Abstract
Melanoma is an aggressive skin cancer. Unfortunately, there is currently no chemotherapeutic agent available to significantly prolong the survival of the most patients with metastatic melanomas. Here we report that the Ginkgo biloba extract (EGb761), one of the most widely sold herbal supplements in the world, potently induces apoptosis in human melanoma cells by disturbing the balance between pro- and anti-apoptosis Bcl-2 family proteins. Treatment with EGb761 induced varying degrees of apoptosis in melanoma cell lines but not in melanocytes. Induction of apoptosis was caspase-dependent and appeared to be mediated by the mitochondrial pathway, in that it was associated with reduction in mitochondrial membrane potential and activation of Bax and Bak. Although EGb761 did not cause significant change in the expression levels of the BH3-only Bcl-2 family proteins Bim, Puma, Noxa, and Bad, it significantly downregulated Mcl-1 in sensitive but not resistant melanoma cells, suggesting a major role of Mcl-1 in regulating apoptosis of melanoma cells induced by EGb761. Indeed, siRNA knockdown of Mcl-1 enhanced EGb761-induced apoptosis, which was associated with increased activation of Bax and Bak. Taken together, these results demonstrate that EGb761 kills melanoma cells through the mitochondrial apoptotic pathway, and that Mcl-1 is a major regulator of sensitivity of melanoma cells to apoptosis induced by EGb761. Therefore, EGb761 with or without in combination with targeting Mcl-1 may be a useful strategy in the treatment of melanoma.
Highlights
The incidence of melanoma continues to rise in many countries, and it has become one of the main causes of cancer-related morbidity and mortality all over the world [1]
Activated Bax and Bak could hardly be detected in Mel-RM cells at 16 hours after treatment. These results suggest that the oligomerization of Bax and Bak and subsequent reduction in membrane potential (MMP) are involved in apoptosis induced by EGb761, further confirming the role of the mitochondrial apoptotic pathway in EGb761-induced apoptosis in melanoma cells
Since Mcl-1 was differentially regulated by EGb761 in Mel-RM and Mel-AT cells with different sensitivity to EGb761-inudced apoptosis, we further study the role of Mcl-1 in regulation of Columns, mean of three individual experiments; bars, SEM. * Present p
Summary
The incidence of melanoma continues to rise in many countries, and it has become one of the main causes of cancer-related morbidity and mortality all over the world [1]. Surgery is the most effective treatment of melanoma at early stages. There is currently no PLOS ONE | DOI:10.1371/journal.pone.0124812. EGb761 Induced Apoptosis in Melanoma curative therapy once the disease spreads beyond the primary site. Treatment of metastatic melanomas continues to pose a therapeutic challenge [2]. This is closely related to resistance of melanoma cells to apoptosis induced by conventional chemotherapeutics as well as other biological agents [3–5]. Understanding of mechanisms responsible for the resistance is critical for identification of new therapeutic targets and development of novel treatment approaches [6–8]
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