title: The Combination of Grazoprevir, a Hepatitis C Virus (HCV) NS3/4A Protease Inhibitor, and Elbasvir, an HCV NS5A Inhibitor, Demonstrates a High Genetic Barrier to Resistance in HCV Genotype 1a Replicons.
abstract: The selection of resistance-associated variants (RAVs) against single agents administered to patients chronically infected with hepatitis C virus (HCV) necessitates that direct-acting antiviral agents (DAAs) targeting multiple viral proteins be developed to overcome failure resulting from emergence of resistance. The combination of grazoprevir (formerly MK-5172), an NS3/4A protease inhibitor, and elbasvir (formerly MK-8742), an NS5A inhibitor, was therefore studied in genotype 1a (GT1a) replicon cells. Both compounds were independently highly potent in GT1a wild-type replicon cells, with 90% effective concentration (EC90) values of 0.9 nM and 0.006 nM for grazoprevir and elbasvir, respectively. No cross-resistance was observed when clinically relevant NS5A and NS3 RAVs were profiled against grazoprevir and elbasvir, respectively. Kinetic analyses of HCV RNA reduction over 14 days showed that grazoprevir and elbasvir inhibited prototypic NS5A Y93H and NS3 R155K RAVs, respectively, with kinetics comparable to those for the wild-type GT1a replicon. In combination, grazoprevir and elbasvir interacted additively in GT1a replicon cells. Colony formation assays with a 10-fold multiple of the EC90 values of the grazoprevir-elbasvir inhibitor combination suppressed emergence of resistant colonies, compared to a 100-fold multiple for the independent agents. The selected resistant colonies with the combination harbored RAVs that required two or more nucleotide changes in the codons. Mutations in the cognate gene caused greater potency losses for elbasvir than for grazoprevir. Replicons bearing RAVs identified from resistant colonies showed reduced fitness for several cell lines and may contribute to the activity of the combination. These studies demonstrate that the combination of grazoprevir and elbasvir exerts a potent effect on HCV RNA replication and presents a high genetic barrier to resistance. The combination of grazoprevir and elbasvir is currently approved for chronic HCV infection.
authors.affiliation: Department of Infectious Diseases, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA fred.lahser@merck.com.
authors.forename: Frederick C
authors.identifier: 0000-0003-4902-0435
authors.initials: FC
authors.lastname: Lahser
authors.affiliation: Department of Infectious Diseases, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA.
authors.forename: Karin
authors.initials: K
authors.lastname: Bystol
authors.affiliation: Department of Infectious Diseases, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Curry
authors.affiliation: Department of Infectious Diseases, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA.
authors.forename: Patricia
authors.initials: P
authors.lastname: McMonagle
authors.affiliation: Department of In Vitro Pharmacology, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA.
authors.forename: Ellen
authors.initials: E
authors.lastname: Xia
authors.affiliation: Department of Infectious Diseases, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Ingravallo
authors.affiliation: Department of Infectious Diseases, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Chase
authors.affiliation: Department of Infectious Diseases, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA.
authors.forename: Rong
authors.initials: R
authors.lastname: Liu
authors.affiliation: Department of Infectious Diseases, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA.
authors.forename: Todd
authors.initials: T
authors.lastname: Black
authors.affiliation: Department of Infectious Diseases, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA Vaccine Research, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA.
authors.forename: Daria
authors.initials: D
authors.lastname: Hazuda
authors.affiliation: Department of Infectious Diseases, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA.
authors.forename: Anita Y M
authors.initials: AY
authors.lastname: Howe
authors.affiliation: Department of Infectious Diseases, Merck Research Laboratories, Merck & Co., Inc., Kenilworth, New Jersey, USA.
authors.forename: Ernest
authors.initials: E
authors.lastname: Asante-Appiah
mesh_terms: D000577:Amides; D000998:Antiviral Agents / Q000494:pharmacology*; D001572:Benzofurans / Q000494:pharmacology; D002219:Carbamates; D003521:Cyclopropanes; D004359:Drug Therapy, Combination; D005838:Genotype; D016174:Hepacivirus / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D011480:Protease Inhibitors / Q000494:pharmacology*; D011810:Quinoxalines / Q000494:pharmacology*; D012093:Replicon / Q000187:drug effects / Q000235:genetics; D012254:Ribavirin / Q000494:pharmacology; D013449:Sulfonamides; D047029:Lactams, Macrocyclic
chemical_list: D000577:Amides; D000998:Antiviral Agents; D001572:Benzofurans; D002219:Carbamates; D003521:Cyclopropanes; D007093:Imidazoles; D011480:Protease Inhibitors; D011810:Quinoxalines; D012254:Ribavirin; D013449:Sulfonamides; C578009:grazoprevir; D047029:Lactams, Macrocyclic; C000589335:elbasvir