Synergistic effects of Lorestanol, an ursane-type triterpenoid from Euphorbia aleppica, in combination with cisplatin on apoptosis in cisplatin-resistant ovarian cancer cell lines

Lorestanol, an ursane-type triterpenoid extracted from Euphorbia aleppica, was evaluated for its cytotoxic and apoptotic effects both alone and in combination with cisplatin on the cisplatin-sensitive A2780-WILD and cisplatin-resistant A2780-RCIS ovarian cancer cell lines. MTT assay results showed that cisplatin had IC₅₀ values of 10.71 μM in A2780-WILD and 86.49 μM in A2780-RCIS, confirming high resistance in the latter. Lorestanol alone exhibited cytotoxicity with IC₅₀ values around 45 μM in both lines. Notably, the combination of Lorestanol and cisplatin significantly enhanced cytotoxicity, reducing cell viability from 97.33 % to 7.50 % in A2780-WILD and from 60.67 % to 23.89 % in A2780-RCIS. Combination index (CI) values indicated strong synergism (0.9 for A2780-WILD and 0.65 for A2780-RCIS), while drug reduction index (DRI) values showed decreased cisplatin dosage requirements (1.25 and 3.14, respectively).

Apoptosis analysis via Annexin V/PI staining revealed up to 88.6 % apoptosis in A2780-WILD cells treated with the combination. Mechanistically, the combination induced apoptosis through endoplasmic reticulum (ER) stress, evidenced by elevated expression of Caspase-12 and CHOP, along with increased GRP78 and PERK expression. Additionally, the combination downregulated drug resistance genes such as SOD1 and MRP1, particularly in resistant cells. Molecular docking of Lorestanol with MRP1 further supported its binding within the substrate site, highlighting interactions with key amino acid residues. These findings suggest that Lorestanol significantly enhances cisplatin efficacy and may help overcome chemotherapy resistance in ovarian cancer.