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

High HIV-1 viremia and low anti-Env antibody responses are associated with delayed treatment response to fostemsavir in highly treatment-experienced individuals

Fostemsavir (FTR) is an approved first-in-class small molecule Env antagonist for treating multi-drug resistant (MDR) HIV-1 infection. In the BRIGHTE study, viral suppression rates in heavily treatment-experienced people with HIV (PWH) increased from week 48 through week 96. Factors that contribute to this late response are not well understood. Given FTR's ability to stabilize a native HIV-1 envelope trimer conformational state, we examined anti-HIV humoral immune responses in the BRIGHTE study to explore how evolving antibody responses in the presence of drug correlate with delayed viral suppression. 16 BRIGHTE study participants (ppt) were selected based on their time to first viremic suppression: eight early (EVS) and eight late viral suppressors (LVS). Immune responses were also analyzed in eight ppt from the SAILING study that evaluated dolutegravir. Anti-HIV Env IgG titer, cell-free and cell-to-cell neutralization activity, FcγRIIa- and FcγRIIIa-signaling, and plasma cytokines at weeks 0, 4 and 108 were examined and correlated with clinical variables associated with treatment response. FTR treatment did not significantly enhance antibody responses against reference strain of HIV in LVS compared to EVS. However, at baseline, LVS had significantly lower anti-HIV IgG titers, higher VL, lower CD4+ T-cell counts and experienced greater increases in CD4+ T-cell counts than EVS. Additionally, IL-8 levels were increased in LVS vs. EVS at treatment initiation. In comparison, SAILING ppt showed increased FcγRIIa signaling during drug treatment compared to the FTR groups. Further studies will determine if pre-treatment characteristics influence timing to viral suppression in FTR-treated individuals with MDR-HIV.

Immunological and virological response to fostemsavir in routine US clinical care: An OPERA cohort study

OBJECTIVES

Fostemsavir is a novel attachment inhibitor used with other antiretrovirals in heavily treatment-experienced (HTE) adults with multidrug-resistant HIV-1. Real-world immunological and virological responses were assessed in individuals starting fostemsavir in the OPERA cohort.

METHODS

Among adults with HIV-1 starting fostemsavir between 2 July 2020 and 1 September 2022, 6-month and 12-month changes in CD4 T-cell count and CD4%, and maintenance/achievement of viral load (VL) <50 copies/mL were described and stratified by baseline VL (suppressed: <50 copies/mL; viraemic: ≥50 copies/mL) and CD4 count (high: ≥350 cells/μL; low: <350 cells/μL).

RESULTS

Of 182 individuals starting fostemsavir, 64% were viraemic (34% low CD4, 30% high CD4) and 36% were suppressed (16% low CD4, 20% high CD4). The suppressed/low CD4 group had the largest median increases in CD4 count (6-month: 30 cells/μL [interquartile range {IQR} 9-66], 12-month: 66 cells/μL [IQR 17-125]), and CD4% (6-month: 1.0% [IQR -0.3-2.8], 12-month: 1.9% [IQR 1.3-3.9]). Regardless of baseline VL, those with a high baseline CD4 count experienced a greater variability in immunological response than those with low CD4 counts (12-month standard deviation range 172-231 cells/μL vs. 69-90 cells/μL). VL <50 copies/mL was maintained in most suppressed individuals; nearly half of the viraemic/high CD4 group and a third of the viraemic/low CD4 group achieved a VL <50 copies/mL at either timepoint.

CONCLUSIONS

After 6 or 12 months of fostemsavir use, virological response was low in viraemic individuals, although most suppressed individuals did maintain suppression. While immunological response varied across individuals, virologically suppressed HTE individuals with low CD4 counts may benefit from immunological improvements with fostemsavir.

Fostemsavir resistance in clinical context: a narrative review

Fostemsavir, a prodrug of the first-in-class gp120-directed attachment inhibitor temsavir, is indicated in combination with other antiretrovirals for the treatment of multidrug-resistant HIV-1 in adults who are heavily treatment-experienced (HTE). Temsavir binds to HIV-1 gp120, close to the CD4 binding site, preventing the initial interaction of HIV-1 with CD4 on the host cell. Amino acid substitutions at four positions in gp120 have been identified as important determinants of viral susceptibility to temsavir (S375H/I/M/N/T/Y, M426L/P, M434I/K, M475I), with a fifth position (T202E) recently described. For most currently circulating group M HIV-1 subtypes, the prevalence of these resistance-associated polymorphisms (RAPs) is low. As with many other antiretrovirals, the impact of RAPs is modified by other changes in the target molecule. Different regions of gp120 interact to modify the temsavir binding pocket, with multiple amino acids playing a role in determining susceptibility. Extensive variability of HIV-1 gp120 means the susceptibility of clinical isolates to temsavir is also highly variable. Importantly, in vitro measurement of the susceptibility of clinical isolates to temsavir does not necessarily capture the range of susceptibilities of the heterogeneous mix of viruses generally present in each isolate. Due to these factors and limited phenotypic clinical data, thus far, no relevant phenotypic cutoff or genotypic algorithms have been derived that reliably predict response to fostemsavir-based therapy in individuals who are HTE; therefore, pre-treatment temsavir resistance testing may be of limited benefit. In the phase III BRIGHTE study, re-suppression after virologic failure was observed in some participants despite treatment-emergent genotypic and/or phenotypic evidence of reduced temsavir susceptibility, and substantial CD4+ T-cell count increases occurred even among participants with HIV-1 RNA ⩾40 copies/mL at Week 240. Clinical management of people who are HTE and experience virologic failure during treatment with fostemsavir-based regimens requires an individualized approach with consideration of potential benefits beyond virologic suppression.

Heavily treatment-experienced patients with HIV: are new mechanisms of action enough?

Antiretroviral (ARV) drug resistance poses a threat to ending the HIV epidemic. As the rates of integrase resistance continue to increase globally, the availability of options for HIV treatment becomes limited. Heavily treatment-experienced (HTE) people with HIV (PWH) are limited to two or fewer available fully active ARV classes and are more likely to have an AIDS-defining event. Appropriate identification and management of HTE PWH is crucial to improving patient outcomes and reducing the future spread of drug-resistant HIV. As treatment options become more limited owing to drug resistance, the availability of more potent drugs with a marked increase in virologic suppression is needed in the current ART era. The purpose of this narrative review is to review the identification of HTE PWH, novel mechanisms of resistance, and management of HTE PWH in resource-rich and resource-limited settings using novel ARVs and combination ART.

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. 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.

Mechanism of action, resistance, interaction, pharmacokinetics, pharmacodynamics, and safety of fostemsavir

The Food and Drug Administration (FDA) has licensed many antiretroviral medications to treat human immunodeficiency virus type 1 (HIV-1), however, treatment options for people with multi-drug resistant HIV remain limited. Medication resistance, undesirable effects, prior tolerance, and previous interlacement incapacity to deliver new drug classes all lead to the requirement for new medication classes and drug combination therapy. Fostemsavir (FTR) is a new CD-4 attachment inhibitor medicine that was recently authorized by the United States FDA to treat HIV-1. In individuals with multidrug-resistant (MDR) HIV-1, FTR is well tolerated and virologically active. According to recent investigations, drug combination therapy can positively affect MDR-HIV. The mechanism of action, resistance, interaction, pharmacokinetics, pharmacodynamics, and safety of FTR has been highlighted in this review.