Structural and Biochemical Effects of Capsid-targeting Molecules on HIV-1 Capsid Assembly

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Abstract HIV infection impacts over 37 million individuals, with over 2/3 of these patients receiving antiretroviral therapies (ART). ART is sustained for a patient’s life and can lead to the emergence of drug-resistant HIV-1. To combat drug-resistance, an improved and diverse set of antiretrovirals are needed for clinical use. To this extent, the HIV-1 capsid is an excellent target for antiretroviral therapies as it has numerous, essential roles throughout the HIV-1 replication cycle. Compounds that target the capsid protein (CA), known as capsid effectors (CEs), offer a novel class of HIV-1 antivirals for potential clinical use. One CE with marked success is lenacapavir, developed by Gilead Sciences. Lenacapavir is exceptionally potent, however, early results show treatment with lenacapavir can cause the emergence of antiviral-resistant HIV-1. Our lab has previously reported highly potent antiretrovirals that target the same site as lenacapavir, within the FG-binding pocket. Compounds that bind to the FG-binding pocket of CA mimic a conserved phenylalanine-glycine (FG) dipeptide motif found in many host factors reported to bind CA. Here, I will characterize structural changes to the HIV-1 capsid upon treatment with highly potent CEs that bind the FG-binding pocket and calculate the biochemical parameters of CA•CE interactions for this class of antiretroviral therapeutics. The nature of CA•CE interactions will be assessed in wild-type (WT) and drug-resistant viruses to further our understanding of antiviral resistance. Electron microscopy (EM) will be used to visualize drug-resistant capsid assemblies and discern structural changes relative to WT assemblies (AIM 1). Rates of capsid assembly and changes to thermal stability upon drug-treatment will be calculated using assays designed to probe CA•CA interactions (AIM 2). These aims will study mutations that confer antiviral-resistance and results will be compared to WT CA to identify those with similar phenotypes and therefore higher risks of resistance. Further, CA•CE biochemical parameters of affinity and dissociation rates will be solved by label-free optical detection. This study will further our mechanistic understanding of compounds that bind to the FG-binding pocket of CA. Overall, these results will enable future research to strategically improve antiretrovirals, aiming to combat the HIV-1 epidemic.