The unique bisubunit structure of Leishmania
donovani topoisomerase 1B (LdTop1) is a potential drug target
in the parasites
unlike the monomeric Top1 from its human host counterpart. Here, we
report the design, synthesis, and validation of a chimeric pyrido[2′,1′:2,3]imidazo[4,5-c]quinoline derivative (C17) as a novel antileishmanial
agent that poisons topoisomerase 1-DNA covalent complexes (LdTop1cc)
inside the parasites and inhibits Top1 religation activity both in
the drug sensitive and antimony-resistant L. donovani clinical isolates. Importantly, the human Top1 is not sensitive
to C17. Further, C17 overcomes the chemical
instability of camptothecin (CPT) by generating persistent LdTop1cc-induced
DNA breaks inside the parasites even after 12 h of drug removal. Intraperitoneal
administration of C17 results in marked reduction of
the Leishmania amastigotes from the infected spleen
and liver of BALB/c mice. C17 confers a host protective
immune-response up-regulating the Th1 cytokines facilitating parasite
clearance which can be exploited for treating drug-resistant leishmaniasis.