Evaluation of the sigma-1 receptor as a potential therapeutic target for COVID-19

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Aim 1. Classify antagonists and agonists by ligand-induced 1R oligomerization For several 1R antagonists that have been shown to reduce SARS-CoV-2 infectivity, the original studies in determining their 1R antagonist properties are either vague or do not exist (e.g., those for PB28), not mentioning at in vitro level using 1R specific functional assays as we have developed. Thus, we will use BRET, binding, and western blot assays specifically developed for 1R in my lab, to evaluate whether the ligands that have been found to have either anti-viral or pro-viral activities indeed have opposite functions at 1R, and to assess whether 1R is a valid therapeutic target for COVID-19. If 1R will be found to be an effective therapeutic target for COVID-19 either by us or by other groups, we will seek to develop a BRET assay to characterize ligand-induced effects on the 1R-Nsp6 interaction, similar to our previous characterizations of the protein-protein interactions between 1R and its client proteins. Such an assay will serve to further evaluate the feasibility of targeting the 1R-Nsp6 interface for the therapeutic purposes and to validate the hit compounds from our own virtual screening (see below). Aim 2. Discover and develop the ligands for 1R and against hERG Several 1R antagonists were found to have significant affinities at hERG, which may result in cardiotoxicity when used at high doses. As 1R can be potential drug targets for the treatment of cocaine abuse and COVID-19, we will identify and develop novel high-affinity 1R antagonists that possess low affinity at hERG. Specifically, we will adapt the existing platform that integrated chemoinformatics, molecular modeling, and in vitro assays to i) screen novel 1R ligands that do not possess significant affinity at hERG; and ii) to rationally optimize current scaffolds of the 1R ligands that show promising therapeutic effects. To further enhance the integration, we will use molecular modeling and simulations and network analysis of 1R to investigate the specific binding modes of selected ligands that may induce receptor conformational changes to affect 1R homomerization state. Thus, by in silico characterizations of these changes, we will connect the conformational changes of the 1R (and/or its client proteins) to pharmacological readouts from the BRET and western blot assays we have developed.