Drug transporter and cytochrome P450 expression is regulated by shared nuclear receptors and, hence, an inducer should induce both, although the magnitude may differ. The objective of this study was to establish relative induction relationships between CYP3A and drug transporters (P‐glycoprotein (P‐gp), organic anion transporting polypeptide (OATP), and breast cancer resistance protein (BCRP)) or other P450s (CYP2C9 and CYP1A2) using ascending doses of the prototypical pregnane xenobiotic receptor (PXR) agonist, rifampin, to elicit weak, moderate, and strong PXR agonism. Healthy subjects received dabigatran etexilate, pravastatin, rosuvastatin, and a midazolam/tolbutamide/caffeine cocktail before and after rifampin 2, 10, 75, or 600 mg q.d. Unlike CYP3A, only moderate induction of P‐gp, OATP, and CYP2C9 was observed and dose‐dependent induction of P‐gp, OATP, and CYP2C9 was always one drug–drug interaction category lower than observed for CYP3A, even when correcting for probe drug sensitivity. Data from this study establish proof‐of‐concept that P450 induction data can be leveraged to inform on the effect on transporters.

c GS-5885 is a novel hepatitis C virus (HCV) NS5A inhibitor. In a 3-day monotherapy study in treatment-naive genotype 1a (GT1a) and GT1b HCV-infected subjects, median viral load reductions ranged from 2.3 to 3.3 log 10 HCV RNA IU/ml across dosing cohorts (1, 3, 10, 30, or 90 mg once daily). Here, we report viral sequencing and phenotypic analysis of clinical isolates from this study. Detection of baseline NS5A amino acid substitutions at positions 28, 30, 31, or 93 in GT1a was associated with a reduced treatment response. In the GT1b cohort, Y93H was detected in 100% of subjects at day 4 or 14. In the Gt1a cohort, population sequencing detected NS5A resistance-associated mutations at day 4 or 14 for 3/10 subjects at the 1-mg dose and for all subjects dosed at >3 mg. A subset of mutants that confer a low level of reduced susceptibility to GS-5885 was not detected by population sequencing at the 30-and 90-mg doses. Subject-derived M28T, Q30R, L31M, and Y93C mutations all conferred >30-fold reductions in GS-5885 and daclatasvir susceptibilities in vitro. Site-directed NS5A mutants also showed reduced susceptibility to GS-5885. However, all NS5A mutants tested remained fully susceptible to other classes of direct-acting antivirals (DAAs), interferon alpha, and ribavirin. Importantly, the nonoverlapping resistance profile and high potency of GS-5885 support its further development with other direct-acting antivirals for the treatment of chronic HCV. (This study has been registered at ClinicalTrials.gov under registration number NCT01193478.) H epatitis C virus (HCV) infection is a global health issue, with approximately 170 million people infected worldwide (1).The standard of care (SOC) has been pegylated alpha interferon and ribavirin until the more recent approval of two NS3 protease inhibitors, telaprevir and boceprevir, for use in conjunction with pegylated alpha interferon and ribavirin (1-3). The last several years have seen a great expansion of new direct-acting antivirals (DAAs) in clinical development to augment or supplant treatment with pegylated alpha interferon and ribavirin. HCV nonstructural protein 5A (NS5A) has emerged as a viable and attractive viral target for small-molecule inhibition. Although there is no known enzymatic activity for NS5A, it is essential for viral replication (4). The first NS5A replication complex inhibitor to show efficacy in the clinic was daclatasvir (BMS-790052) (5). This compound elicited rapid and profound reductions in HCV RNA and validated NS5A as a clinical target. Sequence analysis of clinical isolates following daclatasvir monotherapy identified the main resistanceassociated mutations (RAMs) at NS5A amino acid positions 28, 30, 31, and 93 (6).In addition to daclatasvir, several other NS5A replication complex inhibitors have entered the clinic, including GS-5885, PPI-461, ABT-267, and GSK2336805 (7-10). In addition, preclinical data have recently been described for several other NS5A replication complex inhibitors, including EDP-239, IDX719, MK-4882, , highlighting ...

Rifampin demonstrated dose‐dependent relative induction between cytochrome P (CYP)3A and P‐glycoprotein (P‐gp), organic anion transporting polypeptides (OATPs), or CYP2C9; P‐gp, OATP, and CYP2C9 induction was one drug–drug interaction (DDI) category lower than that observed for CYP3A across a wide range of pregnane X receptor (PXR) agonism. The objective of this study was to determine if these relationships could be utilized to predict transporter induction by other CYP3A inducers (rifabutin and carbamazepine) and of another P‐gp substrate, sofosbuvir. Healthy subjects received sofosbuvir and a six‐probe drug cassette before and after 300 mg q.d. rifabutin or 300 mg b.i.d. carbamazepine. Induction of P‐gp, CYP2C9, and decreased sofosbuvir exposure were successfully predicted by observed CYP3A induction. Carbamazepine induction of OATP was underpredicted, likely due to reported additional non‐PXR agonism. The results demonstrate that the effect of a PXR agonist on CYP3A can be leveraged to inform on induction liability for other primarily PXR‐regulated P450s/transporters, allowing for prioritization of targeted DDI assessments during new drug development.

a; Gilead Sciences, Foster City, California, USA b Velpatasvir (VEL, GS-5816) is a novel pan-genotypic hepatitis C virus (HCV) nonstructural protein 5A (NS5A) inhibitor with activity against genotype 1 (GT1) to GT6 HCV replicons. In a phase 1b 3-day monotherapy study, patients treated with a 150-mg dose of GS-5816 had a mean maximal HCV RNA decline of >3.3 log 10 IU/ml in GT1a, -1b, -2, -3, and -4. This report characterizes virologic resistance to VEL in these patients. NS5A resistance-associated substitutions (RASs) were detected by deep sequencing (1% cutoff) pretreatment in 22/70 patients, i.e., 10/35 (29%) patients with GT1a, 1/8 (13%) with GT1b, 4/8 (50.0%) with GT2, 5/17 (29.4%) with GT3, and 2/2 (100.0%) with GT4. In GT1a and GT3 patients, pretreatment RASs were associated with a slightly reduced HCV RNA response compared to that of patients without pretreatment RASs; among patients with GT1b, GT2, and GT4, no significant difference in response was observed in those with or without pretreatment RASs. Following treatment, the pattern of emergent RASs was more complex for GT1a than for the other genotypes. In GT1a, substitutions emerged at positions M28, Q30, L31, P32, H58, E92, and Y93, with the most prevalent substitutions at positions Y93, M28, and L31. RASs were observed at two positions in GT1b and GT2 (Y93 and L31), three positions in GT3 (Y93, L31, and E92), and four positions in GT4 (L28, M31, P32L, and Y93). RASs that were present pretreatment persisted through the 48-week follow-up period; however, RASs emerging during treatment were more likely to decline both in prevalence and in frequency within the viral population during follow-up. (This study has been registered at ClinicalTrials.gov under registration no. NCT01740791.) H epatitis C virus (HCV) infects an estimated 180 million people worldwide (1). Infection can lead to cirrhosis, hepatocellular carcinoma, and other complications. Novel direct-acting antiviral agents (DAAs) are being developed in combination with pegylated interferon (PegIFN)/ribavirin (RBV) and are also being pursued as components of IFN-free and IFN/RBV-free regimens to improve efficacy and shorten treatment duration. Recently, new DAAs that are well tolerated and highly effective have been approved for the treatment of chronic HCV infection. In December 2013, the FDA approved Sovaldi (sofosbuvir [SOF]; Gilead Sciences), a once-daily pan-genotypic oral nucleotide analog polymerase inhibitor (NI) for the treatment of HCV infection as a component of a combination antiviral treatment regimen for patients with genotype 1 (GT1), GT2, GT3, or GT4 infection (2, 3). The protease inhibitor (PI) Olysio (simeprevir; Janssen Pharmaceutica), in combination with PegIFN/RBV, also received FDA approval in December 2013. Simeprevir has better activity against multiple genotypes than the PIs boceprevir and telaprevir but weak activity against GT2 and no activity against GT3 (4). Another recently approved treatment of GT1 HCV infection in the United States and Europe is Harvoni (Gilead Scien...

In order to assess the natural variation in susceptibility to hepatitis C virus (HCV) NS3 protease inhibitors (PIs) among untreated HCV patient samples, the susceptibilities of 39 baseline clinical isolates were determined using a transient-replication assay on a panel of HCV PIs, including two ␣-ketoamides (VX-950 and SCH-503034) and three macrocyclic inhibitors (MK-7009, ITMN-191, and TMC-435350). Some natural variation in susceptibility to all HCV PIs tested was observed among the baseline clinical isolates. The susceptibility to VX-950 correlated strongly with the susceptibility to SCH-503034. A moderate correlation was observed between the susceptibilities to ITMN-191 and MK-7009. In contrast, the phenotypic correlations between the ␣-ketoamides and macrocyclic inhibitors were significantly lower. This difference is partly attributable to reduced susceptibility of the HCV variants containing the NS3 polymorphism Q80K (existing in 47% of genotype 1a isolates) to the macrocyclic compounds but no change in the sensitivity of the same variants to the ␣-ketoamides tested. Our results suggest that the natural variation in baseline susceptibility may contribute to different degrees of antiviral response among patients in vivo, particularly at lower doses.Hepatitis C virus (HCV) is characterized by a high degree of genetic diversity because of its rapid replication rate and turnover, combined with the poor fidelity of the HCV RNA-dependent RNA polymerase (RdRp) (3, 5, 32). The nucleotide sequences among the six different genotypes (GTs) differ at 30 to 35% of nucleotide sites (25,26). Each of the six major GTs of HCV contains a series of closely related subtypes whose nucleotide sequences typically differ from each other by 20 to 25%. Furthermore, 5 to 8% sequence divergence is present between individual strains (variants) of HCV within a given subtype. A comprehensive analysis of HCV NS3 sequences from a larger number of GT-1 isolates found that amino acid polymorphisms were detected all along the protease sequence, including residues associated either with resistance to HCV protease inhibitors (PIs) (V36, I170, and D168) or with compensatory mutations (I72, T72, Q86, and I153) (1, 2, 30). However, many questions remain, including whether natural variation in the NS3 protease sequence impacts the susceptibility of HCV to PIs currently in development and whether there are any relationships among the chemotypes of the PIs and their baseline susceptibilities.Hepatitis C virus NS3/4A serine PIs have demonstrated potent antiviral activity in subjects infected with HCV GT-1 by specifically blocking NS3/4A protease-dependent HCV polyproprotein processing. Among these PIs, VX-950 (telaprevir) and SCH-503034 (boceprevir), the two most clinically advanced NS3/4A serine PIs, are both ␣-ketoamide compounds that covalently bind to the active-site serine of the protease (6,9,10,14,16,22). These drugs also have similar resistance profiles. Mutations V36A/M, T54A, R155K, and A156S in the NS3 protease gene, conferring a low level ...