year and 2% lower survival at 3 years, and the 'benefit' side indirectly, showing that waiting for an HCV(−) kidney resulted in an extra year of dialysis. Considering that the death rate for dialysis patients on the waitlist is 7.5 per 100 person-years on average,[25] and that the rate is increased by 25% among dialysis patients with HCV,[1] opting for the currently available HCV(+) kidney rather than waiting for the next available HCV(−) kidney might be justified for the right patients. And with over 1000 HCV(+) kidneys from non-DCD donors under 45 with creatinines < 2.0 discarded during our study period, it seems that lack of organ availability did not likely drive the choice for an HCV(+) patient to wait for an HCV(−) kidney.

We found wide variation in utilization of HCV(+) kidneys across centers, with 35% of centers never transplanting an HCV(+) organ into their HCV(+) recipients over the entire 13-year study period. While this was partially explained by waiting time, there were centers with the longest 10% of waiting times that indeed transplanted HCV(+) recipients but never with HCV(+) kidneys. Furthermore, the discard rate of HCV(+) kidneys was two to six times higher than for HCV(−) kidneys, and four to seven times higher when restricting the comparison to 'ideal' donors. These findings suggest that HCV(+) kidneys are underutilized nationally, and that increasing utilization might (a) provide significant benefit for HCV(+) patients by decreasing waiting times and (b) expand the organ supply for all patients by increasing overall organ utilization.

Our study corroborates previous findings that, even for recipients who are already HCV(+), receipt of an HCV(+) kidney is associated with a small increase in hazard of death and graft loss compared to receipt of an HCV(−) kidney.[5,20] However, we also found that for certain subgroups such as older patients, diabetics or those with high PRA, the increased hazard is not observed, suggesting that the donor HCV status might not be an issue at all for these patients. Previous studies have shown an increased risk of posttransplant diabetes in HCV(+) recipients,[9,11,12] which may contribute to the increased risk of death and graft loss, and might also explain why this risk appears to be attenuated for those who had diabetes prior to transplant. Nevertheless, there may be multiple reasons that HCV(+) recipients choose to wait for HCV(−) kidneys, including patient preference, previous HCV treatment with good response, concerns about genotype coinfection, and other concerns of increased harm. CDC high-risk donor behavioral factors might also play a role in clinical decision making, although in our analysis, these factors did not attenuate the independent effect of HCV status on organ discard.

We speculate on another potential factor involved in the discard of HCV(+) kidneys, that of regulatory disincentive. Indeed, current risk-adjustment models used by the SRTR and CMS to evaluate center-specific outcomes do not account for donor HCV status,[26] and the fear of potential legal and regulatory consequences of using an organ for which the risk would not be properly adjusted has been shown to influence practice patterns.[27] The underutilization of HCV(+) kidneys might be explained by provider fears of regulatory consequences from using these organs without risks properly adjusted in these models. As such, adding donor HCV status to these models might attenuate these fears and increase national utilization of these organs. We acknowledge that this reasoning is purely speculative and not examined by our study.

AA HCV(+) recipients had high rates of receipt of HCV(+) organs compared to other races. While this was partially explained by center-level variation in utilization, we found these organs were disproportionately utilized in AAs even within many centers. More studies are needed to determine whether these decisions are occurring at the level of the provider (providers are more likely to offer HCV(+) kidneys to AA recipients), or the patient (AA recipients are more likely to accept HCV(+) kidney offers). Interestingly, this practice pattern might be reasonable in the current environment, as HCV(+) AAs transplanted with HCV(+) kidneys did not have any increased risk of death compared to HCV(+) AAs transplanted with HCV(−) kidneys, while HCV(+) kidney receipt was associated with a significant increase in mortality for patients of other races. That said, the current disparity in waiting times for AAs might be playing a role in this effect modification, and correcting these disparities might change these inferences.

Our study had the following limitations. First, national data do not exist on the HCV status of candidates on the waiting list; we could only identify HCV(+) patients among those who actually received kidneys. As such, we were unable to directly study survival benefit derived from receipt of HCV(+) kidneys compared to waiting on the list, although we provide for comparison death rates on dialysis versus increases in posttransplant death rates attributable to the HCV(+) status of the transplanted kidney. Second, HCV-RNA levels are not captured in UNOS; as such all our analyses were based on antibody status only. On the donor side, it is possible that the increase in death and graft loss may be more significant in recipients of kidneys from donors who are HCV viremic. On the recipient side, a recent review recommended restricting the use of HCV(+) kidneys to recipients with active HCV viremia.[28] Further studies are needed to better understand the relationship between HCV viremia and outcomes. Combined pegylated-interferon alpha/ribavirin therapy has shown some promise in achieving sustained virologic response in some HCV(+) ESRD patients[29] but tolerance to these regimens has been limited in some studies.[30] Third, we also did not have data on HCV genotype, so we were unable to examine whether genotype mismatch between donor and recipient contributed to the increased hazards of death in patients transplanted with HCV(+) kidneys. A study by the New England Organ Bank showed no increased risk of death or graft loss associated with HCV genotype mismatch in transplant,[31] but this has not been replicated using national data.

Our study suggests that HCV(+) kidneys are underutilized, and that tremendous variation exists in national practice patterns independent of measurable center-level characteristics. In this article, we have quantified the risks associated with transplanting HCV(+) kidneys into various subgroups of HCV(+) patients, so that these risks can be incorporated into the risk/benefit decisions made when an organ offer is considered for a given patient. We also encourage consideration of the increased risk associated with HCV(+) kidneys for risk-prediction models used to determine center-specific outcomes, as the lack of adjustment for donor HCV status might create a disincentive to the use of these organs and might contribute to the high discard rates.

References

1.Kalantar-Zadeh K, Kilpatrick RD, McAllister CJ et al. Hepatitis C virus and death risk in hemodialysis patients. J Am Soc Nephrol 2007; 18: 1584–1593.

2.Berenguer M. Treatment of chronic hepatitis C in hemodialysis patients. Hepatology 2008; 48: 1690–1699.

3.Butt AA, Skanderson M, McGinnis KA et al. Impact of hepatitis C virus infection and other comorbidities on survival in patients on dialysis. J Viral Hepat 2007; 14: 688–696.

4.Wang SM, Liu JH, Chou CY, Huang CC, Shih CM, Chen W. Mortality in hepatitis C-positive patients treated with peritoneal dialysis. Perit Dial Int 2008; 28: 183–187.

5.Bucci JR, Matsumoto CS, Swanson SJ et al. Donor hepatitis C seropositivity: Clinical correlates and effect on early graft and patient survival in adult cadaveric kidney transplantation. J Am Soc Nephrol 2002; 13: 2974–2982.

6.Pereira BJ, Wright TL, Schmid CH et al. Screening and confirmatory testing of cadaver organ donors for hepatitis C virus infection: A U.S. National Collaborative Study. Kidney Int 1994; 46: 886–892.

7.Roth D, Fernandez JA, Babischkin S et al. Detection of hepatitis C virus infection among cadaver organ donors: Evidence for low transmission of disease. Ann Intern Med 1992; 117: 470–475.

8.Abbott KC, Lentine KL, Bucci JR et al. Impact of diabetes and hepatitis after kidney transplantation on patients who are affected by hepatitis C virus. J Am Soc Nephrol 2004; 15: 3166–3174.

9.Baid-Agrawal SF, Reinke P, Schindler R et al. Impaired insulin sensitivity as an underlying mechanism linking hepatitis c and posttransplant diabetes mellitus in kidney recipients. Am J Transplant 2009; 9: 2777–2784.

10.Batty DS, Jr, Swanson SJ, Kirk AD, Ko CW, Agodoa LY, Abbott KC. Hepatitis C virus seropositivity at the time of renal transplantation in the United States: Associated factors and patient survival. Am J Transplant 2001; 1: 179–184.

11.Bloom RD, Rao V, Weng F, Grossman RA, Cohen D, Mange KC. Association of hepatitis C with posttransplant diabetes in renal transplant patients on tacrolimus. J Am Soc Nephrol 2002; 13: 1374–1380.

12.Fabrizi F, Messa P, Martin P, Takkouche B. Hepatitis C virus infection and post-transplant diabetes mellitus among renal transplant patients: A meta-analysis. Int J Artif Organs 2008; 31: 675–682.

13.Pereira BJ, Wright TL, Schmid CH, Levey AS. A controlled study of hepatitis C transmission by organ transplantation. The New England Organ Bank Hepatitis C Study Group. Lancet 1995; 345: 484–487.

14.Knoll GA, Tankersley MR, Lee JY, Julian BA, Curtis JJ. The impact of renal transplantation on survival in hepatitis C-positive end-stage renal disease patients. Am J Kidney Dis 1997; 29: 608–614.

15.Sezer S, Ozdemir FN, Akcay A, Arat Z, Boyacioglu S, Haberal M. Renal transplantation offers a better survival in HCV-infected ESRD patients. Clin Transplant 2004; 18: 619–623.

16.Bloom RD, Sayer G, Fa K, Constantinescu S, Abt P, Reddy KR. Outcome of hepatitis C virus-infected kidney transplant candidates who remain on the waiting list. Am J Transplant 2005; 5: 139–144.

17.Pereira BJ, Milford EL, Kirkman RL, Levey AS. Transmission of hepatitis C virus by organ transplantation. N Engl J Med 1991; 325: 454–460.

18.Pereira BJ, Milford EL, Kirkman RL et al. Prevalence of hepatitis C virus RNA in organ donors positive for hepatitis C antibody and in the recipients of their organs. N Engl J Med 1992; 327: 910–915.

19.Kiberd BA. Should hepatitis C-infected kidneys be transplanted in the United States? Transplantation 1994; 57: 1068–1072.

20.Bucci JR, Lentine KL, Agodoa LY, Peters TG, Schnitzler MA, Abbott KC. Outcomes associated with recipient and donor hepatitis C serology status after kidney transplantation in the United States: analysis of the USRDS/UNOS database. Clin Transpl 2004: 51–61.

21.Merion RM, Ashby VB, Wolfe RA et al. Deceased-donor characteristics and the survival benefit of kidney transplantation. JAMA 2005; 294: 2726–2733.

22.Abbott KC, Lentine KL, Bucci JR, Agodoa LY, Peters TG, Schnitzler MA. The impact of transplantation with deceased donor hepatitis c-positive kidneys on survival in wait-listed long-term dialysis patients. Am J Transplant 2004; 4: 2032–2037.

23.Mandal AK, Kraus ES, Samaniego M et al. Shorter waiting times for hepatitis C virus seropositive recipients of cadaveric renal allografts from hepatitis C virus seropositive donors. Clin Transplant 2000; 14(4 Pt 2): 391–396.

24.Zou G. A modified poisson regression approach to prospective studies with binary data. Am J Epidemiol 2004; 159: 702–706.

25.USRDS. Annual Data Report http://www.usrds.org/2009/pdf/V2_07_09.PDF. In., 2009.

26.Medicare. Hospital conditions of participation: Requirements for approval and re-approval of transplant centers to perform organ transplantation. Final Rule. In: Fed Regist, 2007: 15198–15280.

27.Abecassis MM, Burke R, Klintmalm GB et al. American society of transplant surgeons transplant center outcomes requirements–a threat to innovation. Am J Transplant 2009; 9: 1279–1286.

28.Fabrizi F, Messa P, Martin P. Current status of renal transplantation from HCV-positive donors. Int J Artif Organs 2009; 32: 251–261.

29.Rendina M, Schena A, Castellaneta NM et al. The treatment of chronic hepatitis C with peginterferon alfa-2a (40 kDa) plus ribavirin in haemodialysed patients awaiting renal transplant. J Hepatol 2007; 46: 768–774.

30.Carriero D, Fabrizi F, Uriel AJ, Park J, Martin P, Dieterich DT. Treatment of dialysis patients with chronic hepatitis C using pegylated interferon and low-dose ribavirin. Int J Artif Organs 2008; 31: 295–302.

31.Natov SN, Lau JY, Ruthazer R, Schmid CH, Levey AS, Pereira BJ. Hepatitis C virus genotype does not affect patient survival among renal transplant candidates. The New England Organ Bank Hepatitis C Study Group. Kidney Int 1999; 56: 700–706.
 
Source