The Discovery of Ledipasvir (GS-5885), a Potent Once-Daily Oral NS5A Inhibitor for the Treatment of Hepatitis C Virus Infection

John O. Link, James G. Taylor, Lianhong Xu, Michael L Mitchell, Hongyan Guo, Hongtao Liu, Darryl Kato, Thorsten Kirschberg, Jianyu Sun, Neil Squires, Jay Parrish, Terry Kellar, Zheng-Yu Yang, Chris Yang, Mike Matles, Yujin Wang, Kelly Wang, Guofeng Cheng, Yang Tian, Erik Mogalian, Elsa Mondou, Melanie Cornpropst, Jason Perry, and Manoj C. Desai

J. Med. Chem., Just Accepted Manuscript • Publication Date (Web): 09 Dec 2013

Downloaded from http://pubs.acs.org on December 11, 2013

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The Discovery of Ledipasvir (GS-5885), a Potent Once-Daily Oral NS5A Inhibitor for the Treatment of Hepatitis C Virus Infection

John O. Link,*† James G. Taylor,† Lianhong Xu,† Michael Mitchell,† Hongyan Guo,† Hongtao Liu,† Darryl Kato,† Thorsten Kirschberg,† Jianyu Sun,† Neil Squires,† Jay Parrish,† Terry Keller,† Zheng-Yu Yang,† Chris Yang,‡ Mike Matles,‡ Yujin Wang,‡ Kelly Wang,‡ Guofeng Cheng,¥ Yang Tian,¥ Erik Mogalian,± Elsa Mondou,≠ Melanie Cornpropst, ≠ Jason Perry,÷ and Manoj C. Desai†

†Medicinal Chemistry, ‡Drug Metabolism, ¥Biology, ± Formulation and Process Development, ≠Clinical Research, ÷ Structural Chemistry, Gilead Sciences, 333 Lakeside Drive, Foster City, CA 94404

Abstract

A new class of highly potent NS5A inhibitors with an unsymmetric benzimidazole-difluorofluorene-imidazole core and distal [2.2.1]azabicyclic ring system was discovered. Optimization of antiviral potency and pharmacokinetics led to the identification of 39 (ledipasvir, GS-5885). Compound 39 (GT1a replicon EC50 = 31 pM) has an extended plasma half-life of 37-45 hours in healthy volunteers, and produces a rapid > 3 log10 viral load reduction in monotherapy at oral doses of 3 milligrams or greater with once-daily dosing in genotype 1a HCV infected patients. 39 has been shown to be safe and efficacious with SVR12 rates up to 100% when used in combination with direct-acting antivirals having complementary mechanisms.

Introduction

Hepatitis C virus (HCV) infection is a significant public health concern with approximately 170 million infected individuals worldwide, and is the leading cause of liver transplant and hepatocellular carcinoma.1 HCV is the most common chronic blood-borne pathogen in the U.S., and the Center for Disease Control and the U.S. Preventative Services Task Force are aligned in recommending that all “babyboomers” (individuals born between 1945 and 1965) undergo testing for HCV infection.2 Until recently, the standard of care for treatment of genotype 1 (GT1) infection (60% of total infections worldwide among the seven known genotypes, with both GT1a and GT1b as major subtypes)3 consisted of weekly pegylated interferon (PEG) injections and twice daily oral ribavirin (RBV) for 24 or 48 weeks (duration based on response-guided therapy). PEG/RBV treatments achieve up to 54-63% sustained virologic response (SVR) in GT1 patients,4 but treatment is accompanied by considerable toxicity including flu-like symptoms, depression, and anemia.5 Tripletherapy containing PEG/RBV combined with three times daily dosing of the recently approved direct-acting antiviral (DAA) protease inhibitor telaprevir or boceprevir has improved the GT1 HCV SVR rates to 66-79% for treatment naïve patients, but with increased toxicities including rash (telaprevir) or grade 3/4 anemia.6 Prior null responders (patients who attained less than a 1 log viral load reduction on PEG/RBV) are not indicated for retreatment with PEG/RBV due to SVR rates <10%, with minimal improvement to 29% for patients undergoing triple-therapy.7 Finally, a growing number of patients are identified as interferon intolerant or unwilling to take interferon. PEG-free therapy is necessary to serve a broader patient population, improve outcomes, and provide a safer, simpler regimen.8

We have sought to identify safe oral drugs for combination treatment of HCV infection. In addition to programs targeting the NS3 protease,9 NS5B polymerase (both nucleotides10 and non-nucleotides11), we initiated an NS5A inhibitor program with the goal of identifying an agent with characteristics that would allow its use in combination with DAAs having complementary mechanisms to achieve high SVR rates with a short treatment duration.

Despite significant study, the mechanistic role of NS5A in the HCV life-cycle remains enigmatic.12 NS5A has no known enzymatic activity, and has no homologs in prokaryotes or eukaryotes. Nonetheless, the protein is critical for HCV viability; in clinical monotherapy studies NS5A inhibitors produce the most rapid viral load declines of any HCV antiviral class. It has been postulated that this rapid decline in HCV RNA is based on inhibition of viral replication (as with NS3 and NS5B inhibitors), and additional inhibition of virion assembly or secretion from infected cells.13

Early NS5A inhibitors were found empirically through screening of the GT1b replicon. Several series of lipophilic proline, proline-mimetic, or alanine-amide inhibitors of the GT1b replicon had been discovered (1-3, Figure 1),14 but these inhibitors typically have ~1000 fold weaker activity against the GT1a replicon.15 A polyaromatic pyridopyrimidine class (4) affords nanomolar activity against both GT1a and 1b replicons.16 Dimeric series provide potent GT1b-active stilbene diamide inhibitors (5 discovered from monomer series 1),17 and highly potent GT1a and 1b active bis-imidazole biphenyl inhibitors including daclatasvir 6 (BMS-790052, GT1a EC50 = 50 pM), which achieved clinical proof-of-concept for the NS5A mechanism.18 NS5A has emerged as an important drug target for the treatment of HCV infection.19

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