Discovery of macrocyclic HDACs 1, 2, and 3 selective inhibitors for HIV latency reactivation.

A series of unique macrocyclic HDACs 1, 2, and 3 selective inhibitors were identified with good enzymatic activity and high selectivity over HDACs 6 and 8. These macrocyclic HDAC inhibitors used an ethyl ketone as the zinc-binding group. Compounds 25 and 26 stood out as leads due to their low double-digit nM EC50s in the 2C4 cell-based HIV latency reactivation assay. The PK profiles of these macrocyclic HDAC inhibitors still needed improvement.

Redefining the Histone Deacetylase Inhibitor Pharmacophore: High Potency with No Zinc Cofactor Interaction.

A novel series of histone deacetylase (HDAC) inhibitors lacking a zinc-binding moiety has been developed and described herein. HDAC isozyme profiling and kinetic studies indicate that these inhibitors display a selectivity preference for HDACs 1, 2, 3, 10, and 11 via a rapid equilibrium mechanism, and crystal structures with HDAC2 confirm that these inhibitors do not interact with the catalytic zinc. The compounds are nonmutagenic and devoid of electrophilic and mutagenic structural elements and exhibit off-target profiles that are promising for further optimization. The efficacy of this new class in biochemical and cell-based assays is comparable to the marketed HDAC inhibitors belinostat and vorinostat. These results demonstrate that the long-standing pharmacophore model of HDAC inhibitors requiring a metal binding motif should be revised and offers a distinct class of HDAC inhibitors.

Discovery of Ethyl Ketone-Based Highly Selective HDACs 1, 2, 3 Inhibitors for HIV Latency Reactivation with Minimum Cellular Potency Serum Shift and Reduced hERG Activity.

We describe the discovery of histone deacetylase (HDACs) 1, 2, and 3 inhibitors with ethyl ketone as the zinc-binding group. These HDACs 1, 2, and 3 inhibitors have good enzymatic and cellular activity. Their serum shift in cellular potency has been minimized, and selectivity against hERG has been improved. They are also highly selective over HDACs 6 and 8. These inhibitors contain a variety of substituted heterocycles on the imidazole or oxazole scaffold. Compounds 31 and 48 stand out due to their good potency, high selectivity over HDACs 6 and 8, reduced hERG activity, optimized serum shift in cellular potency, and good rat and dog PK profiles.

Discovery of an Anion-Dependent Farnesyltransferase Inhibitor from a Phenotypic Screen.

By employing a phenotypic screen, a set of compounds, exemplified by 1, were identified which potentiate the ability of histone deacetylase inhibitor vorinostat to reverse HIV latency. Proteome enrichment followed by quantitative mass spectrometric analysis employing a modified analogue of 1 as affinity bait identified farnesyl transferase (FTase) as the primary interacting protein in cell lysates. This ligand-FTase binding interaction was confirmed via X-ray crystallography and temperature dependent fluorescence studies, despite 1 lacking structural and binding similarity to known FTase inhibitors. Although multiple lines of evidence established the binding interaction, these ligands exhibited minimal inhibitory activity in a cell-free biochemical FTase inhibition assay. Subsequent modification of the biochemical assay by increasing anion concentration demonstrated FTase inhibitory activity in this novel class. We propose 1 binds together with the anion in the active site to inhibit farnesyl transferase. Implications for phenotypic screening deconvolution and HIV reactivation are discussed.

Discovery of Highly Selective and Potent HDAC3 Inhibitors Based on a 2-Substituted Benzamide Zinc Binding Group.

The selectivity of histone deacetylase inhibitors (HDACis) is greatly impacted by the zinc binding groups. In an effort to search for novel zinc binding groups, we applied a parallel medicinal chemistry (PMC) strategy to quickly synthesize substituted benzamide libraries. We discovered a series containing 2-substituted benzamides as the zinc binding group which afforded highly selective and potent HDAC3 inhibitors, exemplified by compound 16 with a 2-methylthiobenzamide. Compound 16 inhibited HDAC3 with an IC50 of 30 nM and with unprecedented selectivity of >300-fold over all other HDAC isoforms. Interestingly, a subtle change of the 2-methylthio to a 2-hydroxy benzamide in 20 retains HDAC3 potency but loses all selectivity over HDAC 1 and 2. This significant difference in selectivity was rationalized by X-ray crystal structures of HDACis 16 and 20 bound to HDAC2, revealing different binding modes to the catalytic zinc ion. This series of HDAC3 selective inhibitors served as tool compounds for investigating the minimal set of HDAC isoforms that must be inhibited for the HIV latency activation in a Jurkat 2C4 cell model and potentially as leads for selective HDAC3 inhibitors for other indications.

Development of a selective HDAC inhibitor aimed at reactivating the HIV latent reservoir.

The synthesis and SAR development of a trisubstituted imidazole HDAC inhibitor is described. The compounds were synthesized with high diastereocontrol by leveraging Ellman sulfinyl imine chemistry. Structural elucidation provided insight into binding mode and supported design rational. Pharmacokinetic properties of lead compounds were determined.

Selective Class I HDAC Inhibitors Based on Aryl Ketone Zinc Binding Induce HIV-1 Protein for Clearance.

HIV persistence in latently infected, resting CD4+ T cells is broadly considered a barrier to eradicate HIV. Activation of the provirus using latency-reversing agents (LRAs) followed by immune-mediated clearance to purge reservoirs has been touted as a promising therapeutic approach. Histone deacetylases (HDACs) and histone acetyltransferases (HATs) control the acetylation level of lysine residues in histones to regulate the gene transcription. Several clinical HDAC inhibitors had been examined as LRAs, which induced HIV activation in vitro and in vivo. Here we report the discovery of a series of selective and potent class I HDAC inhibitors based on aryl ketones as a zinc binding group, which reversed HIV latency using a Jurkat model of HIV latency in 2C4 cells. The SAR led to the discovery of a highly selective class I HDAC inhibitor 10 with excellent potency. HDACi 10 induces the HIV gag P24 protein in patient latent CD4+ T cells.

Cellular Gene Modulation of HIV-Infected CD4 T Cells in Response to Serial Treatment with the Histone Deacetylase Inhibitor Vorinostat.

Histone deacetylase inhibitors (HDACi) are the most widely studied HIV latency-reversing agents (LRAs). The HDACi suberoylanilide hydroxamic acid (vorinostat [VOR]) has been employed in several clinical HIV latency reversal studies, as well as in vitro models of HIV latency, and has been shown to effectively induce HIV RNA and protein expression. Despite these findings, response to HDACi can vary, particularly with intermittent dosing, and information is lacking on the relationship between the host transcriptional response and HIV latency reversal. Here, we report on global gene expression responses to VOR and examine the longevity of the transcriptional response in various cellular models. We found that many genes are modulated at 6 h post-VOR treatment in HCT116, Jurkat, and primary resting CD4 T cells, yet return to baseline levels after an 18-h VOR-free period. With repeat exposure to VOR in resting CD4 T cells, we found similar and consistent transcriptional changes at 6 h following each serial treatment. In addition, serial exposure in HIV-infected suppressed donor CD4 T cells showed consistent transcriptional changes after each exposure to VOR. We identified five host genes that were strongly and consistently modulated following histone deacetylase (HDAC) inhibition; three (H1F0, IRGM, and WIPI49) were upregulated, and two (PHF15 and PRDM10) were downregulated. These genes demonstrated consistent modulation in peripheral blood mononuclear cell (PBMC) samples from HIV-positive (HIV+) participants who received either single or multiple doses of 400 mg of VOR. Interestingly, the host transcriptional response did not predict induction of cell-associated HIV RNA, suggesting that other cellular factors play key roles in HIV latency reversal in vivo despite robust HDACi pharmacological activity.IMPORTANCE Histone deacetylase inhibitors are widely studied HIV latency-reversing agents (LRAs). VOR, an HDACi, induces histone acetylation and chromatin remodeling and modulates host and HIV gene expression. However, the relationship between these events is poorly defined, and clinical studies suggest diminished HIV reactivation in resting CD4 T cells with daily exposure to VOR. Our study provides evidence that VOR induces a consistent level of host cell gene transcription following intermittent exposure. In addition, in response to VOR exposure a gene signature that was conserved across single and serial exposures both in vitro and in vivo was identified, indicating that VOR can consistently and reproducibly modulate transcriptional host responses. However, as the HIV response to HDACi declines over time, other factors modulate viral reactivation in vivo despite robust HDAC activity. The identified host gene VOR biomarkers can be used for monitoring the pharmacodynamic activity of HDAC inhibitors.

Discovery of ethyl ketone-based HDACs 1, 2, and 3 selective inhibitors for HIV latency reactivation.

A novel series of ethyl ketone based HDACs 1, 2, and 3 selective inhibitors have been identified with good enzymatic and cellular activity and high selectivity over HDACs 6 and 8. These inhibitors contain a spirobicyclic group in the amide region. Compound 13 stands out as a lead due to its good potency, high selectivity, and reasonable rat and dog PK. Compounds 33 and 34 show good potency and rat PK profiles as well.

Superinfection and cure of infected cells as mechanisms for hepatitis C virus adaptation and persistence.

RNA viruses exist as a genetically diverse quasispecies with extraordinary ability to adapt to abrupt changes in the host environment. However, the molecular mechanisms that contribute to their rapid adaptation and persistence in vivo are not well studied. Here, we probe hepatitis C virus (HCV) persistence by analyzing clinical samples taken from subjects who were treated with a second-generation HCV protease inhibitor. Frequent longitudinal viral load determinations and large-scale single-genome sequence analyses revealed rapid antiviral resistance development, and surprisingly, dynamic turnover of dominant drug-resistant mutant populations long after treatment cessation. We fitted mathematical models to both the viral load and the viral sequencing data, and the results provided strong support for the critical roles that superinfection and cure of infected cells play in facilitating the rapid turnover and persistence of viral populations. More broadly, our results highlight the importance of considering viral dynamics and competition at the intracellular level in understanding rapid viral adaptation. Thus, we propose a theoretical framework integrating viral and molecular mechanisms to explain rapid viral evolution, resistance, and persistence despite antiviral treatment and host immune responses.

Identification of proximal biomarkers of PKC agonism and evaluation of their role in HIV reactivation.

DESIGN: The HIV latent CD4+ T cell reservoir is broadly recognized as a barrier to HIV cure. Induction of HIV expression using protein kinase C (PKC) agonists is one approach under investigation for reactivation of latently infected CD4+ T cells (Beans et al., 2013; Abreu et al., 2014; Jiang et al., 2014; Jiang and Dandekar, 2015). We proposed that an increased understanding of the molecular mechanisms of action of PKC agonists was necessary to inform on biological signaling and pharmacodynamic biomarkers. RNA sequencing (RNA Seq) was applied to identify genes and pathways modulated by PKC agonists. METHODS: Human CD4+ T cells were treated ex vivo with Phorbol 12-myristate 13-acetate, prostatin or ingenol-3-angelate. At 3 h and 24 h post-treatment, cells were harvested and RNA-Seq was performed on RNA isolated from cell lysates. The genes differentially expressed across the PKC agonists were validated by quantitative RT-PCR (qPCR). A subset of genes was evaluated for their role in HIV reactivation using siRNA and CRISPR approaches in the Jurkat latency cell model. RESULTS: Treatment of primary human CD4+ T cells with PKC agonists resulted in alterations in gene expression. qPCR of RNA Seq data confirmed upregulation of 24 genes, including CD69, Egr1, Egr2, Egr3, CSF2, DUSP5, and NR4A1. Gene knockdown of Egr1 and Egr3 resulted in reduced expression and decreased HIV reactivation in response to PKC agonist treatment, indicating a potential role for Egr family members in latency reversal. CONCLUSION: Overall, our results offer new insights into the mechanism of action of PKC agonists, biomarkers of pathway engagement, and the potential role of EGR family in HIV reactivation.

A Novel Assay to Measure the Magnitude of the Inducible Viral Reservoir in HIV-infected Individuals.

BACKGROUND: Quantifying latently infected cells is critical to evaluate the efficacy of therapeutic strategies aimed at reducing the size of the long-lived viral reservoir, but the low frequency of these cells makes this very challenging. METHODS: We developed TILDA (Tat/rev Induced Limiting Dilution Assay) to measure the frequency of cells with inducible multiply-spliced HIV RNA, as these transcripts are usually absent in latently infected cells but induced upon viral reactivation. TILDA requires less than a million cells, does not require RNA extraction and can be completed in two days. FINDINGS: In suppressed individuals on ART, we found the median frequency of latently infected CD4 + T cells as estimated by TILDA to be 24 cells/million, which was 48 times more than the frequency measured by the quantitative viral outgrowth assay, and 6-27 times less than the frequencies of cells harbouring viral DNA measured by PCR-based assays. TILDA measurements strongly correlated with most HIV DNA assays. The size of the latent reservoir measured by TILDA was lower in subjects who initiated ART during the early compared to late stage of infection (p = 0.011). In untreated HIV disease, the frequency of CD4 + cells carrying latent but inducible HIV largely exceeded the frequency of actively producing cells, demonstrating that the majority of infected cells are transcriptionally silent even in the absence of ART. INTERPRETATIONS: Our results suggest that TILDA is a reproducible and sensitive approach to measure the frequency of productively and latently infected cells in clinical settings. We demonstrate that the latent reservoir represents a substantial fraction of all infected cells prior to ART initiation. RESEARCH IN CONTEXT: In this manuscript, we describe the development of a novel assay that measures the magnitude of the latent HIV reservoir, the main barrier to HIV eradication. This novel assay, termed TILDA for Tat/rev Induced Limiting Dilution Assay, requires only 10 ml of blood, does not necessitate extraction of viral nucleic acids, is highly reproducible, covers a wide dynamic range of reservoir sizes and can be completed in two days. As such, TILDA may represent an alternative to existing assays used to evaluate the efficacy of therapeutic strategies aimed at reducing the size of the latent HIV reservoir.

Association between first-year virological response to raltegravir and long-term outcomes in treatment-experienced patients with HIV-1 infection.

BACKGROUND: We explored the relationship between virological response in the first year of treatment and long-term outcomes in the BENCHMRK studies. METHODS: Patients failing antiretroviral treatment with 3-class resistant HIV-1 received double-blinded raltegravir (or placebo) with optimized background therapy (OBT) until week 156, followed by open-label raltegravir with OBT up to week 240. In this exploratory analysis of patients randomized to raltegravir, virological response over weeks 16-48 was categorized as continuous suppression (CS; viral RNA [vRNA] always <50 copies/ml), low-level viraemia (LLV; vRNA always <400 copies/ml, >50 copies/ml at least once), or not suppressed (NS; vRNA >400 copies/ml at least once). The association between these first-year vRNA response categories and baseline factors was analysed with univariate and multivariate models. Virological and immunological outcomes for years 2-5 were assessed by first-year vRNA response category (observed failure approach). RESULTS: Baseline vRNA, baseline CD4(+) T-cell count and rapid viral decay (vRNA <50 copies/ml between weeks 2-12) correlated with first-year vRNA response (P<0.001); only rapid viral decay remained significant by multiple regression. Virological response rates were similar in the LLV and CS groups and lowest in the NS group. CD4(+) T-cell count increased through week 240 in the CS and LLV groups. Time to loss of virological response (confirmed vRNA ≥400 copies/ml) through week 240 did not support as strong a difference between the LLV and CS groups (log-rank P=0.11) as previously reported through weeks 156 and 192 (P<0.05). CONCLUSIONS: Treatment-experienced patients on a raltegravir-based regimen with early LLV may have long-term virological and immunological benefit when their therapy is maintained.

Virologic resistance analysis from a phase 2 study of MK-5172 combined with pegylated interferon/ribavirin in treatment-naive patients with hepatitis C virus genotype 1 infection.

BACKGROUND: Virologic failure following treatment of hepatitis C virus (HCV) genotype 1 with direct-acting antiviral agents is often accompanied by the emergence of resistant variants. MK-5172 is an investigational once-daily protease inhibitor. We analyzed variants in treatment-naive noncirrhotic patients with virologic failure on MK-5172 (100-800 mg/day) plus pegylated interferon alfa/ribavirin (peg-IFN/RBV) during a phase 2 trial. METHODS: Population and selective clonal sequencing were performed at baseline and at virologic failure in the 4 MK-5172 dosing arms. MK-5172 activity was determined using a mutant replicon assay. RESULTS: Six of 266 (2.3%) MK-5172 recipients satisfied prespecified criteria for virologic failure, all with genotype 1a infection. Five patients with virologic failure were in the MK-5172 100-mg arm, including 4 patients with low plasma MK-5172 levels documented during triple therapy. Variants associated with >4-fold loss of potency were detected in 3 of the 4 patients with genotype 1a breakthrough while on MK-5172. The fifth patient had undetectable HCV-RNA levels at the end of triple therapy but subsequently broke through during the peg-IFN/RBV tail 16 weeks after completion of MK-5172. Three patients had D168 variants at virologic failure, including 2 with the D168A variant associated with a 95-fold loss of potency. The sole apparent relapse was actually a genotype 3a reinfection in the MK-5172 200-mg group. CONCLUSIONS: Virologic failure occurred uncommonly (6/266 [2.3%]) in MK-5172/peg-IFN/RBV recipients. The most prevalent treatment-emergent variants were detected at the D168 locus. D168A variants conferring approximately 2-log reduction in MK-5172 susceptibility emerged in 2 of the 4 evaluable patients with genotype 1a breakthrough. Clinical Trials Registration. NCT01353911.

Combination of vaniprevir with peginterferon and ribavirin significantly increases the rate of SVR in treatment-experienced patients with chronic HCV genotype 1 infection and cirrhosis.

BACKGROUND & AIMS: The combination of vaniprevir (a NS3/4A protease inhibitor) with peginterferon and ribavirin was shown to increase rates of sustained virologic response (SVR) significantly, compared with peginterferon and ribavirin alone, in treatment-experienced patients with chronic hepatitis C virus (HCV) genotype 1 infection without cirrhosis. We performed a blinded, randomized, controlled trial of the effects of vaniprevir with peginterferon and ribavirin in patients with cirrhosis who did not respond to prior therapy with peginterferon and ribavirin. METHODS: Treatment-experienced patients (88% white and 35% prior null responders) with HCV genotype 1 infection and compensated cirrhosis were assigned randomly to groups given vaniprevir (600 mg twice daily) with peginterferon and ribavirin for 24 weeks (n = 16), vaniprevir (600 mg twice daily) for 24 weeks with peginterferon and ribavirin for 48 weeks (n = 14), vaniprevir (300 mg twice daily) with peginterferon and ribavirin for 48 weeks (n = 15), vaniprevir (600 mg twice daily) with peginterferon and ribavirin for 48 weeks (n = 15), or placebo with peginterferon and ribavirin for 48 weeks (n = 14, control). Cirrhosis was documented by liver biopsy (84%) or noninvasive methods (16%). Before randomization, participants were stratified based on their historical response to peginterferon and ribavirin. RESULTS: In the primary analysis, SVR rates among patients in the respective vaniprevir groups were 9 of 15 (60.0%), 9 of 13 (69.2%), 8 of 15 (53.3%), and 10 of 13 (76.9%), compared with 2 of 14 (14.3%) in the control group (pairwise P values ≤ .016). Cirrhotic patients with null or partial responses to prior therapy achieved SVR less often than patients with prior breakthrough or relapse, although 42.1% of prior null responders in the vaniprevir groups achieved SVRs. Patients in the vaniprevir groups more frequently experienced mild-moderate nausea, vomiting, and diarrhea than controls; 5% developed grade 2 anemia compared with none in the control group (no patient developed grade 3 or 4 anemia). Among patients in the vaniprevir groups who experienced virologic failure, resistance-associated variants were detected predominantly at positions 155, 156, and 168 in the HCV protease gene. CONCLUSIONS: In a controlled phase 2B trial, vaniprevir with peginterferon and ribavirin significantly increased rates of SVR among treatment-experienced patients with chronic HCV genotype 1 infection, compared with re-treatment with peginterferon and ribavirin alone. Vaniprevir generally was well tolerated for up to 48 weeks in patients with compensated cirrhosis. ClinicalTrials.gov number, NCT00704405.

Analysis of boceprevir resistance associated amino acid variants (RAVs) in two phase 3 boceprevir clinical studies.

BACKGROUND: We investigated the frequency of RAVs among patients failing to achieve SVR in two clinical trials. We also investigated the impact of interferon responsiveness on RAVs and specific baseline RAVs relationship with boceprevir treatment failure. METHODS: Data are from 1020 patients enrolled into either SPRINT-2 or RESPOND-2; patients received a 4-week PR lead-in prior to receiving boceprevir or placebo. RAVs were analyzed via population-based sequence analysis of the NS3 protease gene (success rate of >90% at a virus level of ≥ 10,000IU/mL) RESULTS: The high SVR rate in patients who received boceprevir resulted in a low rate of RAVs; 7% was detected at baseline in all patients, which rose to 15% after treatment. However, RAVs were detected in 53% of patients that failed to achieve SVR, which declined to 22.8% 6-14 months following cessation of boceprevir therapy. Baseline RAVs alone were not predictive of virologic outcome; poor interferon responsiveness was highly predictive of non-SVR. RAVs were more frequently detected in poor interferon responders. CONCLUSIONS: We detected no association between the presence of baseline amino acid variants at boceprevir resistance-associated loci and outcome in the context of good IFN response.

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.

Efficacy and safety of raltegravir for treatment of HIV for 5 years in the BENCHMRK studies: final results of two randomised, placebo-controlled trials.

BACKGROUND: Two randomised, placebo-controlled trials-BENCHMRK-1 and BENCHMRK-2-investigated the efficacy and safety of raltegravir, an HIV-1 integrase strand-transfer inhibitor. We report final results of BENCHMRK-1 and BENCHMRK-2 combined at 3 years (the end of the double-blind phase) and 5 years (the end of the study). METHODS: Integrase-inhibitor-naive patients with HIV resistant to three classes of drug and who were failing antiretroviral therapy were enrolled. Patients were randomly assigned (2:1) to raltegravir 400 mg twice daily or placebo, both with optimised background treatment. Patients and investigators were masked to treatment allocation until week 156, after which all patients were offered open-label raltegravir until week 240. The primary endpoint was previously assessed at 16 weeks. We assessed long-term efficacy with endpoints of the proportion of patients with an HIV viral load of less than 50 copies per mL and less than 400 copies per mL, and mean change in CD4 cell count, at weeks 156 and 240. FINDINGS: 1012 patients were screened for inclusion. 462 were treated with raltegravir and 237 with placebo. At week 156, 51% in the raltegravir group versus 22% in the placebo group (non-completer classed as failure) had viral loads of less than 50 copies per mL, and 54% versus 23% had viral loads of less than 400 copies per mL. Mean CD4 cell count increase (analysed by an observed failure approach) was 164 cells per µL versus 63 cells per µL. After week 156, 251 patients (54%) from the raltegravir group and 47 (20%) from the placebo group entered the open-label raltergravir phase; 221 (47%) versus 44 (19%) completed the entire study. At week 240, viral load was less than 50 copies per mL in 193 (42%) of all patients initially assigned to raltegravir and less than 400 copies per mL in 210 (45%); mean CD4 cell count increased by 183 cells per µL. Virological failure occurred in 166 raltegravir recipients (36%) during the double-blind phase and in 17 of all patients (6%) during the open-label phase. The most common drug-related adverse events at 5 years in both groups were nausea, headache, and diarrhoea, and occurred in similar proportions in each group. Laboratory test results were similar in both treatment groups and showed little change after year 2. INTERPRETATION: Raltegravir has a favourable long-term efficacy and safety profile in integrase-inhibitor-naive patients with triple-class resistant HIV in whom antiretroviral therapy is failing. Raltegravir is an alternative for treatment-experienced patients, particularly those with few treatment options. FUNDING: Merck Sharp & Dohme.

Antiviral activity of boceprevir monotherapy in treatment-naive subjects with chronic hepatitis C genotype 2/3.

BACKGROUND & AIMS: To examine the antiviral activity of boceprevir, a hepatitis C virus (HCV) protease inhibitor, in HCV genotype (G) 2/3-infected patients. METHODS: We assessed boceprevir and telaprevir activity against an HCV G2 and G3 isolates enzyme panel, in replicon, and in phenotypic cell-based assays. Additionally, a phase I study evaluated the antiviral activity of boceprevir monotherapy (200mg BID, 400mg BID, or 400mg TID) vs. placebo for 14 days in HCV G2/3 treatment-naive patients. RESULTS: Boceprevir and telaprevir similarly inhibited G1 and G2 NS3/4A enzymes and replication in G1 and G2 replicon and cell-based assays. However, telaprevir demonstrated lower potency than boceprevir against HCV G3a enzyme (Ki=75 nM vs. 17 nM), in the G3a replicon assay (EC50=953 nM vs. 159 nM), and against HCV G3a NS3 isolates (IC50=3312 nM vs. 803 nM) in the cell-based assay. In HCV G2/3-infected patients, boceprevir (400 mg TID) resulted in a maximum mean decrease in HCV RNA of -1.60 log vs. -0.21 log with placebo. CONCLUSIONS: In vitro, boceprevir is more active than telaprevir against the HCV G3 NS3/4A enzyme in cell-based and biochemical assays and against G3 isolates in replicon assays. In HCV G2/3-infected treatment-naive patients, decreases in HCV RNA levels with boceprevir (400 mg TID) were comparable to those observed with the same dose in HCV treatment-experienced G1-infected patients.

Resistance-associated amino acid variants associated with boceprevir plus pegylated interferon-α2b and ribavirin in patients with chronic hepatitis C in the SPRINT-1 trial.

BACKGROUND: Resistance to direct-acting antivirals represents a new challenge in the treatment of chronic hepatitis C. METHODS: SPRINT-1 was a randomized study of treatment-naive patients with genotype (G) 1 hepatitis C infection (n=595) that evaluated the safety and efficacy of boceprevir (BOC) when added to pegylated interferon-α2b plus ribavirin (PR). Plasma samples collected at protocol-specified visits were analysed by population sequencing for detection of BOC-associated resistance-associated variants (RAVs). RESULTS: A total of 17/24 (71%) patients randomized to BOC with baseline RAVs achieved sustained virological response (SVR). V55A/I (n=14), Q41H (n=11) and T54S (n=9) were the most frequently detected polymorphisms at baseline. Seven non-SVR patients with baseline RAVs had V55A (relapse, n=3; breakthrough, n=1; and non-response, n=1) and/or R155K (non-response, n=2). In total, 63/144 (44%) patients with sequenced post-baseline samples (2 SVR, 61 non-SVR) had detectable RAVs after BOC treatment (G1a: R155K [39/49; 80%], V36M [37/49; 76%] and T54S [24/49; 49%]; G1b: T54S [3/11; 27%], T54A [4/11; 35%], A156S [2/11; 18%] and V170A [2/11; 18%]). RAV frequency varied according to the virological response: 90%, 67%, 27% and 37% of breakthrough, incomplete virological response, relapse and non-responder patients, respectively, had post-baseline RAVs present. Similar RAVs were identified in both the PR lead-in and no-lead-in arms and the frequency of post-baseline RAVs was highest in the low-dose ribavirin arm. CONCLUSIONS: SVR rates were not compromised among patients with RAVs at baseline; however, a lower starting mg/kg dose of ribavirin was associated with a higher frequency of post-baseline RAVs.