Abstract 2940: Statin induced apoptosis in human melanoma cells is prevented by inhibition of caspase 2 and translational activity.

Abstract Background: Statins may trigger apoptosis in tumour cells in vitro and, particularly, melanoma cells are susceptible to statin induced apoptosis. Lipophilic statins (e.g. Atorvastatin, Simvastatin) induce strong caspase 3 activation after 48h of treatment, whereas hydrophilic statins (e.g. Pravastatin, Rosuvastatin) do not trigger caspase activation. Recently, we demonstrated the presence of an autocrine amplification loop which increases apoptosis by a caspase 8 dependent pathway after treatment with lipophilic statins (Minichsdorfer and Hohenegger, Br J Ph 2009). It is known that activation of caspase 2 may prime melanoma cells for death receptor induced apoptosis, however, although an association between caspase 2 activation and RhoB upregulation was shown, the significance of this interaction is still not clear. Methods: We investigated the activity of caspase 2, 3 and 8 in A375 and 518A2 human metastatic melanoma cells after statin treatment in the presence and absence of a caspase 2 inhibitor (Z-VDVAD-FMK) or cycloheximide by cleavage of specific fluorescent caspase substrates. Upregulation of RhoB after statin treatment as well as the influence of the co-treatment with the isoprenoids farnesylpyrophosphate (FPP) or geranylgeranylpyrophosphate (GGPP) was studied by Western blot. Results: Exposure of these cells to simvastatin led to increased caspase 2 activation which is abrogated by co-application of the caspase 2 inhibitor Z-VDVAD-FMK. Moreover, treatment with Z-VDVAD-FMK also prevented caspase 8 and caspase 3 activation. We could show that production of an autocrine factor needs an intact translation machinery. Inhibition of translation by co-administration of cycloheximide prevented apoptotic morphological changes as well as caspase 3 and caspase 8 activation in A375 and 518A2 cells. Since caspase 2 may interact with RhoB, we also investigated the effect of statin treatment on RhoB expression and observed an upregulation of RhoB which was inhibited by the addition of cycloheximide in both cell lines. However, isoprenoids were not able to reverse RhoB upregulation or PARP cleavage in 518A2 cells. Conclusion: Overall, our data provide evidence for an important role of caspase 2 in statin induced apoptosis of 2 human metastatic melanoma cell lines. These findings may help to understand the function of caspase 2 in the induction of apoptosis. Moreover, we observed upregulation of RhoB following statin treatment in these cell lines. However, additional experiments are necessary to fully understand the role of RhoB in statin induced apoptosis. Citation Format: Christoph Minichsdorfer, Christine Wasinger, Evelyn Sieczkowski, Atil Bihter, Gerwin Heller, Sabine Zöchbauer-Müller, Martin Hohenegger. Statin induced apoptosis in human melanoma cells is prevented by inhibition of caspase 2 and translational activity. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2940. doi:10.1158/1538-7445.AM2013-2940