Exploring the mode of action of a suit of novel antileishmanials

Abstract

The control of the neglected tropical disease leishmaniasis relies on out-dated, toxic and increasingly ineffective therapeutical drugs. As no vaccines exist, novel drugs are urgently needed to overcome emerging parasite-drug-resistance and reduce drug toxicity. This thesis aimed to contribute to the identification of novel therapeutic targets for Leishmania drug development.

Antileishmanial compounds identified in a GSK phenotypic-screen against Leishmania donovani (Leish-box) and Trypanosoma cruzi (Chagas-box), and currently not actively researched for drug discovery, were investigated to elucidate their mode of action (MoA). A novel pipeline approach was developed for this purpose, combining cellular research techniques and technologies in three phases: (1) triaging compounds by potency (against cutaneous leishmaniasis species), rate-of-kill and medicinal chemistry accessibility; (2) characterising mode of resistance of in vitro evolution-derived mutants via Illumina sequencing and cross-resistance studies against clinical antileishmanials; (3) investigating compound protein targets through thermal proteome profiling, a cutting-edge technique in this area.

Two candidate compounds were triaged down from seventeen. Compound 4 (Leish-box) demonstrated a fast rate-of-kill and potent activity in Leishmania species (promastigotes) and did not facilitate in vitro generation of resistance. Despite demonstrating a slow rate- of-kill and moderate activity in Leishmania, Compound 11 (Chagas-box) was selected for further investigation given its high activity in T. cruzi. Both compounds had favourable physicochemical properties, and predictions of pharmacokinetics and medicinal chemistry accessibility. No cross-resistance was found, suggesting these compounds have potential to reveal novel MoAs and cellular targets.

The analyses of the resistant mutants generated suggested the involvement of lipid metabolism, including the Kennedy pathway, and ubiquinone/terpenoid metabolism in the MoA of both compounds against L. major and L. mexicana. Further investigation of these pathways could lead to discovery of molecular targets for novel antileishmanial-drug development. The results also present a novel pipeline as a potential tool for drug development for protozoan parasites.