Establishment of intracellular tenofovir-diphosphate as the key determinant for in vitro-in vivo translation of antiviral efficacy.

In vitro evaluation of tenofovir disproxil fumarate (TDF) and tenofovir alafenamide (TAF) revealed comparable antiviral effects with respect to the tenofovir-diphosphate (TFV-DP) level in human peripheral blood mononuclear cells (PBMCs), despite the EC50 values determined based on prodrug concentrations were nearly two orders of magnitude apart. In vivo EC50 obtained from meta-analyses were in good agreement with the in vitro results, indicating intracellular TFV-DP can be employed for in vitro-in vivo translation of viral inhibition for tenofovir prodrugs. Current analysis indicated that the intracellular concentrations of TFV-DP achieving maximal antiviral effect in vitro can be directly translatable in the clinic to accomplish maximal viral load suppression attainable by tenofovir-prodrugs.

Emergence of resistance-associated variants after failed triple therapy with vaniprevir in treatment-experienced non-cirrhotic patients with hepatitis C-genotype 1 infection: a population and clonal analysis.

BACKGROUND: Vaniprevir with P/R improved SVR rates over P/R alone in treatment-experienced patients with chronic HCV-genotype 1 infection, but treatment failure presents therapeutic challenges. We identified RAVs from non-cirrhotic patients failing to achieve SVR on vaniprevir-containing regimens from a dose/duration-ranging trial of triple-combination therapy. METHODS: Using population analysis, resistance sequencing was performed on all baseline samples and on samples at virologic failure in the vaniprevir arms. Longitudinal clonal analyses were performed on viral isolates from six vaniprevir recipients experiencing breakthrough viremia. RESULTS: Baseline RAVs were detected in two patients subsequently experiencing virologic failure. At virologic failure, the majority of RAVs had substitutions at R155, A156, or D168. Clonal analyses identified novel double/triple variants emerging with continuing vaniprevir dosing. CONCLUSIONS: RAVs were predominantly observed at R155, A156, and/or D168 during virologic failure on vaniprevir/P/R. Double/triple RAVs were identified in patients remaining viremic on triple therapy, suggesting evolution of resistance under selective pressure.

Discovery of MK-5172, a Macrocyclic Hepatitis C Virus NS3/4a Protease Inhibitor.

A new class of HCV NS3/4a protease inhibitors containing a P2 to P4 macrocyclic constraint was designed using a molecular modeling-derived strategy. Building on the profile of previous clinical compounds and exploring the P2 and linker regions of the series allowed for optimization of broad genotype and mutant enzyme potency, cellular activity, and rat liver exposure following oral dosing. These studies led to the identification of clinical candidate 15 (MK-5172), which is active against genotype 1-3 NS3/4a and clinically relevant mutant enzymes and has good plasma exposure and excellent liver exposure in multiple species.