Antiparasitic activity and molecular docking of canthin-6-one derivatives from LED- modulated Eurycoma longifolia...

Eurycoma longifolia (tongkat ali) is a widely recognized medicinal plant in Southeast Asia, valued for its bioactive alkaloids and quassinoids. Building on previous findings that light-emitting diode (LED) modulation enhances the antiproliferative activity of E. longifolia hairy root cultures (ELHRCs) crude extracts, this study aimed to isolate the specific active constituents, characterize their subtype-specific efficacy, and perform in silico analysis to evaluate potential interaction with proteases against Blastocystis ST3 and ST7. Through chromatographic purification and spectroscopic analysis (NMR, FT-IR, and GC-MS), two compounds canthin-6-one (1) and 9-methoxycanthin-6-one (2) were isolated from ELHRCs grown under various LED spectra for 10 weeks. Quantitative analysis revealed that compound 1 was specifically isolated from Red LED treatments. In contrast, compound 2 was successfully isolated across all treatments, with the highest yield (1.00%) obtained under Mint Green LED illumination. In vitro assays demonstrated that both compounds exhibited dose-dependent inhibitory activity. Using nonlinear sigmoidal dose-response modelling, the values for compound 2 were determined to be 0.0427 mg/mL (ST3) and 0.0433 mg/mL (ST7), while compound 1 exhibited values of 0.0482 mg/mL (ST3) and 0.0603 mg/mL (ST7). Molecular docking studies targeting a cysteine protease surrogate revealed binding affinities of - 6.9 kcal/mol and - 7.3 kcal/mol for compounds 1 and 2, respectively. Although the standard drug metronidazole exhibited higher potency in vitro, these results indicate that LED-stimulated ELHRCs are a viable source for the production of canthin-6-one alkaloids with promising antiparasitic potential.