Novel arylimidamides for treatment of visceral leishmaniasis

Abstract

Arylimidamides (AIAs) represent a new class of molecules that exhibit potent antileishmanial activity (50% inhibitory concentration [IC(50)], <1 microM) against both Leishmania donovani axenic amastigotes and intracellular Leishmania, the causative agent for human visceral leishmaniasis (VL). A systematic lead discovery program was employed to characterize in vitro and in vivo antileishmanial activities, pharmacokinetics, mutagenicities, and toxicities of two novel AIAs, DB745 and DB766. They were exceptionally active (IC(50) < or = 0.12 microM) against intracellular L. donovani, Leishmania amazonensis, and Leishmania major and did not exhibit mutagenicity in an Ames screen. DB745 and DB766, given orally, produced a dose-dependent inhibition of liver parasitemia in two efficacy models, L. donovani-infected mice and hamsters. Most notably, DB766 (100 mg/kg of body weight/day for 5 days) reduced liver parasitemia in mice and hamsters by 71% and 89%, respectively. Marked reduction of parasitemia in the spleen (79%) and bone marrow (92%) of hamsters was also observed. Furthermore, these compounds distributed to target tissues (liver and spleen) and had a moderate oral bioavailability (up to 25%), a large volume of distribution, and an elimination half-life ranging from 1 to 2 days in mice. In a repeat-dose toxicity study of mice, there was no indication of liver or kidney toxicity for DB766 from serum chemistries, although mild hepatic cell eosinophilia, hypertrophy, and fatty changes were noted. These results demonstrated that arylimidamides are a promising class of molecules that possess good antileishmanial activity and desirable pharmacokinetics and should be considered for further preclinical development as an oral treatment for VL.

FIG. 1.

Chemical structures of two novel AIAs, DB745 and DB766.

FIG. 2.

In vivo efficacy levels of DB745 and DB766 in the murine VL model. Compounds were given i.p. (A and C) or p.o. (B and D) once daily for 5 days to mice infected with L. donovani promastigotes. Results are presented as the percentage of reduction in liver parasitemia (LDU) versus untreated controls. Miltefosine given i.p. served as a positive control in all groups. Bars and error bars denote the means and standard deviations, respectively, of experimental groups containing four animals. *, P < 0.05, compared to untreated control; #, mice in this group received only four doses due to toxicity.

FIG. 3.

DB766 tissue concentrations in mice after a single i.v. (A) or p.o. (B) administration of DB766. Plasma concentrations were plotted for the purpose of comparison. Tissue concentrations were calculated assuming that 1 g of wet tissue equals 1 ml in volume. Symbols and error bars denote the means and standard errors, respectively, of triplicate determinations.