Lead optimisation of dehydroemetine for repositioned use in malaria
Drug repositioning offers an effective alternative to de novo drug design to tackle the urgent need for novel anti-malarial treatments. The anti-amoebic compound, emetine dihydrochloride, has been identified as a potent in-vitro inhibitor of the multi-drug resistant strain K1 of Plasmodium falciparum (IC50: 47 nM + 2.1 nM). 2,3-dehydroemetine, a synthetic analogue of emetine dihydrochloride has been claimed to have less cardiotoxic effects than emetine. The structures of two diastereoisomers of 2,3-dehydroemetine were modelled on the reported emetine binding site on cryo-EM structure 3J7A and it was found that (-)-R,S-dehydroemetine mimicked the bound pose of emetine more closely than (-)-S,S-dehydroisoemetine. (-)-R,S-dehydroemetine was also found to be highly potent against the multi-drug resistant K1 strain of P. falciparum in comparison with (-)-S,S-dehydroisoemetine, which loses its potency due to the change of configuration at C-1. In addition to its effect on the asexual erythrocytic stages of P. falciparum, the compounds exhibited gametocidal properties with no cross-resistance against any of the multi-drug resistant strains tested. Drug interaction studies showed (-)-R,S-dehydroemetine to have synergistic antimalarial activity with atovaquone and proguanil. Emetine dihydrochloride, and (-)-R,S-dehydroemetine failed to show any inhibition of the hERG potassium channel and displayed atovoquone-like activity on the mitochondrial membrane potential.