The effects of ceramide on these apoptosis mediators are apparently cell type or cellular context dependent since LCL85 only alters the expression level of Bcl xL in human colon and breast cancer cells. Here, we identified xIAP and cIAP1 as targets of the kinase inhibitor 17-AAG ceramide signaling pathways in both metastatic human colon and breast cancer cells. We observed that LCL85 effectively decreased cIAP1 and xIAP protein levels in metastatic human colon and breast cancer cells. Consistent with the decreased xIAP1 and cIAP1 protein levels, metastatic human colon carcinoma cells exhibited increased sensitivity to FasL induced apop tosis. Furthermore, treatment of metastatic human colon carcinoma cells with cIAP1 and xIAP specific inhibitor BV6 also significantly increased tumor cell sensitivity to FasL induced apoptosis.
Inhibitors,Modulators,Libraries Therefore, our data suggest that xIAP1 and cIAP1 proteins are responsible, at least in part, for the apoptosis resistant phenotype in metastatic human colon and breast cancers, and LCL85 overcomes metastatic human colon and breast cancer cell resistance to Fas mediated apoptosis at least partially through indu cing proteasomal degradation of Inhibitors,Modulators,Libraries xIAP and cIAP1 proteins. It has been well documented that Smac mimetic BV6 specifically targets cIAP1 and cIAP2 proteins to induce apoptosis through activating the TNF signaling pathway. However, it has also been shown that xIAP, rather than cIAP1 and cIAP2, is the critical target of BV6 in Fas mediated apoptosis. Strikingly, we observed that LCL85 also sensitizes tumor cells to Fas mediated apoptosis through inducing proteasomal degradation of xIAP.
LCL85 treatment increased endogenous C16 cer amide level and exogenous C16 ceramide Inhibitors,Modulators,Libraries is effective in sensitizing the apoptotic resistant metastatic human colon carcinoma cells to Fas mediated apoptosis. Therefore, it is Inhibitors,Modulators,Libraries possible that LCL85 sensitizes tumor cells to Fas mediated apoptosis at least in part through inducing C16 ceramide accumulation, resulting in ceramide Inhibitors,Modulators,Libraries mediated xIAP and cIAP1 proteasomal degradation. However, the molecular mechanisms underlying the crosstalk network between ceramide analog, C16 ceramide and IAP proteins remain to be elucidated. Ceramide analog mediated direct cytotoxicity often depends on administering a high dose of the agent. In this study, LCL85 exhibited potent anti tumor cytotoxicity, suggesting that LCL85 is potentially an effective therapeutic agent in cancer therapy.
However, LCL85 also phase 3 exhibited toxicity in a dose dependent manner. Therefore, LCL85 might also be toxic if used in high doses. Interestingly, we demonstrated that a sublethal dose of LCL85 is not cytotoxic but effectively sensitizes metastatic human colon carcinoma cells to FasL induced apoptosis in vitro. This observation is significant since a sublethal dose of LCL85 might be safe and yet an effective sensitizer in FasL CTL based cancer immunotherapy.