Abstract
South Africa has one of the highest incidence rates of melanoma in the world. The lifetime risk of developing melanoma in South Africa is 1 in 314 men and 1 in 391 women. Patients with advanced melanoma have a very poor prognosis and many of the chemotherapies used to treat melanoma have undesirable side effects. Therefore, there is the need to identify a melanoma treatment that has minimal side effects. Medicinal plants are a valuable source of new drugs, drug leads and chemical entities and many of the cancer chemotherapeutic drugs currently in clinical use have been derived from plants. Sutherlandia frutescens is a medicinal plant indigenous to South Africa which has reported anti-cancer activities. Extracts of S. frutescens have been shown to have anti-proliferative apoptosis-inducing effects in a variety of cell lines. However, its effect on melanoma cells has not been studied. The aim of this study was to investigate whether an extract of S. frutescens could induce apoptosis in the A375 melanoma cell line and to outline the basic mechanism of action. The techniques used to evaluate this aim included the alamarBlue® assay, light microscopy, fluorescence microscopy, flow cytometry, western blot analyses and real-time PCR arrays. S. frutescens extract was found to induce apoptosis in the A375 cells as evidenced by an accumulation of hypoploid cells, apoptotic morphological features, phosphatidylserine translocation, nuclear condensation and fragmentation, caspase activation and the release of cytochrome c. The extract was also able to induce cell death in the presence of Z-VAD-fmk, which may be mediated by the apoptosis inducing factor. Additionally, S. frutescens extract altered the expression of a number of cancer-related genes. The data presented in this study largely support the hypothesis that S. frutescens extract exerts a cytotoxic effect on melanoma cells that involves the induction of apoptosis. The extract was able to induce extrinsic and intrinsic caspase-dependent apoptosis as well as caspase-independent cell death. Furthermore, gene analysis revealed several new molecular targets of S. frutescens extract. These include angiogenesis, metastasis, epithelial to mesenchymal transformation, hypoxia, cell cycle regulation and cell senescence. Taken together, the results of this study show that S. frutescens extract is effective in inducing apoptosis in malignant melanoma cells and indicates that further investigation into the clinical potential of the extract is warranted.
Ph.D. (Biochemistry)