Background: Resistance of Plasmodium falciparum against common anti-malarial drugs emphasizes the need of alternative and more effective drugs. Synthetic derivatives of 1-(heteroaryl)-2-((5-nitroheteroaryl)methylene) hydrazine have showed in vitro anti-plasmodial activities. The present study aimed to evaluate the molecular binding and anti-plasmodial activity of synthetic compounds in vivo.
Methods: The molecular docking was used to study the binding of compounds to haem and Plasmodium falciparum lactate dehydrogenase (PfLDH). Acute toxicity of the synthetic compounds was evaluated based on the modified up & down method. The anti-plasmodial activity of the compounds was conducted by the two standard tests of Peters' and of Rane, using chloroquine-sensitive Plasmodium berghei in mice. Also, the toxicity to the internal organs of mice was evaluated on the seventh day after the treatment in addition to the histopathology of their liver. Compound 3 that showed high activity in the lowest dose was selected for further pharmacodynamic studies.
Results: According to the docking studies, the active site of PfLDH had at least four common residues, including Ala98, Ile54, Gly29, and Tyr97 to bind the compounds with the affinity, ranging from - 8.0 to - 8.4 kcal/mol. The binding mode of ligands to haem revealed an effective binding affinity, ranging from - 5.1 to - 5.5 kcal/mol. Compound 2 showed the highest % suppression of parasitaemia (99.09%) at the dose of 125 mg/kg/day in Peters' test. Compound 3, with 79.42% suppression, was the best in Rane's test at the lowest dose (31 mg/kg/day). Compound 3 was confirmed by the pharmacodynamic study to have faster initial parasite elimination in the lowest concentration. The histopathology of the livers of mice did not reveal any focal necrosis of hepatocytes in the studied compounds.
Conclusions: The docking studies verified Pf LDH inhibition and the inhibitory effect on the haemozoin formation for the studied compounds. Accordingly, some compounds may provide new avenues for the development of anti-malarial drugs without liver toxicity, although further studies are required to optimize their anti-plasmodial activity.
Keywords: Anti-plasmodial activity; Docking study; Histopathology; Pharmacodynamics; Plasmodium berghei; Quinazoline; Quinoline.