Discovering Thiamine Transporters as Targets of Chloroquine Using a Novel Functional Genomics Strategy

Chloroquine (cq) and other quinoline-containing antimalarials are important drugs with many therapeutic benefits as well as adverse effects. however,the molecular targets underlying most such effects are largely unknown. by taking a novel functional genomics strategy,which employs a unique combination of genome-wide drug-gene synthetic lethality (dgsl),gene-gene synthetic lethality (ggsl),and dosage suppression (ds) screens in the model organism saccharomyces cerevisiae and is thus termed sl/ds for simplicity,we found that cq inhibits the thiamine transporters thi7,nrt1,and thi72 in yeast. we first discovered a thi3δ mutant as hypersensitive to cq using a genome-wide dgsl analysis. using genome-wide ggsl and ds screens,we then found that a thi7δ mutation confers severe growth defect in the thi3δ mutant and that thi7 overexpression suppresses cq-hypersensitivity of this mutant. we subsequently showed that cq inhibits the functions of thi7 and its homologues nrt1 and thi72. in particular,the transporter activity of wild-type thi7 but not a cq-resistant mutant (thi7t287n) was completely inhibited by the drug. similar effects were also observed with other quinoline-containing antimalarials. in addition,cq completely inhibited a human thiamine transporter (slc19a3) expressed in yeast and significantly inhibited thiamine uptake in cultured human cell lines. therefore,inhibition of thiamine uptake is a conserved mechanism of action of cq. this study also demonstrated sl/ds as a uniquely effective methodology for discovering drug targets. © 2012 huang et al.