Identification, Optimization, and Evaluation of Inositol
Phosphorylceramide Synthase Inhibitors as New Antileishmanials

Abstract

Leishmaniasis is a Neglected Tropical Disease caused by the protozoan parasites of the genus Leishmania. Globally, an estimated 350 million are at risk of infection, and more than 12 million people are directly affected by the disease. With no effective vaccines available, the control strategy relies solely on chemotherapy. Current treatments for this disease suffer from multiple toxicities, increasing parasitic resistance, and are often expensive. Thus, there is an urgent need for the development of novel drug therapies with improved pharmacokinetic and safety profiles. Leishmania major inositol phosphorylceramide synthase (LmjIPCS), an essential enzyme involved in the biosynthesis of sphingolipids, has been identified as an attractive drug target. As this enzyme has no mammalian equivalent, selective drug candidates can be created with minimal host toxicity. A 1.8 million compound library was screened for activity against LmjIPCS and the parasite. Two 3H-benzazepine analogues, found to be potent LmjIPCS inhibitors, were selected for further investigation. Initial efforts focused on the synthesis of a series of 4-fluoroindole substituted benzazepine analogues, primarily with variations of the amine substituent and modifications of the N-alkyl linker. These compounds were most active against L. major promastigotes and several were identified as selective inhibitors of LmjIPCS. In an attempt to improve metabolic stability, the N-alkyl linker was extended providing benzazepine 74. With an EC50 of 1.42 μM, this analogue which exceed the inhibition of lead benzazepine 33a (EC50 = 3.23 μM) while maintaining LmjIPCS selectivity. In an effort to explore the necessity of the heterocycle on antileishmanial activity, phenethylamine based acyclic analogues were prepared. Although this more easily accessible acyclic series displayed moderate promastigote growth inhibition, the acyclic analogues more exhibited less species-dependent variation in activity. Overall, this investigation shows that 4-fluoroindole substituted benzazepine analogues are good candidates for further development of new antileishmanials.