Drug repositioning as a route to anti-malarial drug discovery: preliminary investigation of the in vitro anti-malarial efficacy of emetine dihydrochloride hydrate

Background: Drug repurposing or repositioning refers to the usage of existing drugs in diseases other than those it was originally used for. For diseases like malaria, where there is an urgent need for active drug candidates, the strategy offers a route to significantly shorten the traditional drug development pipelines. Preliminary high-throughput screens on patent expired drug libraries have recently been carried out for Plasmodium falciparum. This study reports the systematic and objective further interrogation of selected compounds reported in these studies, to enable their repositioning as novel stand-alone anti-malarials or as combinatorial partners. Methods: SYBR Green flow cytometry and micro-titre plate assays optimized in the laboratory were used to monitor drug susceptibility of in vitro cultures of P. falciparum K1 parasite strains. Previously described fixed-ratio methods were adopted to investigate drug interactions. Results: Emetine dihydrochloride hydrate, an anti-protozoal drug previously used for intestinal and tissue amoebiasis was shown to have potent inhibitory properties (IC50 doses of similar to 47nM) in the multidrug resistant K1 strain of P. falciparum. The sum 50% fractional inhibitory concentration (Sigma FIC50, (90)) of the interaction of emetine dihydrochloride hydrate and dihydroartemisinin against the K1 strains of P. falciparum ranged from 0.88-1.48. Conclusion: The results warrant further investigation of emetine dihydrochloride hydrate as a potential stand-alone anti-malarial option. The interaction between the drug and the current front line dihydroartemisinin ranged from additive to mildly antagonistic in the fixed drug ratios tested.