Steroidal Alkaloids from Sarcococca saligna (Buxaceae): In Vitro and In Silico Evaluation of Their Cytotoxic Potential

Abstract

Sarcococca saligna (S. saligna), a medicinal shrub rich in therapeutic steroidal alkaloids (SAs), is ethnomedicinally used to treat ulcers, tumors, and wounds. In this study, to explore the anticancer potential of S. saligna, a combination of bioactivity-guided fractionation and isolation, an in vitro cytotoxic assay, and in silico analysis was used. The ethanolic extract of S. saligna (SL-01) was fractionated into butanol (SL-02), ethyl acetate (SL-03), hexane (SL-04), and water (SL-05) fractions. The extract and fractions, along with isolated compounds, were tested for anticancer activity against human cancer cell lines (colon, lung, and breast) using the sulforhodamine assay, with SL-03 displaying the strongest cytotoxicity in HT-29 colon cancer cells (IC₅₀ = 18.6 μM). The most active fraction SL-03 confirmed the presence of eight bioactive steroidal alkaloids via LC-ESI-QTOF-MS/MS analysis. Two SAs sarcorine C and salonine C isolated from SL-03 were structurally confirmed through NMR spectroscopy and exhibited selective cytotoxicity against HT-29 cells with minimal activity in noncancerous cell lines. The markedly lower IC₅₀ values of salonine C (5.21 μM) and sarcorine C (3.25 μM) highlight their potential as safer, more effective lead candidates for colon cancer therapy. Computational pharmacokinetics (SwissADME, ADMET analysis) predicted favorable drug-likeness, and DFT calculations provided electronic characteristics for both compounds. Moreover, molecular docking of both compounds with key cancer-associated targets CDK2, CYP17A1, Bcl-2, and MMP-2 showed stable binding. Additionally, extended 200 ns molecular dynamics simulations further validated the complexes, revealing stable RMSD, reduced SASA, favorable hydrogen bonding, and strong MM-GBSA binding free energies (△G_bind = −42.6 kcal·mol^–1 for sarcorine C vs −40.8 kcal·mol^–1 for roscovitine). These findings establish S. saligna as a promising source of anticancer steroidal alkaloids and report, for the first time, the selective cytotoxic activity of sarcorine C and salonine C against colon cancer cells, supported by integrated experimental and computational evidence.