Acceleration of pro-caspase-3 maturation and cell migration inhibition in human breast cancer cells by phytoconstituents of Rheum emodi rhizome extracts

The aggressive nature of estrogen receptor (ER)-negative breast cancer subtype obligates for innovative targeted therapies. The present study aimed to investigate the phytoconstituents and specific anticancer activities of Rheum emodi rhizome, a known food source used locally to treat various ailments. Petroleum ether extracts (hot [PHR] and cold [PCR]) of R. emodi, exhibited significant free radical scavenging potentials through DPPH and reducing power assays, rendering them as good sources of antioxidants. The extracts, PHR and PCR had shown significant (P < 0.05) cancer-cell-specific cytotoxicity in the assayed cells (MDA-MB-231 [breast carcinoma] and WRL-68 [non-tumoral]) at 100 μg/ml, and 50 and 100 μg/ml concentrations respectively. Extracts also induced fervent apoptosis in ER-negative cells (MDA-MB-231) compared to ER-positive subtype (MCF-7), and found to involve CPP32/caspase-3 in its apoptosis induction mechanism. Moreover, extracts had an inevitable potential to inhibit the migration of metastatic breast cancer cells (MDA-MB-231) in vitro. Further, the active principles of extracts were identified through HPLC and GC-MS analysis to reveal major polyphenolics, 4,7-Dimethyl-(octahydro)indolo[4,3-fg]quinolin-10-one, 5-Oxo-isolongifolene, Valencene-2, and other quinone, quinoline and anthraquinone derivatives. The extracts are thus good candidates to target malignant ER-negative breast cancer, and the identified phytoconstituents could be eluted in further exploratory studies for use in dietary-based anti-breast cancer therapies.