A Yeast-Based Screening System for Differential Identification of Poison Inhibitors and Catalytic Inhibitors of Human Topoisomerase I

Inhibition of human topoisomerase I (TOP1) by camptothecin and topotecan has been shown to reduce excessive transcription of PAMP (Pathogen-Associated Molecular Pattern) -induced genes in prior studies, preventing death from sepsis in animal models of bacterial and SARS-CoV-2 infections. The TOP1 catalytic activity likely resolves the topological constraints on DNA that encodes these genes to facilitate the transcription induction that leads to excess inflammation. The increased accumulation of TOP1 covalent complex (TOP1cc) following DNA cleavage is the basis for the anticancer efficacy of the TOP1 poison inhibitors developed for anticancer treatment. The potential cytotoxicity and mutagenicity of TOP1 targeting cancer drugs pose serious concerns for employing them as therapies in sepsis prevention. The aim of this study is to develop a novel yeast-based screening system that employs yeast strains expressing wild-type or a dominant lethal mutant recombinant human TOP1. This yeast-based screening system can identify human TOP1 poison inhibitors for anticancer efficacy as well as catalytic inhibitors that can inhibit TOP1 DNA binding or cleavage activity in steps prior to the formation of the TOP1cc. In addition to distinguishing between such TOP1 catalytic inhibitors and TOP1 poison inhibitors, results from this yeast-based screening system will also allow elimination of compounds that are likely to be cytotoxic based on their effect on yeast cell growth that is independent of recombinant human TOP1 overexpression.