Dead-end complexes contribute to the synergistic inhibition of HIV-1 RT by the combination of rilpivirine, emtricitabine, and tenofovir

Deciphering the enigmas of non-nucleoside reverse transcriptase inhibitors (NNRTIs): A medicinal chemistry expedition towards combating HIV drug resistance

The pivotal involvement of reverse transcriptase activity in the pathogenesis of the progressive HIV virus has stimulated gradual advancements in drug discovery initiatives spanning three decades. Consequently, nonnucleoside reverse transcriptase inhibitors (NNRTIs) have emerged as a preeminent category of therapeutic agents for HIV management. Academic institutions and pharmaceutical companies have developed numerous NNRTIs, an essential component of antiretroviral therapy. Six NNRTIs have received Food and Drug Administration approval and are widely used in clinical practice, significantly improving the quality of HIV patients. However, the rapid emergence of drug resistance has limited the effectiveness of these medications, underscoring the necessity for perpetual research and development of novel therapeutic alternatives. To supplement the existing literatures on NNRTIs, a comprehensive review has been compiled to synthesize this extensive dataset into a comprehensible format for the medicinal chemistry community. In this review, a thorough investigation and meticulous analysis were conducted on the progressions achieved in NNRTIs within the past 8 years (2016-2023), and the experiences and insights gained in the development of inhibitors with varying chemical structures were also summarized. The provision of a crucial point of reference for the development of wide-ranging anti-HIV medications is anticipated.

Mathematical Modelling of the Molecular Mechanisms of Interaction of Tenofovir with Emtricitabine against HIV

The combination of the two nucleoside reverse transcriptase inhibitors (NRTI) tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) is used in most highly active antiretroviral therapies for treatment of HIV-1 infection, as well as in pre-exposure prophylaxis against HIV acquisition. Administered as prodrugs, these drugs are taken up by HIV-infected target cells, undergo intracellular phosphorylation and compete with natural deoxynucleoside triphosphates (dNTP) for incorporation into nascent viral DNA during reverse transcription. Once incorporated, they halt reverse transcription. In vitro studies have proposed that TDF and FTC act synergistically within an HIV-infected cell. However, it is unclear whether, and which, direct drug–drug interactions mediate the apparent synergy. The goal of this work was to refine a mechanistic model for the molecular mechanism of action (MMOA) of nucleoside analogues in order to analyse whether putative direct interactions may account for the in vitro observed synergistic effects. Our analysis suggests that depletion of dNTP pools can explain apparent synergy between TDF and FTC in HIV-infected cells at clinically relevant concentrations. Dead-end complex (DEC) formation does not seem to significantly contribute to the synergistic effect. However, in the presence of non-nucleoside reverse transcriptase inhibitors (NNRTIs), its role might be more relevant, as previously reported in experimental in vitro studies.

Simulating HIV Breakthrough and Resistance Development During Variable Adherence to Antiretroviral Treatment

BACKGROUND

Barriers to lifelong HIV-1 suppression by antiretrovirals include poor adherence and drug resistance; regimens with higher tolerance to missed doses (forgiveness) would be beneficial to patients. To model short-term nonadherence, in vitro experiments monitoring viral breakthrough (VB) and resistance development were conducted.

METHODS

HIV breakthrough experiments simulated drug exposures at full adherence or suboptimal adherence to bictegravir+emtricitabine+tenofovir alafenamide (BIC+FTC+TAF) or dolutegravir + lamivudine (DTG+3TC). MT-2 cells were infected with wild-type or low frequency M184V HIV-1, exposed to drug combinations, monitored for VB, and rebound virus was deep sequenced. Drug concentrations were determined using human plasma-free adjusted clinical trough concentrations (Cmin), at simulated Cmin after missing 1 to 3 consecutive doses (Cmin - 1 or Cmin - 2, and Cmin - 3) based on drug or active metabolite half-lives.

RESULTS

Cultures infected with wild-type or low frequency M184V HIV-1 showed no VB with BIC+FTC+TAF at drug concentrations corresponding to Cmin, Cmin - 1, or Cmin - 2 but breakthrough did occur in 26 of 36 cultures at Cmin - 3, where the M184V variant emerged in one culture. Experiments using DTG + 3TC prevented most breakthrough at Cmin concentrations (9/60 had breakthrough) but showed more breakthroughs as drug concentrations decreased (up to 36/36) and variants associated with resistance to both drugs emerged in some cases.

CONCLUSIONS

These in vitro VB results suggest that the high potency, long half-lives, and antiviral synergy provided by the BIC/FTC/TAF triple therapy regimen may protect from viral rebound and resistance development after short-term lapses in drug adherence.

Avoiding Drug Resistance in HIV Reverse Transcriptase

HIV reverse transcriptase (RT) is an enzyme that plays a major role in the replication cycle of HIV and has been a key target of anti-HIV drug development efforts. Because of the high genetic diversity of the virus, mutations in RT can impart resistance to various RT inhibitors. As the prevalence of drug resistance mutations is on the rise, it is necessary to design strategies that will lead to drugs less susceptible to resistance. Here we provide an in-depth review of HIV reverse transcriptase, current RT inhibitors, novel RT inhibitors, and mechanisms of drug resistance. We also present novel strategies that can be useful to overcome RT's ability to escape therapies through drug resistance. While resistance may not be completely avoidable, designing drugs based on the strategies and principles discussed in this review could decrease the prevalence of drug resistance.

Combination antiretroviral therapy and cell-cell spread of wild-type and drug-resistant human immunodeficiency virus-1

Human immunodeficiency virus-1 (HIV-1) disseminates between T cells either by cell-free infection or by highly efficient direct cell–cell spread. The high local multiplicity that characterizes cell–cell infection causes variability in the effectiveness of antiretroviral drugs applied as single agents. Whereas protease inhibitors (PIs) are effective inhibitors of HIV-1 cell–cell and cell-free infection, some reverse transcriptase inhibitors (RTIs) show reduced potency; however, antiretrovirals are not administered as single agents and are used clinically as combination antiretroviral therapy (cART). Here we explored the efficacy of PI- and RTI-based cART against cell–cell spread of wild-type and drug-resistant HIV-1 strains. Using a quantitative assay to measure cell–cell spread of HIV-1 between T cells, we evaluated the efficacy of different clinically relevant drug combinations. We show that combining PIs and RTIs improves the potency of inhibition of HIV-1 and effectively blocks both cell-free and cell–cell spread. Combining drugs that alone are poor inhibitors of cell–cell spread markedly improves HIV-1 inhibition, demonstrating that clinically relevant combinations of ART can inhibit this mode of HIV-1 spread. Furthermore, comparison of wild-type and drug-resistant viruses reveals that PI- and RTI-resistant viruses have a replicative advantage over wild-type virus when spreading by cell–cell means in the presence of cART, suggesting that in the context of inadequate drug combinations or drug resistance, cell–cell spread could potentially allow for ongoing viral replication.

Emtricitabine/rilpivirine/tenofovir disoproxil fumarate single-tablet regimen: a review of its use in HIV infection

The nucleos(t)ide reverse transcriptase inhibitors, emtricitabine and tenofovir disoproxil fumarate (tenofovir DF), and the non-nucleoside reverse transcriptase inhibitor, rilpivirine, are now available as a fixed-dose single-tablet regimen (emtricitabine/rilpivirine/tenofovir DF; Complera(®), Eviplera(®)) for the treatment of adults infected with HIV-1. In treatment-naïve adults, once-daily emtricitabine/rilpivirine/tenofovir DF was noninferior to once-daily emtricitabine/efavirenz/tenofovir DF with regard to establishing virological suppression over 96 weeks of therapy in a randomized, open-label, phase IIIb study (STaR). These data confirmed the findings of a pooled subset analysis of two earlier 96-week, double-blind, phase III trials (ECHO and THRIVE) in which treatment-naïve adults received either rilpivirine or efavirenz in combination with emtricitabine/tenofovir DF. However, the virological benefit of emtricitabine/rilpivirine/tenofovir DF in this setting appeared limited in patients with low CD4+ cell counts or high viral loads at baseline. In 48-week phase IIIb (SPIRIT) and IIb (Study 111) trials in treatment-experienced patients already virologically suppressed with a single- or multiple-tablet antiretroviral regimen and without prior virological failure, switching to once-daily emtricitabine/rilpivirine/tenofovir DF maintained virological suppression and was noninferior to remaining on a more complex multiple-tablet regimen in this regard. Emtricitabine/rilpivirine/tenofovir DF is generally well tolerated and appears to have a more favourable tolerability profile than emtricitabine/efavirenz/tenofovir DF. Thus, emtricitabine/rilpivirine/tenofovir DF is a welcome addition to the other single-tablet regimens currently available for the treatment of HIV-1 infection, providing a convenient and effective option for some adults who are treatment-naïve, as well as those who are already virologically suppressed on their current treatment regimen and wish to switch because of intolerance or to simplify their regimen.

The combined anti-HIV-1 activities of emtricitabine and tenofovir plus the integrase inhibitor elvitegravir or raltegravir show high levels of synergy in vitro

Highly active antiretroviral therapy (HAART) involves combination treatment with three or more antiretroviral agents. The antiviral effects of combinations of emtricitabine (FTC) plus tenofovir (TFV) plus antiretroviral agents of all the major drug classes were investigated. Combinations of FTC and TFV with a nonnucleoside reverse transcriptase inhibitor (NNRTI) (efavirenz or rilpivirine) or with a protease inhibitor (PI) (atazanavir, lopinavir, or darunavir) showed additive to synergistic anti-HIV-1 activity. FTC-TFV with an HIV-1 integrase strand transfer inhibitor (INSTI) (elvitegravir or raltegravir) showed the strongest synergy. Anti-HIV-1 synergy suggests enhancement of individual anti-HIV-1 activities within cells that may contribute to potent treatment efficacy and open new areas of research into interactions between reverse transcriptase (RT) and integrase inhibitors.