Blockade of phosphorylation of mitogenic signaling pathways: medicinal plant approach.

Carissa edulis (Vahl) has been used in traditional medicine for the management of fever, sickle cell disease, epilepsy, viral, bacterial, parasitic infections and cancer for many years. The present study is aimed at evaluating the antitumour properties of petroleum ether fraction (PEF) of the standardized ethanol root bark extract of Carissa edulis. Cell viability (kill study) was assessed using U1242 glioblastoma cell lines and the mechanisms involved in the cell death were determined via western blotting (protein phosphorylation). The fraction (PEF) significantly (p<0.001) and dose dependently decreased cell viability of the glioblastoma multiforme (GBM) cells, the lower concentration, 62.5 µg/ml offered 30% reduction while 500 µg/ml gave 83.2%; IC50 was found to be 127.27 µg/ml. The epithelial growth factor (EGF) increased cell count from 2.98 × 105 dimethyl sulphoxide (DMSO) to 3.69 × 105 cells/ml. Also, the fraction (PEF) showed dose dependent and significant (p<0.001) reduction in the GBM U1242 cells proliferation driven by epidermal growth factor (EGF); the % cell kill were 31.98% at 62.5 µg/ml, (the lowest concentration) while 500 µg/ml gave 92.68% and the IC50 was found to be 107.90 µg/ml. In the phosphorylation studies, PEF at the downstream, blocked the phosphorylation of mitogen activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) mediated by both EGF and phorbol 12-myristate 13-acetate (PMA) transactivation. The PEF had no effect on the platelet-derived growth factor (p-PDGF) transactivation of p-EGF 1068 at receptor level, but significantly blocked p-MAPK and protein kinase B (Akt) phosphorylation at downstream. It might be concluded that the petroleum ether fraction of the standardized ethanol root bark extract of C. edulis contains biologically active principles that have anti-glioblastoma cells growth. The mechanisms involved are blockade of phosphorylation of mitogenic signaling pathways such as MAPK, Akt and NF-κB and induction of apoptosis.