Combined pitavastatin and dacarbazine treatment activates apoptosis and autophagy resulting in synergistic cytotoxicity in melanoma cells

Abstract

Abstract. Melanoma is an aggressive skin cancer and its incidence is increasing faster than any other type of cancer. Whilst dacarbazine (DTIC) is the standard chemotherapy for metastatic melanoma, it has limited success. Statins, including pitavastatin, have been demonstrated to have a range of anticancer effects in a number of human cancer cell lines. The present study therefore explored the anti-cancer activity of combined DTIC and pitavastatin in A375 and WM115 human melanoma cells. Cell survival assays demonstrated that combined DTIC and pitavastatin treatment resulted in synergistic cell death. Cell cycle analyses further revealed that this combined treatment resulted in a G1 cell cycle arrest, as well as a sub-G1 population, indicative of apoptosis. Activation of apoptosis was confirmed by Annexin V-fluorescein isothiocyanate/propidium iodide double-staining and an increase in the levels of active caspase 3 and cleaved poly (ADP-ribose) polymerase. Furthermore, it was demonstrated that apoptosis occurs through the intrinsic pathway, evident from the release of cytochrome c. Finally, combined DTIC and pitavastatin treatment was demonstrated to also activate autophagy as part of a cell death mechanism. The present study provides novel evidence to suggest that the combined treatment of DTIC and pitavastatin may be effective in the treatment of melanoma. IntroductionMelanoma is a particularly aggressive skin cancer and its incidence is increasing faster than any other cancer worldwide (1). At present, the 10-year survival rate of patients diagnosed with advanced (stage IV) metastatic melanoma is <10% (2), which highlights the importance of early detection and treatment. The Food and Drug Administration approved the chemotherapeutic agent dacarbazine (DTIC) for the treatment of metastatic melanoma in 1975, and it remains the only licensed chemotherapeutic agent in use today (1). DTIC is a methylating agent which causes DNA damage, cell cycle arrest and apoptosis. Despite this, only 2% of all patients with metastatic melanoma receiving this treatment demonstrate a significant response and only 11.2% demonstrate a partial response (3). Resistance to DTIC has been associated with the upregulation of pro-survival signals and anti-apoptotic molecules in cancer cells. Despite its moderate effects, DTIC continues to be the standard treatment for metastatic melanoma as no other chemotherapeutic treatment has been demonstrated to have a significantly increased chance of survival when compared with DTIC (4,5). Provided the limited efficacy of the current metastatic melanoma chemotherapies in addition to the increasing incidence of melanoma cases, there appears to be a need for the development of more effective treatment strategies.Statins are a group of drugs commonly used for the reduction of cholesterol levels (6). They work by inhibiting 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, a critical enzyme in the mevalonate pathway, which is responsible for cholesterol synthesis (6,7). In addition, statins have been de...

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“…The lysates were collected, and the protein concentrations were determined using Bradford's reagent (Bio-Rad Laboratories, Inc.), according to the manufacturer's instructions and using albumin as a standard. A total of 20 µg protein was separated by 8–15% SDS-PAGE, and transferred to a Hybond ECL nitrocellulose membrane (GE Healthcare, Chicago, IL, USA) (17). Following blocking for 1 h at room temperature with PBS containing 0.05% Tween-20 and 5% powdered skim milk, membranes were incubated overnight with primary antibodies (1:1,000) at 4°C.…”

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