Inhibitory effect of naphthoquine phosphate on Babesia gibsoni in vitro and Babesia rodhaini in vivo

Anti-babesial activity of a series of 6,7-dimethoxyquinazoline-2,4-diamines (DMQDAs)

Diminazene aceturate (DA), imidocarb dipropionate (ID), atovaquone (ATO), azithromycin (AZI), clindamycin, and quinine have been used to treat animal and human babesiosis for many years, despite their negative effects and rising indications of resistance. Thus, finding anti-babesial compounds that can either treat the infection or lower the dose of drugs given has been a primary objective. Quinazolines are one of the most important nitrogen heterocycles, with a wide range of pharmacological activities including analgesic, anti-inflammatory, sedative-hypnotic, anti-histaminic, anti-cancer, and anti-protozoan properties. The present study investigated the anti-babesial activities of twenty 6,7-dimethoxyquinazoline-2,4-diamines on Babesia spp. One candidate, 6,7-dimethoxy-N4-ethylisopropyl-N2-ethyl(pyridin-4-yl)quinazoline-2,4-diamine (SHG02), showed potent inhibition on Babesia gibsoni in vitro, as well as on B. microti and B. rodhaini in mice. Our findings indicate that the candidate compound SHG02 is promising for further development of anti-babesial drugs and provides a new structure to be explored for developing anti-Babesia therapeutics.

Efficacy of the Antimalarial MMV390048 against Babesia Infection Reveals Phosphatidylinositol 4-Kinase as a Druggable Target for Babesiosis

The present study aimed to evaluate the anti-Babesia effect of MMV390048, a drug that inhibits Plasmodium by targeting the phosphatidylinositol 4-kinase (PI4K). The half inhibitory concentration (IC₅₀) of MMV390048 against the in vitro growth of Babesia gibsoni was 6.9 ± 0.9 μM. In immunocompetent mice, oral treatment with MMV390048 at a concentration of 20 mg/kg effectively inhibited the growth of B. microti (Peabody mjr strain). The peak parasitemia in the control group was 30.5%, whereas the peak parasitemia in the MMV390048-treated group was 3.4%. Meanwhile, MMV390048 also showed inhibition on the growth of B. rodhaini (Australia strain), a highly pathogenic rodent Babesia species. All MMV390048-treated mice survived, whereas the mice in control group died within 10 days postinfection (DPI). The first 7-day administration of MMV390048 in B. microti-infected, severe combined immunodeficiency (SCID) mice delayed the rise of parasitemia by 26 days. Subsequently, a second 7-day administration was given upon recurrence. At 52 DPI, a parasite relapse (in 1 out of 5 mice) and a mutation in the B. microti PI4K L746S, a MMV390048 resistance-related gene, were detected. Although the radical cure of B. microti infection in immunocompromised host SCID mice was not achieved, results from this study showed that MMV390048 has excellent inhibitory effects on Babesia parasites, revealing a new treatment strategy for babesiosis: targeting the B. microti PI4K.