Efficacy and mechanism of action of cipargamin as an antibabesial drug candidate.

Abstract

Babesiosis is a disease brought on by intraerythrocytic parasites of the genus <i>Babesia</i>. Current chemotherapies are accompanied by side effects and parasite relapse. Therefore, it is crucial to develop highly effective drugs against <i>Babesia</i>. Cipargamin (CIP) has shown inhibition against apicomplexan parasites, mainly <i>Plasmodium</i> and <i>Toxoplasma</i>. This study evaluated the growth-inhibiting properties of CIP against <i>Babesia</i> spp. and investigated the mechanism of CIP on <i>B. gibsoni</i>. The half inhibitory concentration (IC₅₀) values of CIP against the in vitro growth of <i>B. bovis</i> and <i>B. gibsoni</i> were 20.2 ± 1.4 and 69.4 ± 2.2 nM, respectively. CIP significantly inhibited the growth of <i>B. microti</i> and <i>B. rodhaini</i> in vivo. Resistance was conferred by L921V and L921I mutations in BgATP4, which reduced the sensitivity to CIP by 6.1- and 12.8-fold. The inhibitory potency of CIP against BgATP4-associated ATPase activity was moderately reduced in mutant strains, with a 1.3- and 2.4-fold decrease in BgATP4^L921V and BgATP4^L921I, respectively, compared to that of BgATP4^WT. An in silico investigation revealed reductions in affinity for CIP binding to BgATP4^L921V and BgATP4^L921I compared to BgATP4^WT. Resistant strains showed no significant cross-resistance to atovaquone or tafenoquine succinate (TQ), with less than a onefold change in IC₅₀ values. Combining CIP with TQ effectively eliminated <i>B. microti</i> infection in SCID mice with no relapse, and parasite DNA was not detected by qPCR within 90 days post-infection. Our findings reveal the efficacy of CIP as an antibabesial agent, its limitations as a monotherapy due to resistance development, and the potential of combination therapy with TQ to overcome said resistance and achieve complete parasite clearance.