Cytotoxic effect of <i>Spatholobus littoralis</i> extract on breast cancer cells by in vitro and prediction of the mechanism of activity against estrogen receptors (ER-α and ER-β) by in silico

Introduction: Spatholobus littoralis is widely used as an anticancer herbal medicine in Kalimantan, Indonesia. This study aims to determine the cytotoxic effect of S. littoralis on breast cancer cells in vitro and predict the mechanism of its activity on the estrogen receptors (ER) in silico. Methods: Dry wood of S. littoralis was extracted using ethanol solvent by maceration and fractionated using n-hexane, chloroform, and ethyl acetate. The cytotoxic assay was evaluated using MTT reagent in T47D and 4T1 cells. Prediction of the interaction mechanism of phenolic compounds from the genus Spatholobus with ER-α and ER-β was carried out in silico. Results: The results showed that the ethanolic extract of S. littoralis did not show a cytotoxic effect on T47D cells, but showed weak toxicity on 4T1 cells. Furthermore, n-hexane, chloroform, and ethyl acetate fractions of S. littoralis showed strong to moderate cytotoxic effects on T47D and 4T1 cells. In silico test results showed that 3’-4’-7-trihydroxy flavone was a phenolic compound with the highest binding energy compared to the ER native ligand Genistein in ER-α (-10.2 kcal/mol) and ER-β (-10.9 kcal/mol). The 3’-4’-7-trihydroxy flavone binding site in ER-α was bound to amino acid residues Arg394, Glu353, and Leu387, while in ER-β it was found at Arg346, Glu305, and Leu339. Conclusion: These findings indicate that S. littoralis contains phenolic compounds that can inhibit the growth of breast cancer cells, so it may have the potential to be developed as a new drug for breast cancer.