A potent and selective reaction hijacking inhibitor ofPlasmodium falciparumtyrosine tRNA synthetase exhibits single dose oral efficacyin vivo

Abstract

AbstractThePlasmodium falciparumcytoplasmic tyrosine tRNA synthetase (PfTyrRS) is an attractive drug target that is susceptible to reaction-hijacking by AMP-mimicking nucleoside sulfamates. We previously identified an exemplar pyrazolopyrimidine ribose sulfamate, ML901, as a potent pro-inhibitor ofPfTyrRS. Here we examined the stage specificity of action of ML901, showing very good activity against the schizont stage, but lower trophozoite stage activity. We explored a series of ML901 analogues and identified ML471, which exhibits improved potency against trophozoites and enhanced selectivity against a human cell line. Additionally, it has no inhibitory activity against human ubiquitin-activating enzyme (UAE)in vitro. ML471 exhibits low nanomolar activity against asexual blood stageP. falciparumand potent activity against liver stage parasites, gametocytes and transmissible gametes. It is fast-acting and exhibits a longin vivohalf-life. ML471 is well-tolerated and shows single dose oral efficacy in the SCID mouse model ofP. falciparummalaria. We confirm that ML471 is a pro-inhibitor that is converted into a tight binding Tyr-ML471 conjugate by thePfTyrRS enzyme. A crystal structure of thePfTyrRS/ Tyr-ML471 complex offers insights into improved potency, while molecular docking into UAE provides a rationale for improved selectivity.