Purified solasodine from Solanum mauritianum Scop. and its molecular mechanism of antimetastatic potential

Breast cancer has been identified as one of the most common type of cancer among female human population. General treatment approaches against breast cancer includes radio, chemo or hormonal therapy. Unfortunately, most of these approaches ameliorate the target and evoke adverse side effects. Phytochemicals including alkaloids are reported to alleviate ailments with no or little side effects. Bug weed (Solanum mauritianum Scop.), an evergreen medium sized tree of Solanaceae, a native of South America was used for treating different pain disorders. Glycoalkaloid solasodine was isolated and purified from S. mauritianum and was identified by 1H NMR. Cytotoxic evaluation by MTT assay against MCF-7 breast cell lines revealed significant inhibition. In order to confirm the antimetastatic property and to elucidate the mode of action, molecular targets and signalling pathways, transmission electron microscopy and western blot analysis of the cell cycle regulatory proteins such as p53, p21, cyclin D1, cyclin E and molecules involved in apoptosis (PARP, procaspase 7, 8 and 9) and Bcl-2 family members (Bcl-2, Bcl-xL, Bax and Bak) were analysed. Solasodine treated MCF-7 cells showed varying degrees of cellular damage. Early apoptotic cells have degraded DNA with cell blebbing. Late apoptotic and necrotic cells showed fragmented DNA with reddish and green staining. Solasodine exhibited an upregulation of p53 and p21 proteins. Meanwhile, a decrease in the expression levels was noticed with cyclin D1 and E within 12 h of treatment. Procaspase-7, 8 and 9 showed reduced expression on solasodine application, suggesting the alkaloid has a triggering effect on the induction of both intrinsic and extrinsic apoptotic pathways. Interestingly, procaspase-9 was up regulated after 48 h following an initial down regulation. The results proposes that the activation of caspase-9 begins earlier compared to caspase-7 and 8. Further, solasodine elevated the expression of cleaved PARP moderately (24 h). In addition, solasodine treated MCF-7 cells showed significant decline in the expression of Bcl-2 and Bcl-xL (anti-apoptotic protein) after 48 h, with an increase in Bax and Bak (pro- apoptotic protein) expression. Therefore it can be interpreted that the solasodine inhibited the cell cycle at G2/M and the anti-apoptotic signals and promoted pro-apoptotic signals, thereby the mitochondrial permeability.