Conditioned media and organic elicitors underpin the production of potent antiplasmodial metabolites by endophytic fungi from Cameroonian medicinal plants

Plasmodial resistance to artemisinin-based combination therapies emphasizes the need for new drug development to control malaria. This paper describes the antiplasmodial activity of metabolites produced by endophytic fungi of three Cameroonian plants. Ethyl acetate extracts of fungi cultivated on three different media were tested against Plasmodium falciparum chloroquine-sensitive (Pf3D7) and chloroquine-resistant (PfINDO) strains using the SYBR green florescence assay. Selected endophytes were further grown in potato dextrose broth supplemented with small organic elicitors and their extracts tested for activity. The effect of elicitors on de novo metabolite synthesis was assessed by reverse-phase HPLC. Activity screening of 81 extracts indicated that Aspergillus niger 58 (IC50 2.25–6.69 μg/mL, Pf3D7), Fusarium sp. N240 (IC50 1.62–4.38 μg/mL, Pf3D7), Phomopsis sp. N114 (IC50 0.34–7.26 μg/mL, Pf3D7), and Xylaria sp. N120 (IC50 2.69–6.77 μg/mL, Pf3D7) produced potent extracts when grown in all three media. Further culture of these endophytes in potato dextrose broth supplemented with each of the eight small organic elicitors and subsequent extracts screening indicated the extract of Phomopsis sp. N114 grown with 1% 1-butanol to be highly selective and extremely potent (IC50 0.20–0.33 μg/mL; SI > 666). RPHPLC profiles of extracts of Phomopsis sp. N114 grown with or without 1-butanol showed some peaks of enhanced intensities in the former without any qualitative change in the chromatograms. This study showed the ability of selected endophytes to produce potent and selective antiplasmodial metabolites in varied culture conditions. It also showed how the production of desired metabolites can be enhanced by use of small molecular weight elicitors.