A bio-guided investigation of Mitragyna inermis (Willd) O. Kuntze (Rubiaceae) unveils natural product isolates with potent cross-activity against sensitive and multidrug resistant Plasmodium falciparum strains in vitro.

ETHNOBOTANICAL RELEVANCE: Malaria remains a significant global health challenge, especially in sub-Saharan Africa, with rising resistance to artemisinin-based therapies highlighting the urgent need for new, effective, and safer treatments from medicinal plants which have been used by the indigenous people.

AIM OF THE STUDY: This study investigates the antiplasmodial potential of natural products from Mitragyna inermis.

METHODS

Crude extracts from the stem bark and twigs of Mitragyna inermis were prepared using various solvents (water, ethanol/water, ethanol, and methanol) and tested for activity against Plasmodium falciparum strains Dd2 and 3D7 using the SYBR Green I-based fluorescence assay. Cytotoxicity was assessed on Vero cells and erythrocytes employing the resazurin reduction and hemolysis methods, and promising extracts further purified using column chromatography, and the afforded compounds characterized using spectroscopic methods. The pharmacokinetic properties of two promising compounds (ellagic acid and arjungenin) were predicted using Swiss ADME software.

RESULTS

The methanolic and ethanol/water extracts showed highly potent antiplasmodial activity (IC50 < 3 μg/mL) and acceptable selectivity (SI > 10). Among the isolated and identified compounds, only compound 1 (ellagic acid) exhibited potent cross-activity (IC50 0.84-1.62 μg/mL (2.77-5.36 μM) against drug-susceptible Plasmodium falciparum 3D7 (Pf3D7) and multidrug-resistant (PfDd2, PfINDO, PfW2, PfK1) Plasmodium falciparum strains. These compounds were isolated from Mitragyna inermis for the first time. Predictably, ellagic acid (1) adheres to the Lipinski's five rules, demonstrating good oral bioavailability, water solubility, high gastrointestinal absorption, non-substrate of permeability glycoprotein (P-gp), non-inhibition of cytochrome P450 (CYP450) and ease of synthesis, indicating safety and promising therapeutic potential. Additionally, among the five unidentified compounds (5-9), compounds 5, 6, 7 and 8 were the overall most potent with IC50 values ranging from 0.21 to 5.38 μg/mL against at least 3 plasmodial strains.

CONCLUSION

Beyond ellagic acid which showed a promising antiplasmodial activity and acceptable ADME profile, the potency of compounds 5-8 warrants a detailed investigation as promising starting points for antimalarial drug discovery.