Cryptosporidium and Toxoplasma Parasites Are Inhibited by a Benzoxaborole Targeting Leucyl-tRNA Synthetase

Abstract

ABSTRACTThe apicomplexan parasitesCryptosporidiumandToxoplasmaare serious threats to human health. Cryptosporidiosis is a severe diarrheal disease in malnourished children and immunocompromised individuals, with the only FDA-approved drug treatment currently being nitazoxanide. The existing therapies for toxoplasmosis, an important pathology in immunocompromised individuals and pregnant women, also have serious limitations. With the aim of developing alternative therapeutic options to address these health problems, we tested a number of benzoxaboroles, boron-containing compounds shown to be active against various infectious agents, for inhibition of the growth ofCryptosporidiumparasites in mammalian cells. A 3-aminomethyl benzoxaborole, AN6426, with activity in the micromolar range and with activity comparable to that of nitazoxanide, was identified and further characterized using biophysical measurements of affinity and crystal structures of complexes with the editing domain ofCryptosporidiumleucyl-tRNA synthetase (LeuRS). The same compound was shown to be active againstToxoplasmaparasites, with the activity being enhanced in the presence of norvaline, an amino acid that can be mischarged by LeuRS. Our observations are consistent with AN6426 inhibiting protein synthesis in bothCryptosporidiumandToxoplasmaby forming a covalent adduct with tRNALeuin the LeuRS editing active site and suggest that further exploitation of the benzoxaborole scaffold is a valid strategy to develop novel, much needed antiparasitic agents.