Anti-malarial benzoxaboroles target P. falciparum leucyl-tRNA synthetaseEbere Sonoiki, Andres Palencia, Denghui Guo, Vida Ahyong, Chen Dong, Xianfeng Li, Vincent S. Hernandez, Yong-Kang Zhang, Wai Choi, Jiri Gut, Jenny Legac, Roland Cooper, M.R.K Alley, Yvonne R. Freund, Joseph DeRisi, Stephen Cusack, Philip J. Rosenthal
AAC, 2016Abstract: There is a need for new antimalarials, ideally with novel mechanisms of action. Benzoxaboroles have been shown to be active against bacteria, fungi, and trypanosomes. Therefore, we investigated the antimalarial activity and mechanism of action of 3-aminomethyl benzoxaboroles against Plasmodium falciparum. Two 3-aminomethyl compounds, AN6426 and AN8432, demonstrated good potency against cultured multidrug-resistant (W2 strain) P. falciparum (IC50 310 nM and 490 nM, respectively) and efficacy against murine Plasmodium berghei infection when administered orally once daily for 4 days (ED90 7.4 and 16.2 mg/kg, respectively). To characterize mechanisms of action, we selected parasites with decreased drug sensitivity by culturing with step-wise increases in concentration of AN6426. Resistant clones were characterized by whole genome sequencing. Three generations of resistant parasites had polymorphisms in the predicted editing domain of the gene encoding a P. falciparum leucyl-tRNA synthetase (LeuRS; PF3D7_0622800) and in another gene (PF3D7_1218100), which encodes a protein of unknown function. Solution of the structure of the P. falciparum LeuRS editing domain suggested key roles for mutated residues in LeuRS editing. Short incubations with AN6426 and AN8432, unlike artemisinin, caused dose-dependent inhibition of [14C]leucine incorporation by cultured wild type, but not resistant parasites. The growth of resistant, but not wild type parasites was impaired in the presence of the unnatural amino acid norvaline, consistent with a loss of LeuRS editing activity in resistant parasites. In summary, the benzoxaboroles AN6426 and AN8432 offer effective antimalarial activity, and act, at least in part, against a novel target, the editing domain of P. falciparum LeuRS.
