Characterization of the Drug Resistance Profiles of Integrase Strand Transfer Inhibitors in Simian Immunodeficiency Virus SIVmac239

Drug resistance emergence in macaques administered cabotegravir long-acting for pre-exposure prophylaxis during acute SHIV infection

A long-acting injectable formulation of the HIV integrase inhibitor cabotegravir (CAB-LA) is currently in clinical development for PrEP. Although the long plasma half-life of CAB-LA is an important attribute for PrEP, it also raises concerns about drug resistance emergence if someone becomes infected with HIV, or if PrEP is initiated during undiagnosed acute infection. Here we use a macaque model of SHIV infection to model risks of drug resistance to CAB-LA PrEP. Six macaques infected with SHIV received CAB-LA before seroconversion. We show integrase mutations G118R, E92G/Q, or G140R in plasma from 3/6 macaques as early as day 57, and identify G118R and E92Q in viruses from vaginal and rectal fluids. G118R and G140R confer > 800-fold resistance to CAB and cross-resistance to all licensed integrase inhibitors. Our results emphasize the need for appropriate HIV testing strategies before and possibly shortly after initiating CAB LA PrEP to exclude acute infection.

Long-acting formulation of the integrase inhibitor cabotegravir (CAB LA) is in clinical development for HIV pre-exposure prophylaxis (PrEP). Here, using a SHIV macaque model, the authors show emergence of integrase mutations associated to CAB LA PrEP that confer pan-integrase inhibitor resistance.

Dolutegravir Monotherapy of Simian Immunodeficiency Virus-Infected Macaques Selects for Several Patterns of Resistance Mutations with Variable Virological Outcomes

Drug resistance remains a major concern for human immunodeficiency virus (HIV) treatment. To date, very few resistance mutations have emerged in first-line combination therapy that includes the integrase strand transfer inhibitor (INSTI) dolutegravir (DTG). In vitro, DTG selects for several primary mutations that induce low-level DTG resistance; secondary mutations, while increasing the level of resistance, however, further impair replication fitness, which raised the idea that DTG monotherapy may be feasible. The simian immunodeficiency virus (SIV) rhesus macaque model of HIV infection can be useful to explore this concept. Nine macaques were infected with virulent SIVmac251 and started on DTG monotherapy during either acute (n = 2) or chronic infection (n = 7). Within 4 weeks of treatment, all animals demonstrated a reduction in viremia of 0.8 to 3.5 log RNA copies/ml plasma. Continued treatment led to overall sustained benefits, but the outcome after 10 to 50 weeks of treatment was highly variable and ranged from viral rebound to near pretreatment levels to sustained suppression, with viremia being 0.5 to 5 logs lower than expected based on pretreatment viremia. A variety of mutations previously described to confer low-level resistance of HIV-1 to DTG or other INSTI were detected, and these were sometimes followed by mutations believed to be compensatory. Some mutations, such as G118R, previously shown to severely impair the replication capacity in vitro, were associated with more sustained virological and immunological benefits of continued DTG therapy, while other mutations, such as E92Q and G140A/Q148K, were associated with more variable outcomes. The observed variability of the outcomes in macaques warrants avoidance of DTG monotherapy in HIV-infected people.IMPORTANCE A growing number of anti-HIV drug combinations are effective in suppressing virus replication in HIV-infected persons. However, to reduce their cost and risk for toxicity, there is considerable interest in simplifying drug regimens. A major concern with single-drug regimens is the emergence of drug-resistant viral mutants. It has been speculated that DTG monotherapy may be a feasible option, because DTG may have a higher genetic barrier for the development of drug resistance than other commonly used antiretrovirals. To explore treatment initiation with DTG monotherapy, we started SIV-infected macaques on DTG during either acute or chronic infection. Although DTG initially reduced virus replication, continued treatment led to the emergence of a variety of viral mutations previously described to confer low-level resistance of HIV-1 to DTG, and this was associated with variable clinical outcomes. This unpredictability of mutational pathways and outcomes warns against using DTG monotherapy as initial treatment for HIV-infected people.

Emergence of resistance mutations in simian immunodeficiency virus (SIV)-infected rhesus macaques receiving non-suppressive antiretroviral therapy (ART)

Two SIVmac251-infected rhesus macaques received tenofovir/emtricitabine with raltegravir intensification. Viral rebound occurred during treatment and sequencing of reverse transcriptase and integrase genes identified multiple resistance mutations. Similar to HIV infection, antiretroviral-resistance mutations may occur in SIV-infected nonhuman primates receiving nonsuppressive ART. As ART administration to nonhuman primates is currently dramatically expanding, fueled by both cure research and the study of HIV-related comorbidities, viral resistance should be factored in the study design and data interpretation.

Antiviral Activity of Bictegravir and Cabotegravir against Integrase Inhibitor-Resistant SIVmac239 and HIV-1

Animal models are essential to study novel antiretroviral drugs, resistance-associated mutations (RAMs), and treatment strategies. Bictegravir (BIC) is a novel potent integrase strand transfer inhibitor (INSTI) that has shown promising results against HIV-1 infection in vitro and in vivo and against clinical isolates with resistance against INSTIs. BIC has a higher genetic barrier to the development of resistance than two clinically approved INSTIs, termed raltegravir and elvitegravir. Another clinically approved INSTI, dolutegravir (DTG) also possesses a high genetic barrier to resistance, while a fourth compound, termed cabotegravir (CAB), is currently in late phases of clinical development. Here we report the susceptibilities of simian immunodeficiency virus (SIV) and HIV-1 integrase (IN) mutants containing various RAMs to BIC, CAB, and DTG. BIC potently inhibited SIV and HIV-1 in single cycle infection with 50% effective concentrations (EC₅₀s) in the low nM range. In single cycle SIV infections, none of the E92Q, T97A, Y143R, or N155H substitutions had a significant effect on susceptibility to BIC (≤4-fold increase in EC₅₀), whereas G118R and R263K conferred ∼14-fold and ∼6-fold increases in EC₅₀, respectively. In both single and multiple rounds of HIV-1 infections, BIC remained active against the Y143R, N155H, R263K, R263K/M50I, and R263K/E138K mutants (≤4-fold increase in EC₅₀). In multiple rounds of infection, the G140S/Q148H combination of substitutions decreased HIV-1 susceptibility to BIC 4.8-fold compared to 16.8- and 7.4-fold for CAB and DTG, respectively. BIC possesses an excellent resistance profile in regard to HIV and SIV and could be useful in nonhuman primate models of HIV infection.

Nonhuman Primates and Humanized Mice for Studies of HIV-1 Integrase Inhibitors: A Review

Since the discovery of the first inhibitors of HIV replication, drug resistance has been a major problem in HIV therapy due in part to the high mutation rate of HIV. Therefore, the development of a predictive animal model is important to identify impending resistance mutations and to possibly inform treatment decisions. Significant advances have been made possible through use of nonhuman primates infected by SIV, SHIV, and simian-tropic HIV-1 (stHIV-1), and use of humanized mouse models of HIV-1 infections. In this review, we describe some of the findings from animal models used for the preclinical testing of integrase strand transfer inhibitors. These models have led to important findings about the potential role of integrase strand transfer inhibitors in both the prevention and treatment of HIV-1 infection.