928. Reversal of PPC1 Prostate Cancer Cells Radioresistance by Degradation of Acid Ceramidase Using the Lysosomotropic Drug LCL385

Prostate cancer is the most common malignancy in USA males and one of the most common causes of death from cancer in men. Resistance of prostate cancer cells to radiation therapy is still a major concern. This radio-resistance may be due to defects in the apoptotic signaling pathways. In addition to their important role as structural components of cell membranes, sphingolipids have been lately shown to be important signaling molecules with crucial roles in cancer cells apoptosis. At the center of sphingolipid metabolism is the tumor suppressor lipid ceramide. Ceramide has many cellular signaling functions the most important of which is the pro-apoptotic function. Acid ceramidase (AC) is one of the enzymes that metabolize ceramide and hence it is believed to mediate resistance to apoptosis and cell death. In this study, we found that radiation of PPC1 prostate cancer cells, up regulates AC in a time dependent manner. This up regulation started as early as one hour after radiation and persisted up to 72 hours. Thus, AC up regulation certainly contributes to the mechanisms by which these cell lines gain resistance to radiation induced apoptosis. We are also investigating ceramide level following radiation as it is expected to go down in parallel with AC up regulation. Using these important data we used the MTS assay to investigate the effect of the lysosomotropic agent LCL385 -a drug that is known to degrade AC in a dose and time dependent manner- as a pretreatment to and we compared the results with those after using LCL alone and radiation alone. We found that radiation alone failed to induce apoptosis in these cell lines using as high as 30 Gy and for a period up to 72 hours following radiation, however using LCL385 as a pre-treatment with radiation ,induced apoptosis (up to 55%) using as low as 5Gy and after a period of 48 hours following radiation. This represents a new method of sensitizing ppc1 prostate cancer cells through an acid ceramidase inhibition mechanism.