Biology subjects

Ravichandran, S. M.

Publications and source records attributed to Ravichandran, S. M..

3 recordsLinked to original sources

bioRxiv2026

Unraveling the Mechanism of HIV-1 Hypersusceptibility to Tenofovir Imparted by Islatravir Resistance Mutations

In response to the newly approved antiretroviral therapy (ART) islatravir (ISL), the M184V and A114S resistance mutations have emerged in the human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT). These mutations markedly hypersensitize RT to the globally administered ART tenofovir disoproxil fumarate (TDF). We have solved six structures - four by X-ray crystallography and two by cryo-EM - that capture the single- and double-mutant RTs during inhibitor incorporation and demonstrate the role of the mutations in altering protein-antiviral interactions. These snapshots reveal that the smaller, more flexible TDF diphosphate (TDF-DP) can better accommodate mutation-induced active site changes than ISL triphosphate (ISL-TP). Structural differences between the two inhibitors are consistent with biochemical determination of inhibitory constants (Kis), highlighting differences at the step of inhibitor incorporation. Virological evaluation of ISL and TDF combinations reveals additive inhibition of HIV-1. Given the converse ISL hypersusceptibility imparted by the TDF-resistant K65R mutation, we propose ISL and TDF as a combination that can inspire future therapeutic options.

biochemistry↗

bioRxiv2025

Structural, biophysical, and virological mechanistic characterization of HIV-1 capsid-targeting antivirals

Due to its significant role in virus replication, the HIV capsid is an attractive antiviral target. This is validated by the recent clinical approval of lenacapavir for both treatment and pre-exposure prophylaxis (PrEP). PF74 is a well-characterized capsid-targeting antiviral that was discontinued in further study due to potency and metabolic issues. We hypothesized that making chemical modifications at certain sites of PF74 could result in capsid-targeting antivirals with improved potency and bioavailability. Our cumulative studies show that making changes at the R1 and R3 positions of PF74 results in compounds with increased antiviral potency, increased stability of wild-type HIV capsid hexamers and virions, tighter binding to wild-type HIV capsid hexamer compared to PF74, and different interactions at the "FG" binding site of capsid compared to PF74. These data provide insights into the design of future capsid-targeting antivirals relevant for clinical use.

biochemistry↗

bioRxiv2025

Design, synthesis and profiling of highly potent antivirals targeting emerging drug-resistant HIV-1 variants

AbstractLenacapavir (LEN), the first-in-class HIV capsid inhibitor (CAI), is approved by FDA as a long acting injectable (LAI) for both treatment and pre-exposure prophylaxis (PrEP). Despite its exceptional potency and long pharmacokinetics (PK), a few major resistant mutations have been selected in LEN-treated patients, underscoring the need to develop second-generation LEN analogs to mitigate resistance. Particularly, the M66I mutation confers an extraordinarily high-level LEN resistance, essentially abrogating LEN potency. In this work, we have designed and synthesized LEN analogs featuring a cycloalkyl R2 in subunit B drastically different from known analogs. Against wild-type HIV-1, the potency of our analog 3 (EC50 = 0.073 nM) was 2.6-fold higher than LEN (EC50 = 0.19 nM). More importantly, against the M66I mutant, 3 (EC50 = 5.8 nM) was decisively more potent than LEN (EC50 > 15 M) or any known analogs. We have also shown that the size of the R2 cycloalkyl ring is a major pharmacophore factor as a smaller (cyclopropyl, analog 1) or bigger (cyclohexyl, analog 4) ring confers weaker antiviral potency against both WT HIV-1 and M66I. The vastly improved profile of our lead 3 against M66I was confirmed in the target binding thermal shift assay. These results strongly validate our design and may represent a breakthrough in LEN-based HIV therapy and prophylaxis.

microbiology↗