Single Oral Doses of MK-8507, a Novel Non-Nucleoside Reverse Transcriptase Inhibitor, Suppress HIV-1 RNA for a Week

The Current Pipeline of Antiretroviral Therapy: Expanding Options and Filling Gaps

Highly effective antiretroviral therapy (ART) has transformed human immunodeficiency virus (HIV) care in the past 3 decades. 30 years ago, how many would have imagined that a single-tablet daily ART regimen containing different drug classes could achieve sustained HIV-1 suppression and halt disease progression to acquired immunodeficiency syndrome (AIDS)? Despite this remarkable achievement, challenges in HIV care remain that require further innovation for ART. In this review, we focus on newly approved antiretroviral agents and those undergoing phase 2/3 clinical trials. These new antiretrovirals hold great promise to expand treatment options and fill gaps in HIV care.

The predictive value of macaque models of preexposure prophylaxis for HIV prevention

PURPOSE OF REVIEW

We review macaque models for preexposure prophylaxis (PrEP) for HIV prevention and highlight their role in advancing currently approved and novel PrEP agents.

RECENT FINDINGS

The development of the repeat low dose simian HIV (SHIV) challenge models represented a significant advancement in preclinical PrEP modeling that has allowed the investigation of PrEP under conditions that better mimic HIV exposures in humans. These models incorporate relevant drug pharmacology to inform drug correlates of PrEP protection. Models of rectal, vaginal, and penile infection are now available and have been found to predict clinical efficacy of all the currently approved PrEP strategies including daily oral PrEP with the combination of emtricitabine and tenofovir disoproxil fumarate or tenofovir alafenamide, and a long-acting formulation of the integrase inhibitor cabotegravir. These models are being used to test new PrEP modalities including the nucleoside reverse transcriptase-translocation inhibitor islatravir and long-acting capsid inhibitors. The SHIV models have also been supplemented by sexually transmitted infection co-infections with Chlamydia trachomatis, Treponema pallidum or Trichomonas vaginalis to assess the impact of inflammation on PrEP efficacy.

SUMMARY

Clinical efficacy validated current PrEP macaque models supporting their continued use to advance novel PrEP agents to improve global PrEP coverage.

Islatravir Has a High Barrier to Resistance and Exhibits a Differentiated Resistance Profile from Approved Nucleoside Reverse Transcriptase Inhibitors (NRTIs)

Islatravir (ISL) is a nucleoside reverse transcriptase translocation inhibitor (NRTTI) that inhibits human immunodeficiency virus (HIV) reverse transcription by blocking reverse transcriptase (RT) translocation on the primer:template. ISL is being developed for the treatment of HIV-1 infection. To expand our knowledge of viral variants that may confer reduced susceptibility to ISL, resistance selection studies were conducted with wild-type (WT) subtype A, B, and C viruses. RT mutations encoding M184I and M184V were the most frequently observed changes. Selection studies were also initiated with virus containing a single known resistance-associated mutation in RT (K65R, L74I, V90I, M184I, or M184V), and no additional mutations were observed. Antiviral activity assays were performed on variants that emerged in selection studies to determine their impact. M184I and M184V were the only single-codon substitutions that reduced susceptibility >2-fold compared to WT. A114S was an emergent substitution that when combined with other substitutions further reduced susceptibility >2-fold. Viruses containing A114S in combination with M184V did not replicate in primary blood mononuclear cells (PBMCs), consistent with the rare occurrence of the combination in clinical samples. While A114S conferred reduced susceptibility to ISL, it increased susceptibility to approved nucleoside reverse transcriptase inhibitors (NRTIs). This differential impact of A114S on ISL, an NRTTI, compared to NRTIs likely results from the different mechanisms of action. Altogether, the results demonstrate that ISL has a high barrier to resistance and a differentiated mechanism compared to approved NRTIs.

Approved HIV reverse transcriptase inhibitors in the past decade

HIV reverse transcriptase (RT) inhibitors are the important components of highly active antiretroviral therapies (HAARTs) for anti-HIV treatment and pre-exposure prophylaxis in clinical practice. Many RT inhibitors and their combination regimens have been approved in the past ten years, but a review on their drug discovery, pharmacology, and clinical efficacy is lacking. Here, we provide a comprehensive review of RT inhibitors (tenofovir alafenamide, rilpivirine, doravirine, dapivirine, azvudine and elsulfavirine) approved in the past decade, regarding their drug discovery, pharmacology, and clinical efficacy in randomized controlled trials. Novel RT inhibitors such as islatravir, MK-8504, MK-8507, MK8583, IQP-0528, and MIV-150 will be also highlighted. Future development may focus on the new generation of novel antiretroviral inhibitors with higher bioavailability, longer elimination half-life, more favorable side-effect profiles, fewer drug-drug interactions, and higher activities against circulating drug-resistant strains.