Repurposed anticancer drugs disrupt cancer-like traits of Theileria annulata and suppress Leishmania donovani

Protozoan parasites remain a major threat to global health, affecting both humans and livestock. Theileria annulata, an apicomplexan parasite of cattle, transforms host leukocytes into a cancer-like state, while Leishmania donovani causes visceral leishmaniasis in humans. Given their reliance on host signaling and metabolic pathways, we hypothesized that FDA-approved anticancer drugs could be repurposed as antiparasitic agents. A library of 436 compounds was screened against T. annulata, yielding 130 hits at 10 µM, of which 63 exhibited minimal cytotoxicity toward healthy PBMCs. Secondary screening at 1 µM identified 28 potent inhibitors with > 50% activity. These compounds span diverse scaffolds, including taxanes, nucleoside analogues, antifolates, proteasome inhibitors, and kinase modulators, and target critical pathways such as apoptosis, autophagy, DNA damage response, cytoskeletal dynamics, NF-κB signalling, and tyrosine kinase activity. Notably, floxuridine, masitinib, paclitaxel, cabazitaxel, vinorelbine, maytansine, and bortezomib also suppressed L. donovani, highlighting cross-species efficacy. Target mapping revealed that the majority of active molecules disrupt hallmarks of cancer and parasite-transformed cells, including metabolic reprogramming, genome instability, and invasive phenotypes. Collectively, these findings underscore the value of oncology-derived drug libraries for antiparasitic discovery and identify promising candidates for further evaluation against T. annulata and L. donovani. 130 anticancer drugs reduced T. annulata infected cells viability, with 63 showing selective activity. Structural clusters identified: nucleoside analogues and taxane-class microtubule stabilizers. Secondary screening at 1 µM yielded 28 potent inhibitors with favourable drug-likeness and selectivity indices. Active compounds mapped to cancer hallmarks including deregulated energetics, genome instability, and invasion pathways. Seven compounds also inhibited Leishmania donovani, demonstrating cross-species antiparasitic potential.