gp41 sequence variability in HIV type 1 non-B subtypes infected patients undergoing enfuvirtide pressure

Massively Parallel Profiling of HIV-1 Resistance to the Fusion Inhibitor Enfuvirtide

Identifying drug resistance mutations is important for the clinical use of antivirals and can help define both a drug’s mechanism of action and the mechanistic basis of resistance. Resistance mutations are often identified one-at-a-time by studying viral evolution within treated patients or during viral growth in the presence of a drug in cell culture. Such approaches have previously mapped resistance to enfuvirtide, the only clinically approved HIV-1 fusion inhibitor, to enfuvirtide’s binding site in the N-terminal heptad repeat (NHR) of the Envelope (Env) transmembrane domain as well as a limited number of allosteric sites. Here, we sought to better delineate the genotypic determinants of resistance throughout Env. We used deep mutational scanning to quantify the effect of all single-amino-acid mutations to the subtype A BG505 Env on resistance to enfuvirtide. We identified both previously characterized and numerous novel resistance mutations in the NHR. Additional resistance mutations clustered in other regions of Env conformational intermediates, suggesting they may act during different fusion steps by altering fusion kinetics and/or exposure of the enfuvirtide binding site. This complete map of resistance sheds light on the diverse mechanisms of enfuvirtide resistance and highlights the utility of using deep mutational scanning to comprehensively map potential drug resistance mutations.

Polymorphisms in the HIV-1 gp41 env gene, natural resistance to enfuvirtide (T-20) and pol resistance among pregnant Brazilian women

The selective pressure of antiretroviral drugs (ARVs) targeting HIV-1 pol can promote drug resistance mutations in other genomic regions, such as env. Drug resistance among women should be monitored to avoid horizontal and mother-to-child transmission. To describe natural resistance to T-20 (enfuvirtide), gp41 env polymorphisms, mutations in pol and HIV-1 subtypes, 124 pregnant women were recruited. For 98 patients, the gp41 env, protease (PR) and reverse transcriptase (RT) fragments were sequenced. The patients were ARV naïve (n = 30), taking mother-to-child transmission prophylaxis (n = 50), or being treated with highly active ARV therapy/HAART (n = 18). The Stanford and IAS/USA databases and other sources were used to analyze PR/RT, gp41 env resistance mutations. The HIV-1 genetic diversity was analyzed by REGA/phylogenetic analyses. The patients' median age was 25 years (range, 16-42), 18.4% had AIDS. The frequency of natural resistance to T-20 (N42D, L44M, and R46M-low-impact mutations) was 6.1% (6/98); 20.4% (20/98) had compensatory mutations in HR2. The prevalence of transmitted drug resistance in the pol was 13.3% (4/30), and the prevalence of secondary drug resistance was 33.3% (6/18). Two patients were infected with multidrug resistant/MDR viruses. The analysis of HIV-1 subtypes (PR/RT/gp41) revealed that 61.2% (60/98) were subtype B, 12.2% (12/98) were subtype C, 4.1% (4/98) were subtype F1, and 22.4% (22/98) were possible recombinants (BF1 = 20.4%; BC = 2%). Natural resistance to T-20 was not associated with pol resistance or previous ARV use. The high rate of secondary resistance, including MDR, indicates that the number of women that may need T-20 salvage therapy may be higher than anticipated.

Genotypic analysis of the gp41 HR1 region from HIV-1 isolates from enfuvirtide-treated and untreated patients

OBJECTIVE

To evaluate the polymorphisms and resistance mutations in gp41 HR1 region of HIV-1.

METHODS

The study included 28 HIV-positive patients undergoing enfuvirtide (ENF) treatment or not from Porto Alegre, Rio Grande do Sul state, and Rio de Janeiro, Rio de Janeiro state, between 2006 and 2009. Resistance mutations and polymorphisms of the gp41 HR1 region were detected using the genomic DNA of 12 ENF-untreated patients and 16 patients in ENF treatment, encompassing subtypes B, C, and F1. Sample subtypes were determined by neighbor-joining phylogenetic analysis with a Kimura's two-parameter correction.

RESULTS

A high prevalence of polymorphisms unrelated to resistance was observed. Among ENF-untreated patients, 16% showed mutations related with resistance. Among patients in ENF treatment, 50% had resistance-related mutations. Overall, 17% of all isolates showed the N42S polymorphism related to ENF hypersusceptibility. The presence of ENF resistance mutations in the group of treated patients reduced viral load. The V38A substitution was the most frequent among treatment-experienced patients followed by the G36D/E, N42D, and V38M substitutions.

CONCLUSIONS

The V38A substitution in the gp41 HR region was the most common resistance mutation among ENF-treated patients and was associated with increased viral load.

Clinical management of HIV drug resistance

Combination antiretroviral therapy for HIV-1 infection has resulted in profound reductions in viremia and is associated with marked improvements in morbidity and mortality. Therapy is not curative, however, and prolonged therapy is complicated by drug toxicity and the emergence of drug resistance. Management of clinical drug resistance requires in depth evaluation, and includes extensive history, physical examination and laboratory studies. Appropriate use of resistance testing provides valuable information useful in constructing regimens for treatment-experienced individuals with viremia during therapy. This review outlines the emergence of drug resistance in vivo, and describes clinical evaluation and therapeutic options of the individual with rebound viremia during therapy.

Enfuvirtide antiretroviral therapy in HIV-1 infection

It has been over 25 years since the first diagnosis of what would be known as AIDS. Although great strides in anti-HIV therapeutics have been made, there is still a great need for antiretrovirals that are effective against drug-resistant HIV. Enfuvirtide (ENF) is the first of a new class of fusion inhibitors to be approved by the US Food and Drug Administration for use in combination with other antiretroviral agents among HIV-1 infected patients with previous treatment experience. The inclusion of enfuvirtide in an optimized antiretroviral background regimen for the treatment of HIV-1 infected (treatment-experienced) patients followed the success of two critical clinical trials (TORO: T20 vs Optimized Regimen Only I and II). Even though injection-site reactions persisted in these trials, improved virological and immunological responses were observed among patients. Challenges associated with ENF treatment include the high cost of the drug, injection-site reactions, determining the optimal time to initiate treatment, and the potential for the selection of drug resistant mutants and viral evolution. ENF is a promising novel treatment for HIV infected individuals whose choices for effective treatment are limited by previous treatment and resistance. Understanding the implications of viral fitness and evolution in the presence of ENF treatment is crucial in determining effective and safe treatment regimens, particularly among treatment-experienced patients.