Anti-piroplasmic Activity of Novobiocin as Heat Shock Protein 90 Inhibitor Against in-vitro Cultured Theileria Equi and Babesia Caballi Parasites

Abstract Background: Theileria equi and Babesia caballi are the causative agents for equine piroplasmosis (EP). Currently, imidocarb dipropionate (ID) is the only available drug for treating clinical form of EP. Serious side effects and uncompleted clearance of infection is major drawback of ID. Heat-shock proteins (HSP) play a vital role in the life cycle of these haemoprtozoa by way of preventing alteration in protein conformation. These HSPs are activated during transfer of EP sporozoites from tick vector (poikilotherm) to natural host (homeotherm) and helped it for survival. In this present study we have targeted the heat shock protein 90 pathway of T. equi and B. caballi by its inhibitor drug - novobiocin. Methods: Dose-dependent efficacy of novobiocin drug was observed on growth of T. equi and B. caballi in in-vitro culture. Cell cytotoxicity on host peripheral mononuclear cells (PBMCs) was also checked with different concentration of novobiocin. It was also checked for its haemolytic activity on equine erythrocyte (RBCs) by standard technique. In-vivo organ toxicity of novobiocin was also assessed in mice model with identified methods. Results: IC50 (50 % Inhibitory concentration) value of novobiocin against T. equi and B. caballi was 165 µM and 84.85 µM, respectively. Novobiocin significantly arrested the in-vitro growth of T. equi and B. caballi parasites at respective 100 μM and 200 μM drug concentration. In-vitro treated parasites become dead with distorted nuclear material and showed no further viability. The drug was found safe on the equine PBMCs and RBCs cell line even at 1000 µM concentration and CC50 (50 %, cytotoxicity concentration) values were 11.628 mM and 261.97 mM. A very high specific selective index (SSI) was also observed 70.47 and 1587 for respective equine PBMCs and RBCs. Organ specific biochemical markers and histopathological examination indicated no adverse effect of the drug at a dose rate of 50 mg/kg of body weight in mice model.Conclusions: The results clearly indicating the growth inhibitory efficacy of novobiocin against T. equi and B. caballi parasites and its safety on host cell lines with very high SI. Hence, it can be inferred that Theileria/Babesia Hsp-90 family are the potential drug targets worthy of further investigation.