Natural products offer an abundant source of diverse novel scaffolds that inspires development of next generation anti-malarials. With this vision, a library of scaffolds inspired by natural biologically active alkaloids was synthesized from chiral bicyclic lactams with steps/scaffold ratio of 1.7:1. On evaluation of library of scaffolds for their growth inhibitory effect against malaria parasite we found one scaffold with IC50 in low micro molar range. It inhibited parasite growth via disruption of Na+ homeostasis. P-type ATPase, PfATP4 is responsible for maintaining parasite Na+ homeostasis and is a good target for anti-malarials. Molecular docking with our scaffold showed that it fits well in the binding pocket of PfATP4. Moreover, inhibition of Na+-dependent ATPase activity by our potent scaffold suggests that it targets parasite by inhibiting PfATP4, leading to ionic imbalance. However how ionic imbalance attributes to parasite’s death is unclear. We show that ionic imbalance caused by scaffold 7 induces autophagy that leads to onset of apoptosis in the parasite evident by the loss of mitochondrial membrane potential (ΔΨm) and DNA degradation. Our study provides a novel strategy for drug discovery and an insight into the molecular mechanism of ionic imbalance mediated death in malaria parasite.
BackgroundMalaria remains the world’s most important devastating parasitic disease. Of the five species of Plasmodium known to infect and cause human malaria, Plasmodium falciparum is the most virulent and responsible for majority of the deaths caused by this disease. Mainstream drug therapy targets the asexual blood stage of the malaria parasite, as the disease symptoms are mainly associated with this stage. The prevalence of malaria parasite strains resistance to existing anti-malarial drugs has made the control of malaria even more challenging and hence the development of a new class of drugs is inevitable.MethodsScreening against different drug resistant and sensitive strains of P. falciparum was performed for few bicyclic lactam-based motifs, exhibiting a broad spectrum of activity with low toxicity generated via a focussed library obtained from diversity oriented synthesis (DOS). The synthesis and screening was followed by an in vitro assessment of the possible cytotoxic effect of this class of compounds on malaria parasite.ResultsThe central scaffold a chiral bicyclic lactam (A) and (A’) which were synthesized from (R)-phenylalaninol, levulinic acid and 3-(2-nitrophenyl) levulinic acid respectively. The DOS library was generated from A and from A’, by either direct substitution with o-nitrobenzylbromide at the carbon α- to the amide functionality or by conversion to fused pyrroloquinolines. Upon screening this diverse library for their anti-malarial activity, a dinitro/diamine substituted bicyclic lactam was found to demonstrate exceptional activity of >85% inhibition at 50 μM concentration across different strains of P. falciparum with no toxicity against mammalian cells. Also, loss of mitochondrial membrane potential, mitochondrial functionality and apoptosis was observed in parasite treated with diamine-substituted bicyclic lactams.ConclusionsThis study unveils a DOS-mediated exploration of small molecules with novel structural motifs that culminates in identifying a potential lead molecule against malaria. In vitro investigations further reveal their cytocidal effect on malaria parasite growth. It is not the first time that DOS has been used as a strategy to identify therapeutic leads against malaria, but this study establishes the direct implications of DOS in scouting novel motifs with anti-malarial activity.Electronic supplementary materialThe online version of this article (doi:10.1186/1475-2875-13-467) contains supplementary material, which is available to authorized users.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.