Evaluation of the cytotoxic potential of a new pentacyclic triterpene from Rhododendron arboreum stem bark

Context: Traditionally, Rhododendron arboreum Sm. (Ericaceae) is a very important medicinal plant having oxytocic, estrogenic, anti-inflammatory, analgesic and hepatoprotective activities; it also inhibits the prostaglandin synthetase. Objectives: This study determines the cytotoxic potential of 15-oxoursolic acid isolated from R. arboreum against selected human cancer cell lines. Materials and methods: Extraction from stem bark (5 kg) of R. arboreum was performed with methanol, which was successively partitioned into hexane, dichloromethane and ethyl acetate fractions, respectively. The new antitumor agent [15-oxoursolic acid (1)] was isolated from ethyl acetate fraction through column chromatography. Structure elucidation of new compound was performed through extensive spectroscopy i.e., IR, MS and 1D and 2D NMR. Cytotoxicity of isolated compound was determined at doses 5–100 μM for a period of 72 h on specified human cancer cell lines [renal cell carcinoma (A498), non-small cell lung (NCI-H226), squamous cell carcinoma (H157) and human ovarian carcinoma (MDR-2780AD)]. Results: Structure of isolated compound was characterized as 15-oxoursolic acid on the basis of various extensive spectroscopic techniques. 15-Oxoursolic acid revealed considerable anticancer activity with IC(50) values of 2.3 ± 0.1 μM, 4.9 ± 0.2 μM, 9.2 ± 0.2 μM and 10.3 ± 0.1 μM against MDR 2780AD, Hep G2, H157 and NCI-H226, respectively, while in the case of A498, the activity was good (IC(50) 32.8 ± 1.2 μM). Conclusions: This study highlighted the potential of 15-oxoursolic acid to be further explored as a new lead compound for cancer chemotherapy.