Mechanisms of HIV-1 Hypersensitivity to Islatravir

PROJECT SUMMARY/ ABSTRACT As of 2020, 37.7 million patients are living with human immunodeficiency virus type 1 (HIV-1). Combination antiretroviral therapies (cARTs) are used to treat HIV-1 infected patients, but the effectiveness of these cARTs is threatened by viral drug resistance mutations most frequently caused by patient non-adherence to daily dosing regimens. Potent antivirals with long-acting potential are urgently needed to prevent drug resistance mutations. Islatravir (4’-ethynyl-2-fluoro-2’-deoxyadenosine), often referred to as EFdA, is a highly potent long-acting HIV- 1 nucleoside reverse transcriptase (RT) translocation inhibitor currently in phase III clinical trials. In these clinical trials, EFdA is administered in combination with other HIV-1 antivirals including non-nucleoside RT inhibitors. Interestingly, non-nucleoside RT inhibitor (NNRTI) treatment, which include Doravirine, Etravirine, Rilpivirine, or Elsulfavirine, leads to the RT F227C mutation, which remarkably makes HIV-1 more susceptible to EFdA. However, why a mutation located at the distant non-nucleoside RT inhibitor pocket would cause RT to become hypersensitive to EFdA, a compound that binds at the polymerase active site is not understood. Studies are needed to understand the mechanism of RTF227C hypersensitivity to EFdA and how this mutation affects HIV-1 susceptibility to various RT antivirals. I hypothesize that the F227C mutation at the NNRTI binding pocket structurally alters the polymerase active site, causing hypersensitivity to EFdA. To test this hypothesis, I will first determine the structural basis of RTF227C hypersensitivity to EFdA using X-ray crystallography (Aim 1). Second, I will determine the biochemical basis of RTF227C hypersensitivity to EFdA through a battery of biochemical assays. These assays will test how the F227C mutation impacts EFdA-triphosphate incorporation, the ability of RT to unblock EFdA-terminated primers, and the ability of RT to translocate along the nucleic acid (Aim 2). Finally, I will determine how the F227C mutation affects HIV-1 susceptibility to various EFdA and RT inhibitor combinations through biochemical and cell-based assays (Aim 3). I will take full advantage of our lab’s background in RT biology and role in the development of EFdA, as it provides the necessary environment, equipment, and streamlined protocols to complete these proposed experiments and contribute to my training. These planned studies will not only advance the understanding of how RT drug resistance mutations impart hypersensitivity to EFdA but will also aid in the development of optimized combinations with EFdA for the treatment of HIV-1.