Evaluating the antiplasmodial activity of synthetic and natural product libraries against intraerythrocytic Plasmodium falciparum

Mobley, Rebecca May

Abstract

Malaria continues to cause great global health concerns despite efforts for control and elimination. The emergence of resistance to components of the frontline artemisinin combination therapy highlights the urgent need for novel malaria therapeutics and innovative screening approaches to seed the drug discovery pipeline. Rapid triaging of large compound libraries for potent and efficacious antiplasmodial action offers a valuable tool in the drug discovery process. This study aims to explore synthetic and natural product libraries as sources for candidate antimalarials. Three novel libraries will be investigated here; a synthetic heparinmimetic (HM) sulphonated polymer library, an over sulphated hyaluronic acid (HA) library and a PhytoQuest (a UK small-to-medium enterprise) natural product library.
The synthetic HM library and a small library of over sulphated HAs were explored for heparinmimetic antiplasmodial activity. Heparin has been explored as an adjunct therapy for severe malaria due to its anti-rosetting/-cytoadhesion and growth inhibitory (through blocking of merozoite invasion) activity. Recent reports of merozoite egress blocking activity by heparin highlight a potential new or additional inhibitory phenotype of heparin. The inhibitory activity of heparin has been associated with its negative charge and sulphate groups within its structure. In this study, the sulphonated HM and the sulphated HA library both exhibited in vitro heparinmimetic antiplasmodial action against two genetically distinct parasite strains (Dd2luc and NF54luc), equivalent to or better than heparin in some instances, with comparably lower anticoagulation activity. Compounds HA2 and HM21 (Poly(SS-co-SPM)1:2) were identified as lead compounds from each library, with consistent and relatively potent antiplasmodial activity (EC50: 3 and 7.6μg/mL, respectively). Microscopic staging analysis and live video microscopy showed no apparent inhibitory effect on merozoite egress by heparin or the heparinmimetic compounds but complete inhibition of merozoite invasion was observed in the presence of heparin, HM21 and HA2. This study evidenced merozoite invasion, with likely multi-targeted inhibition, as the key inhibitory mechanism of heparin and heparin-mimetics.
Previously, a modified Bioluminescence Relative Rate of Kill (mBRRoK) assay was developed as a screening tool to quickly triage large compound libraries, of known antiplasmodial action, while simultaneously extracting potency and rate of kill data with the aim to select compounds with potent and rapid-acting rate of kills. The utility of the mBRRoK screening method was extended in this study to screen a PhytoQuest natural product library containing a large number of compounds from fungi and actinomyces, of unknown antiplasmodial potential, for potent antiplasmodial leads with both rapid- and slow-acting rates of kill to potentially comprise several components of malaria combination therapy. The mBRRoK assay was used in this study to identify 34 compounds, with both fast- and slow-acting rate of kill, with reproducible antiplasmodial activity against parasite strains with different resistance profiles (Dd2luc and NF54luc). Subsequent in vitro antiplasmodial screening methods and HepG2 cytotoxicity highlighted four of these compounds as lead candidates with selective (SI: >8 to >211) and potent (EC50:94nM-2.4μM) antiplasmodial activity. One compound (100657) was identified as cladosporin, known to have antiplasmodial action. Two structurally related compounds (101158 and 101160) and another structurally unrelated compound (101173) with undetermined structures were highlighted as potentially novel sources of antiplasmodial action.

Citation

Mobley, R. M. (2024). Evaluating the antiplasmodial activity of synthetic and natural product libraries against intraerythrocytic Plasmodium falciparum. (Thesis). Keele University. Retrieved from https://keele-repository.worktribe.com/output/853179

• Thesis Type: Thesis
• Deposit Date: Jun 20, 2024
• Publicly Available Date: Jun 20, 2024
• Public URL: https://keele-repository.worktribe.com/output/853179
• Award Date: 2024-06