Abstract 336: IL-6 primes melanoma cells from early stages to statin induced apoptosis

Abstract

Abstract Introduction: Statins trigger apoptosis in tumour cells in vitro and, particularly, melanoma cells are susceptible to statin induced apoptosis. Growth of normal melanocytes and early stage melanoma can be inhibited by IL-6, whereas metastatic melanoma cells are mostly resistant to the anti-proliferative effects of IL-6. It has been shown that nearly 50% of metastatic melanoma secrete IL-6 into the supernatant. Nevertheless until now the stage dependant effects of IL-6 on melanoma cells are not fully understood. Methods: The secretion of IL-6 by A375, 518A2 human metastatic melanoma cells was compared with WM 35 cells which derive from an early lesion (radial growth phase) and investigated with ELISA. The sensitivity toward statin induced caspase 3 activation was investigated in these cells in the absence and presence of IL-6 or an anti IL-6 receptor antibody (tocilizumab). Apoptosis was also confirmed by FACS analyses for AnnexinV/PI staining and proliferation by cell cycle analysis using PI staining in such treated cells. Phosphorylation of Stat3 and the regulation of pro- (Bax, Bak) and anti-apoptotic proteins (Bcl-2, Bxl-XL) were studied by Western blot. Results: Melanoma cells derived from late stage lesions (A375, 518A2) secrete high amounts of IL-6 in contrast to WM35 cells. IL-6 signalling is intact in A375, 518A2 and WM 35 cells indicated by IL-6 triggered phosphorylation of Stat-3. Most interestingly, the A375 and 518A2 cells show a high sensitivity to simvastatin induced apoptosis with EC50 of 0,52 μM (518A2) and 1,7 μM (A375) in contrast to WM35 cells which are more resistant (EC50 16 μM). Co-treatment with IL-6 leads to an augmentation of the statin induced apoptosis in WM35 cells. Statin induced apoptosis can be mediated by the intrinsic apoptotic pathway which requires the loss of mitochondrial membrane potential. This is often alleviated by a downregulation of antiapoptotic Bcl-2 family members. Interestingly IL-6 treatment led to a marked decrease in the amount of Bcl-2 and Bcl-XL in WM35 cells which may explain the increased activation of apoptosis. Since A375 and 518A2 secrete high amounts of IL-6 we investigated the effects of the anti IL-6 receptor antibody tocilizumab. Conversely interruption of the IL-6 signalling with tocilizumab had no effect on the proliferation of 518A2 and A375 cells. Moreover the simvastatin induced caspase 3 activation was not decreased by blockage of the IL-6 signalling. Conclusion: Taken together our data prove different sensitivities of melanoma cells from various stages to statin induced apoptosis. Moreover, IL-6 facilitates apoptosis in early stage melanoma cells by the down-regulation of anti-apoptotic proteins. Nevertheless, these pro-apoptotic effects of IL-6 are not observed in metastatic melanoma cells indicating a stage specific role of IL-6 in the development and tumorigenesis of melanoma. Citation Format: Christoph Minichsdorfer, Christine Wasinger, Martin Hohenegger. IL-6 primes melanoma cells from early stages to statin induced apoptosis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 336. doi:10.1158/1538-7445.AM2014-336