Current anti-malarial treatments are failing due to the emergence of resistance to the only frontline anti-malarials available, the artemisinins, and therefore identification of novel anti-malarials is urgently needed. The aminobenzimidazoles (ABIs) are a novel class of anti-malarial that were identified recently. These compounds have excellent potency against the blood stage of the malaria parasite, Plasmodium falciparum, and retain activity against a number of strains that are resistant to other known drugs. However, the mechanism of action of these compounds remains unknown, limiting the scope for further development.
A number of ABI derivatives were synthesised and tested to identify analogues with improved potency against P. falciparum and to develop our knowledge of the structure-activity relationships of these compounds. More than 15 active analogues were identified with sub-micromolar potency. The most potent compound demonstrated an IC50 of 41 nM, a two-fold increase in potency when compared to the original ABI (86 nM).
Untargeted metabolomics analysis was performed on ABI-treated P. falciparum-infected red blood cells to determine its mechanism of action. Following 1 h incubation, over 600 metabolite features were detected. Multivariate analysis revealed clustering of ABIs with mefloquine and dihydroartemisinin, primarily due to the depletion of haemoglobin-related small peptides. Untargeted peptidomics were also performed to analyse the abundance of longer peptides associated with haemoglobin degradation; this revealed a significant depletion of all haemoglobin-related peptides following treatment.
ABIs are a novel class of anti-malarial compounds with attractive in vitro potency and activity against known drug-resistant strains of P. falciparum. Multi-omics analysis suggests that they act to inhibit the breakdown of haemoglobin, a key pathway for the growth of the malaria parasite inside the host red blood cell. Further work will investigate the molecular mechanism(s) through which this inhibition occurs.