Fostemsavir in Adults with Multidrug-Resistant HIV-1 Infection.

BACKGROUND: Among some patients with human immunodeficiency virus type 1 (HIV-1) infection who have undergone multiple antiretroviral therapies and have limited options for treatment, new classes of antiretroviral drugs with novel mechanisms of action are needed. Fostemsavir is the prodrug of temsavir, a first-in-class investigational HIV-1 attachment inhibitor. METHODS: In this ongoing phase 3 trial in 23 countries, we enrolled patients with multidrug-resistant HIV-1 infection in two cohorts, according to their remaining treatment options. In the first cohort, we assigned (in a 3:1 ratio) patients who had the option of using at least one fully active, approved antiretroviral drug in at least one but no more than two antiretroviral classes to add either fostemsavir (at a dose of 600 mg twice daily) or placebo to their failing regimen for 8 days, followed by open-label fostemsavir plus optimized background therapy (randomized cohort). In the second cohort, patients who had no remaining antiretroviral options were started on open-label fostemsavir plus optimized background therapy on day 1 (nonrandomized cohort). The primary end point was the mean change in the HIV-1 RNA level from day 1 through day 8 in the randomized cohort. RESULTS: A total of 371 patients were treated, including 272 in the randomized cohort and 99 in the nonrandomized cohort. At day 8, the mean decrease in the HIV-1 RNA level was 0.79 log10 copies per milliliter in the fostemsavir group and 0.17 log10 copies in the placebo group (P<0.001). At week 48, a virologic response (HIV-1 RNA level, <40 copies per milliliter) had occurred in 54% of the patients in the randomized cohort and in 38% of those in the nonrandomized cohort; the mean increase in the CD4+ T-cell count was 139 cells per cubic millimeter and 64 cells per cubic millimeter, respectively. Adverse events led to the discontinuation of fostemsavir in 7% of the patients. In the randomized cohort, glycoprotein 120 (gp120) substitutions were found in 20 of 47 patients (43%) with virologic failure. CONCLUSIONS: In patients with multidrug-resistant HIV-1 infection with limited therapy options, those who received fostemsavir had a significantly greater decrease in the HIV-1 RNA level than those who received placebo during the first 8 days. Efficacy was sustained through 48 weeks. (Funded by Bristol-Myers Squibb and GSK/ViiV Healthcare; BRIGHTE ClinicalTrials.gov number, NCT02362503.).

Week 96 Genotypic and Phenotypic Results of the Fostemsavir Phase 3 BRIGHTE Study in Heavily Treatment-Experienced Adults Living with Multidrug-Resistant HIV-1.

In the phase 3 BRIGHTE study in heavily treatment-experienced adults with multidrug-resistant HIV-1, fostemsavir plus optimized background therapy (OBT) resulted in sustained rates of virologic suppression through 96 weeks. HIV-1 RNA <40 copies/mL was achieved in 163/272 (60%) Randomized Cohort (RC) participants (with 1 or 2 remaining approved fully active antiretrovirals) and 37/99 (37%) Non-randomized Cohort (NRC) participants (with 0 fully active antiretrovirals). Here we report genotypic and phenotypic analyses of HIV-1 samples from 63/272 (23%) RC participants and 49/99 (49%) NRC participants who met protocol-defined virologic failure (PDVF) criteria through Week 96. The incidence of PDVF was as expected in this difficult-to-treat patient population and, among RC participants, was comparable regardless of the presence of predefined gp120 amino acid substitutions that potentially influence phenotypic susceptibility to temsavir (S375H/I/M/N/T, M426L, M434I, M475I) or baseline temsavir 50% inhibitory concentration fold change (IC50 FC). The incidence of PDVF was lower among participants with higher overall susceptibility score to newly used antiretrovirals (OSS-new), indicating that OSS-new may be a preferred predictor of virologic outcome in heavily treatment-experienced individuals. Predefined gp120 substitutions, most commonly M426L or S375N, were emergent on treatment in 24/50 (48%) RC and 33/44 (75%) NRC participants with PDVF, with related increases in temsavir IC50 FC. In BRIGHTE, PDVF was not consistently associated with treatment-emergent genotypic or phenotypic changes in susceptibility to temsavir or to antiretrovirals in the initial OBT. Further research will be needed to identify which factors are most likely to contribute to virologic failure in this heavily treatment-experienced population (ClinicalTrials.gov, NCT02362503).

Prevalence of gp160 polymorphisms known to be related to decreased susceptibility to temsavir in different subtypes of HIV-1 in the Los Alamos National Laboratory HIV Sequence Database.

BACKGROUND: Fostemsavir, a prodrug of the gp120-directed attachment inhibitor temsavir, is indicated for use in heavily treatment-experienced individuals with MDR HIV-1. Reduced susceptibility to temsavir in the clinic maps to discrete changes at amino acid positions in gp160: S375, M426, M434 and M475. OBJECTIVES: To query the Los Alamos National Laboratory (LANL) HIV Sequence Database for the prevalence of polymorphisms at gp160 positions of interest. METHODS: Full-length gp160 sequences (N = 7560) were queried for amino acid polymorphisms relative to the subtype B consensus at positions of interest; frequencies were reported for all sequences and among subtypes/circulating recombinant forms (CRFs) with ≥10 isolates in the database. RESULTS: Among 239 subtypes in the database, the 5 most prevalent were B (n = 2651, 35.1%), C (n = 1626, 21.5%), CRF01_AE (n = 674, 8.9%), A1 (n = 273, 3.6%) and CRF02_AG (n = 199, 2.6%). Among all 7560 sequences, the most prevalent amino acids at positions of interest (S375, 73.5%; M426, 82.1%; M434, 88.2%; M475, 89.9%) were the same as the subtype B consensus. Specific polymorphisms with the potential to decrease temsavir susceptibility (S375H/I/M/N/T/Y, M426L/P, M434I/K and M475I) were found in <10% of isolates of subtypes D, G, A6, BC, F1, CRF07_BC, CRF08_BC, 02A, CRF06_cpx, F2, 02G and 02B. S375H and M475I were predominant among CRF01_AE (S375H, 99.3%; M475I, 76.3%; consistent with previously reported low temsavir susceptibility of this CRF) and 01B (S375H, 71.7%; M475I, 49.5%). CONCLUSIONS: Analysis of the LANL HIV Sequence Database found a low prevalence of gp160 amino acid polymorphisms with the potential to reduce temsavir susceptibility overall and among most of the common subtypes.

Susceptibility of global HIV-1 clinical isolates to fostemsavir using the PhenoSense® Entry assay.

BACKGROUND: Fostemsavir is a prodrug of a first-in-class HIV-1 attachment inhibitor, temsavir, that binds to gp120 and blocks attachment to the host-cell CD4 receptor, preventing entry and infection of the target cell. Previous studies using a limited number of clinical isolates showed that there was intrinsic variability in their susceptibility to temsavir. OBJECTIVES: Here, an analysis was performed using all clinical isolates analysed in the Monogram Biosciences PhenoSense® Entry assay as part of the development programme. METHODS: In total, 1337 individual envelopes encompassing 20 different HIV-1 subtypes were examined for their susceptibility to temsavir. However, only seven subtypes (B, C, F1, A, [B, F1], BF and A1) were present more than five times, with subtype B (881 isolates) and subtype C (156 isolates) having the largest numbers. RESULTS: As expected, variability in susceptibility was observed within all subtypes. However, for the great majority of these viruses, temsavir was highly potent, with most viruses exhibiting IC50s <10 nM. One exception was CRF01_AE viruses, where all five isolates exhibited IC50s >100 nM. For the 607 isolates where tropism data were available, geometric mean temsavir IC50 values were remarkably similar for CCR5-, CXCR4- and dual mixed-tropic envelopes from infected individuals. CONCLUSIONS: These data show that HIV-1 viruses from most subtypes are highly susceptible to temsavir and that temsavir susceptibility is independent of tropism.

The Sensitivity of HIV-1 gp120 Polymorphs to Inhibition by Temsavir Correlates to Temsavir Binding On-rate.

Temsavir binds directly to the HIV-1 envelope glycoprotein gp120 and selectively inhibits interactions between HIV-1 and CD4 receptors. Previous studies identified gp120 amino acid positions where substitutions are associated with reduced susceptibility to temsavir. The mechanism by which temsavir susceptibility is altered in these envelope glycoproteins was evaluated. Pseudoviruses encoding gp120 substitutions alone (S375H/I/M/N, M426L, M434I, M475I) or in combination (S375H + M475I) were engineered on a wild-type JRFL background. Temsavir-gp120 and CD4-gp120 binding kinetics and ability of temsavir to block CD4-gp120 binding were evaluated using the purified polymorphic gp120 proteins and a Creoptix® WAVE Delta grating-coupled interferometry system. The fold-change in half-maximal inhibitory concentration (IC50) in JRFL-based pseudoviruses containing the aforementioned polymorphisms relative to that of wild-type ranged from 4-fold to 29,726-fold, while temsavir binding affinity for the polymorphic gp120 proteins varied from 0.7-fold to 73.7-fold relative to wild-type gp120. Strong correlations between temsavir IC50 and temsavir binding affinity (r=0.7332; P=0.0246) as well as temsavir binding on-rate (r=-0.8940; P=0.0011) were observed. Binding affinity of gp120 proteins for CD4 varied between 0.4-fold and 3.1-fold compared with wild-type gp120; no correlations between temsavir IC50 and CD4 binding kinetic parameters were observed. For all polymorphic gp120 proteins, temsavir was able to fully block CD4 binding; 3 polymorphs required higher temsavir concentrations. Loss of susceptibility to temsavir observed for gp120 polymorphisms strongly correlated with reductions in temsavir binding on-rate. Nonetheless, temsavir retained the ability to fully block CD4-gp120 engagement given sufficiently high concentrations.

Characterization of Clinical Envelopes With Lack of Sensitivity to the HIV-1 Inhibitors Temsavir and Ibalizumab.

Previous data suggest a lack of cross-resistance between the gp120-directed attachment inhibitor temsavir (active moiety of fostemsavir) and the CD4-directed post-attachment inhibitor ibalizumab. Recently, analysis of HIV-1 envelopes with reduced sensitivity to both inhibitors was undertaken to determine whether they shared genotypic correlates of resistance. Sequences from 2 envelopes with reduced susceptibility to both agents were mapped onto a temsavir-bound gp120 structure. Residues within 5.0 Å of the temsavir binding site were evaluated using reverse genetics. Broader applicability and contextual determinants of key substitutions were further assessed using envelopes from participants in the phase 3 BRIGHTE study. Temsavir sensitivity was measured by half-maximal inhibitory concentration (IC50) and ibalizumab sensitivity by IC50 and maximum percent inhibition (MPI). One envelope required substitutions of E113D and T434M for full restoration of temsavir susceptibility. Neither substitution nor their combination affected ibalizumab sensitivity. However, in the second envelope, an E202 substitution (HXB2, T202) was sufficient for observed loss of susceptibility to both inhibitors. One BRIGHTE participant with no ibalizumab exposure had an emergent K202E substitution at protocol-defined virologic failure, with reduced sensitivity to both inhibitors. Introducing T202E into previously susceptible clinical isolates reduced temsavir potency by ≥40-fold and ibalizumab MPI from >99% to ∼80%. Interestingly, introduction of the gp120 V5 region from a highly ibalizumab-susceptible envelope mitigated the E202 effect on ibalizumab but not temsavir. A rare HIV-1 gp120 E202 mutation reduced temsavir susceptibility, and depending on sequence context, could result in reduced susceptibility to ibalizumab.

Week 240 Efficacy and Safety of Fostemsavir Plus Optimized Background Therapy in Heavily Treatment-Experienced Adults with HIV-1.

INTRODUCTION: Efficacy and safety of the attachment inhibitor fostemsavir + optimized background therapy (OBT) were evaluated through 48 and 96 weeks in the phase 3 BRIGHTE trial in heavily treatment-experienced (HTE) adults failing their current antiretroviral regimen. Here, we report 240-week efficacy and safety of fostemsavir + OBT in adults with multidrug-resistant human immunodeficiency virus (HIV)-1 in BRIGHTE. METHODS: Heavily treatment-experienced adults failing their current regimen entered the randomized cohort (RC; 1-2 fully active antiretrovirals available) or non-randomized cohort (NRC; no fully active antiretrovirals available) and received open-label fostemsavir + OBT (starting Day 8 in RC and Day 1 in NRC). Endpoints included proportion with virologic response (HIV-1 RNA < 40 copies/mL, Snapshot), immunologic efficacy, and safety. RESULTS: At Week 240, 45% and 22% of the RC and NRC, respectively, had virologic response (Snapshot); 7% of the RC and 5% of the NRC had missing data due to coronavirus disease 2019 (COVID-19)-impacted visits. In the observed analysis, 82% of the RC and 66% of the NRC had virologic response. At Week 240, mean change from baseline in CD4+ T-cell count was 296 cells/mm3 (RC) and 240 cells/mm3 (NRC); mean CD4+/CD8+ ratio increased between Weeks 96 and 240 (RC 0.44 to 0.60; NRC 0.23 to 0.32). Between Weeks 96 and 240, four participants discontinued for adverse events, one additional participant experienced a drug-related serious adverse event, and six deaths occurred (median last available CD4+ T-cell count, 3 cells/mm3). COVID-19-related events occurred in 25 out of 371 participants; all resolved without incident. CONCLUSION: Through ~5 years, fostemsavir + OBT demonstrated durable virologic and immunologic responses with no new safety concerns between Weeks 96 and 240, supporting this regimen as a key therapeutic option for HTE people with multidrug-resistant HIV-1. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02362503.

Discovery of novel P3-oxo inhibitor of hepatitis C virus NS3/4A serine protease.

A novel series of P3 oxo-modified macrocyclic hepatitis C virus NS3/4A serine protease inhibitor was designed, synthesized and biologically evaluated. The hydroxy-substituted inhibitor 10 demonstrated high potency in genotype 1a and 1b replicon and in the panel of HCV protease mutants. Interestingly, the t-butyl carbonate analog 9c, while not the most potent one in this series, exhibited a virtually flat potency profile in the panel of HCV protease mutants, thus providing opportunity for further optimization.

Clinical evidence for a lack of cross-resistance between temsavir and ibalizumab or maraviroc.

BACKGROUND: Temsavir (TMR), the active agent of the gp120-directed attachment inhibitor fostemsavir (FTR), the CD4-directed attachment inhibitor ibalizumab (IBA), and the CCR5 antagonist maraviroc (MVC) are antiretroviral agents that target steps in HIV-1 viral entry. Although mechanisms of inhibition of the three agents are different, it is important to understand whether there is potential for cross-resistance between these agents, as all involve interactions with gp120. METHODS: Envelopes derived from plasma samples from participants in the BRIGHTE study who experienced protocol-derived virologic failure (PDVF) and were co-dosed with FTR and either IBA or MVC were analyzed for susceptibility to the agents. Also, CCR5-tropic MVC-resistant envelopes from the MOTIVATE trials were regenerated and studies were performed to understand whether susceptibility to multiple agents were linked. RESULTS: The cloned envelopes exhibited reduced susceptibility to TMR and resistance to the co-dosed agent. At PDVF, emergent or preexisting amino acid substitutions were present at TMR positions of interest. When amino acid substitutions at these positions were reverted to the consensus sequence, full susceptibility to TMR was restored without effecting resistance to the co-dosed agent. In addition, five envelopes from MOTIVATE were regenerated and exhibited R5-tropic-MVC-resistance. Only one exhibited reduced susceptibility to TMR and it contained an M426L polymorphism. When reverted to 426M, full sensitivity for TMR was restored, but it remained MVC resistant. CONCLUSION: The data confirm that decreased susceptibility to TMR and resistance to IBA or MVC are not linked and that there is no cross-resistance between either of these two agents and FTR.

Safety and efficacy of the HIV-1 attachment inhibitor prodrug fostemsavir in heavily treatment-experienced individuals: week 96 results of the phase 3 BRIGHTE study.

BACKGROUND: Fostemsavir, a prodrug of the first-in-class attachment inhibitor, temsavir, is indicated for heavily treatment-experienced individuals with multidrug-resistant HIV-1. We previously reported superior efficacy of fostemsavir versus placebo in the randomised cohort of the BRIGHTE study after 8-day functional monotherapy (primary endpoint); here we report planned interim analyses through week 96. METHODS: BRIGHTE (NCT02362503) is an ongoing multicentre, two-cohort, phase 3 trial, done at 108 centres in 22 countries. We enrolled heavily treatment-experienced adults (≥18 years) failing antiretroviral therapy (HIV-1 RNA ≥400 copies per mL) into two cohorts: the randomised cohort, in which patients with one or two fully active antiretrovirals remaining received oral fostemsavir (600 mg twice a day) or placebo in combination with their failing regimen for 8 days, followed by fostemsavir plus optimised background therapy; or the non-randomised cohort, in which patients with no remaining antiretroviral options received oral fostemsavir (600 mg twice a day) plus optimised background therapy from day 1. Endpoints for the week 96 interim analyses included the proportions of participants with plasma HIV-1 RNA of less than 40 copies per mL, changes from baseline in CD4 cell counts, and the frequency of adverse events, adverse events leading to discontinuation, and deaths. The intention-to-treat exposed population and the safety population both included all participants who received at least one dose of study treatment. The response rates (proportion of participants with HIV-1 RNA <40 copies per mL) in the intention-to-treat exposed population were calculated via snapshot analysis at weeks 24, 48, and 96. FINDINGS: Between Feb 23, 2015, and Aug 11, 2016, 371 participants were enrolled and treated, of which 272 participants were in the randomised cohort and 99 in the non-randomised cohort. 320 (86%) of 371 reported a history of AIDS. In the randomised cohort, rates of virological suppression (HIV-1 RNA <40 copies per mL) increased from 53% (144 of 272) at week 24 to 60% (163 of 272) at week 96. Response rates in the non-randomised cohort were 37% (37 of 99) at week 24 and week 96. Mean increases in CD4 counts from baseline at week 96 were 205 cells per µL (SD 191) in the randomised cohort and 119 cells per µL (202) in the non-randomised cohort. Mean CD4/CD8 ratio increased from 0·20 at baseline to 0·44 at week 96 in the randomised cohort. Few adverse events led to discontinuation (26 [7%] of 371). 12 (4%) of 272 people in the randomised cohort and 17 (17%) of 99 in the non-randomised cohort died; the median baseline CD4 count for participants who died was 11 cells per µL. INTERPRETATION: In heavily treatment-experienced individuals with advanced HIV-1 disease and limited treatment options, fostemsavir-based antiretroviral regimens were generally well tolerated and showed a distinctive trend of increasing virological and immunological response rates through 96 weeks; these findings support fostemsavir as a treatment option for this vulnerable population. FUNDING: ViiV Healthcare.

Potent inhibitors of HIV-1 integrase display a two-step, slow-binding inhibition mechanism which is absent in a drug-resistant T66I/M154I mutant.

Two-metal binding HIV-1 integrase inhibitors (INIs) are potent inhibitors of HIV-1 in vitro and in patients. We report here for the first time the kinetics of inhibition of integrase-catalyzed strand transfer. First, the IC(50) values for each of six structurally distinct INIs decreased when a preincubation was included: S-1360 (1.3 microM vs 0.12 microM), L-731,988 (130 nM vs 9 nM), L-870,810 (130 nM vs 4 nM), raltegravir (300 nM vs 9 nM), elvitegravir (90 nM vs 6 nM), and GSK364735 (90 nM vs 6 nM). When reactions with these INIs were initiated with integrase, progress curve analyses indicated time-dependent inhibition, which could be fitted to a two-step mechanism of binding. Overall fitted K(i) values matched the IC(50) values measured with a preincubation: S-1360 (0.17 microM), L-731,988 (34 nM), L-870,810 (2.4 nM), raltegravir (10 nM), elvitegravir (4.0 nM), and GSK364735 (2.5 nM). To begin to understand the mechanism for this slow onset of inhibition and its possible impact on drug resistance, studies of resistance mutations were initiated. T66I/M154I exhibited little if any time-dependent inhibition by any of the six INIs, as measured by differences in potency upon preincubation or by progress curve analysis. These data demonstrate that slow binding is a signature of two-metal binding INIs, and that the second slow step is required for full potency. We discuss a possible structural explanation of the second slow step of inhibition and also the relationship between loss of time-dependent inhibition and drug resistance of this important new class of HIV-1 antiretroviral drugs.

Safety, efficacy, and dose response of the maturation inhibitor GSK3532795 (formerly known as BMS-955176) plus tenofovir/emtricitabine once daily in treatment-naive HIV-1-infected adults: Week 24 primary analysis from a randomized Phase IIb trial.

GSK3532795 (formerly known as BMS-955176) is a second-generation maturation inhibitor targeting a specific Gag cleavage site between capsid p24 and spacer peptide 1 of HIV-1. Study 205891 (previously AI468038) investigated the efficacy, safety, and dose response of GSK3532795 in treatment-naive, HIV-1-infected participants. Study 205891 (NCT02415595) was a Phase IIb, randomized, active-controlled, double-blind, international trial. Participants were randomized 1:1:1:1 to one of three GSK3532795 arms at doses 60 mg, 120 mg or 180 mg once daily (QD), or to efavirenz (EFV) at 600 mg QD, each in combination with tenofovir disoproxil fumarate and emtricitabine (TDF/FTC) (300/200 mg QD). Primary endpoint was proportion of participants with plasma HIV-1 RNA <40 copies/mL at Week 24. Between May 2015 and May 2016, 206 participants received treatment. At Week 24, 76-83% participants receiving GSK3532795 and 77% receiving EFV achieved HIV-1 RNA <40 copies/mL. Fifteen participants receiving GSK3532795 and one receiving EFV met resistance testing criteria; 10/15 receiving GSK3532795 had emergent substitutions at reverse transcriptase positions M184, and one at position K65, while the participant receiving EFV did not have any nucleoside reverse transcriptase inhibitor (NRTI)/non-NRTI mutations. EFV, relative to GSK3532795, had more serious adverse events (9% versus 5%) and adverse events leading to discontinuation (17% versus 5%). However, 3-4-fold higher rates of gastrointestinal adverse events were observed with GSK3532795 relative to EFV. GSK3532795 combined with TDF/FTC is efficacious with 24 weeks of therapy. However, GSK3532795 showed a higher rate of gastrointestinal intolerability and treatment-emergent resistance to the NRTI backbone relative to EFV. Trial registration: ClinicalTrials.gov NCT02415595.

A Phenotypic High-Throughput Screen with RSV-Infected Primary Human Small Airway Epithelial Cells (SAECs).

Respiratory syncytial virus (RSV) is a commonly occurring pathogen that can cause severe disease in children, the elderly, and immunocompromised individuals with a large, unmet clinical need. We developed a high-throughput, primary cell-based antiviral RSV assay to enable identification of small molecules using cytopathic effect (CPE) as a phenotypic end point. To provide increased biological relevance, we developed our assay with primary human small airway epithelial cells (SAECs), which originate from known sites of RSV infection and replication instead of a more traditional immortalized cell line. Using purchased low-passage cells, cost-effective large-scale culture methods were developed to provide assay-ready frozen SAECs. A high-throughput screening campaign using the GSK Screening Collection was performed. The screen was executed in 384-well plates over a 12-week period with an average Z' of 0.5. The screen yielded 17 post-entry hits with activity in the primary cells, which were not active in immortalized cells. Potencies for this class of compounds were equal between the primary and immortalize cell lines. For entry inhibitors, the number was much lower, with increased potency observed in immortalized cells. This is the first known use of frozen primary human cells for an RSV high-throughput screening phenotypic campaign.

GSK983: a novel compound with broad-spectrum antiviral activity.

GSK983, a novel tetrahydrocarbazole, inhibits the replication of a variety of unrelated viruses in vitro with EC(50) values of 5-20 nM. Both replication of the adenovirus Ad-5 and the polyoma virus SV-40, and episomal maintenance of human papillomaviruses (HPV) and Epstein-Barr virus (EBV) are susceptible to GSK983. The compound does not inhibit all viruses; herpes simplex virus (HSV-1), human immunodeficiency virus (HIV), and lytic replication of EBV were not susceptible at concentrations below 1 microM. GSK983 does inhibit the growth of cell lines immortalized by HTLV-1, EBV, HPV, SV40 and Ad-5, with EC(50) values in the range of 10-40 nM. Depending on the cell line, the compound induces either apoptosis or cytostasis at concentrations over 20 nM. GSK983 also inhibits cell lines immortalized by non-viral mechanisms, but has little effect on primary cells. The CC(50) values for keratinocytes, fibroblasts, lymphocytes, endothelial, and bone marrow progenitor cells are all above 10 microM. The pattern of inhibition, which includes diverse viruses as well as growth of immortalized cells of varied origins, suggests the target is a host cell protein, rather than a viral protein. Preliminary mechanism studies indicate that GSK983 acts by inducing a subset of interferon-stimulated genes.

The naphthyridinone GSK364735 is a novel, potent human immunodeficiency virus type 1 integrase inhibitor and antiretroviral.

The naphthyridinone GSK364735 potently inhibited recombinant human immunodeficiency virus type 1 (HIV-1) integrase in a strand transfer assay (mean 50% inhibitory concentration +/- standard deviation, 8 +/- 2 nM). As expected based on the structure of the drug, it bound competitively with another two-metal binding inhibitor (Kd [binding constant], 6 +/- 4 nM). In a number of different cellular assays, GSK364735 inhibited HIV replication with potency at nanomolar concentrations (e.g., in peripheral blood mononuclear cells and MT-4 cells, 50% effective concentrations were 1.2 +/- 0.4 and 5 +/- 1 nM, respectively), with selectivity indexes of antiviral activity versus in-assay cytotoxicity of at least 2,200. When human serum was added, the antiviral potency decreased (e.g., a 35-fold decrease in the presence of 100% human serum was calculated by extrapolation from the results of the MT-4 cell assay). In cellular assays, GSK364735 blocked viral DNA integration, with a concomitant increase in two-long-terminal-repeat circles. As expected, this integrase inhibitor was equally active against wild-type viruses and mutant viruses resistant to approved drugs targeting either reverse transcriptase or protease. In contrast, some but not all viruses resistant to other integrase inhibitors were resistant to GSK364735. When virus was passaged in the presence of the inhibitor, we identified resistance mutations within the integrase active site that were the same as or similar to mutations arising in response to other two-metal binding inhibitors. Finally, either additive or synergistic effects were observed when GSK364735 was tested in combination with approved antiretrovirals (i.e., no antagonistic effects were seen). Thus, based on all the data, GSK364735 exerted potent antiviral activity through the inhibition of viral DNA integration by interacting at the two-metal binding site within the catalytic center of HIV integrase.

The 5' untranslated region of GB virus B shows functional similarity to the internal ribosome entry site of hepatitis C virus.

Since its characterization in 1995, there has been increasing interest in the significance of GB virus B (GBV-B) due to its close phylogenetic relationship to hepatitis C virus (HCV). The genome of GBV-B is similar in length and organization to that of HCV and the two viruses share sequence similarity in their 5' untranslated regions (5'UTR). A secondary structure model of the GBV-B 5'UTR has been proposed by comparative sequence analysis with HCV. The highly conserved secondary structure, present in HCV and the pestiviruses, is also present in the 5'UTR of GBV-B. Translation of the HCV polyprotein initiates via an internal ribosome entry site (IRES) and it is proposed that the GBV-B UTR may function in a similar manner. Dicistronic reporter constructs were made to investigate the function of the GBV-B 5'UTR. Mutational analysis and in vitro translation experiments demonstrate that GBV-B initiates translation via an IRES.