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).

Long-term efficacy and safety of fostemsavir among subgroups of heavily treatment-experienced adults with HIV-1

OBJECTIVES

The aim of this study was to understand how demographic and treatment-related factors impact responses to fostemsavir-based regimens.

DESIGN

BRIGHTE is an ongoing phase 3 study evaluating twice-daily fostemsavir 600 mg and optimized background therapy (OBT) in heavily treatment-experienced individuals failing antiretroviral therapy with limited treatment options (Randomized Cohort 1-2 and Nonrandomized Cohort 0 fully active antiretroviral classes).

METHODS

Virologic response rates (HIV-1 RNA <40 copies/ml, Snapshot analysis) and CD4+ T-cell count increases in the Randomized Cohort were analysed by prespecified baseline characteristics (age, race, sex, region, HIV-1 RNA, CD4+ T-cell count) and viral susceptibility to OBT. Safety results were analysed by baseline characteristics for combined cohorts (post hoc).

RESULTS

In the Randomized Cohort, virologic response rates increased between Weeks 24 and 96 across most subgroups. Virologic response rates over time were most clearly associated with overall susceptibility scores for new OBT agents (OSS-new). CD4+ T-cell count increases were comparable across subgroups. Participants with baseline CD4+ T-cell counts less than 20 cells/μl had a mean increase of 240 cells/μl. In the safety population, more participants with baseline CD4+ T-cell counts less than 20 vs. at least 200 cells/μl had grade 3/4 adverse events [53/107 (50%) vs. 24/96 (25%)], serious adverse events [58/107 (54%) vs. 25/96 (26%)] and deaths [16/107 (15%) vs. 2/96 (2%)]. There were no safety differences by other subgroups.

CONCLUSION

Week 96 results for BRIGHTE demonstrate comparable rates of virologic and immunologic response (Randomized Cohort) and safety (combined cohorts) across subgroups. OSS-new is an important consideration when constructing optimized antiretroviral regimens for heavily treatment-experienced individuals with limited remaining treatment options.