INVOLVEMENT OF THE SPHINGOLIPID METABOLISM IN PROSTATE AND BLADDER CANCER MALIGNANCY

Sphingolipids (SLs) are cell membrane amphiphilic components, which reside in the external layer of the plasma membrane (PM), with the hydrophobic moiety, the ceramide (Cer), inserted into the membrane layer and the hydrophilic head group protruding toward the extracellular environment. As membrane components, SLs participate to modulate several cell processes, such as cell growth, motility, differentiation, morphogenesis, cell to matrix interaction and cell to cell communication. From this, it follows that a defect in SL metabolism can obviously lead to a great number of dysfunctions, ranging from neurodegeneration to cancer. During my PhD course, I studied the different faces of SLs in cancer malignancy. In particular, I focused my attention on the involvement of SL as well as of their metabolism in the prostate and bladder cancer malignancy and in their response to the conventional therapies. As well known, prostate cancer (PC) is the most common malignancy and second leading cause of cancer-related death in men. It is generally treated with radiotherapy and androgen ablation even if the onset of resistance is very frequent. Abiraterone is a new promising drug recently approved for the treatment of PC that seems to reduce this drawback inducing cell death also in androgen-resistant PC, nevertheless it mechanism of action is almost unknown. It is nowadays accepted that several pharmacological treatment as well as radiotherapy induce the ceramide-mediated apoptosis through the activation of the PM-associated SL-hydrolyses that generate in situ the formation of pro-apoptotic ceramide. Based on these findings, this study addresses whether these enzymes are a target of abiraterone and of ionizing radiation in human PC. To this purpose, androgen-sensitive and androgen-insensitive PC cell lines were subjected to treatments with abiraterone and/or ionizing radiation and the activities of different PM-associated glycohydrolases as well as the ceramide level were evaluated. Interestingly, all the cell lines tested showed a marked increase in all the PM-associated glycohydrolases as well as in their ceramide content, especially after the combined treatment with abiraterone and ionizing radiation. These data demonstrate the involvement of the glycohydrolases in the mechanisms of abiraterone- and radiation- induced cell death in both androgen sensitive and insensitive PC cells and suggest that these enzymes, able to evocate the production of ceramide at the PM-level, could represent new potential therapeutic targets for prostate cancer. Otherwise, part of my study are related to the involvement of the SL in the bladder cancer cell death induced by the treatment with antagonists of the cannabinoid receptor 2. Bladder cancer (BC) is the most severe malignancy form of the genitourinary tract. Clinically, 75-80% of bladder neoplasms correspond to non-muscle-invasive bladder cancer (NMIBC) at diagnosis. After transurethral resection of the tumor followed by adjuvant chemotherapy, 30 to 50% of patients recur, and more than 15% of those undergo progression to muscle-invasive disease. Identification of novel potential targets to reduce recurrence and prevent disease progression represents a medical challenge for bladder cancer. Among the various putative novel biomarkers or targets recently described for urothelial carcinoma, the endocannabinoid system (ECS), expressed by the genitourinary organs, has recently gained particular attention. The ECS components such as CB1-CB2 receptors, and the endocannabinoid-degrading enzyme fatty acid amide hydrolase (FAAH) are present in the bladder at the epithelial level and play a role in regulating its functions. As recently shown, both clinical and experimental evidence has indicated a possible role of the ECS in modulating cancer proliferation, progression and metastasis in several types of neoplastic diseases, including, prostate and breast cancer. Interestingly, few information are available on the possible role of ECS components in proliferation and metastasis of human urothelial carcinoma, or on the mechanisms underlying progression to the muscle invasive phenotype. In this context, glycosphingolipids (GSL) play an important role. Indeed, aggressive, muscle-invasive BC is characterized by a different expression of the GM3 and Gb3 glycolipids, suggesting that the metabolism of GSL plays a role in controlling cell invasion and motility. Similarly, the known antiproliferative activity of cannabinoids in cancer models is reported to involve changes in GSL metabolism with accumulation of ceramide (Cer) via de novo synthesis and putative deregulation of the Cer/ sphingosine-1-phosphate (S1P) rheostat. Otherwise, the plasma membrane-associated enzymatic hydrolysis of GSL is activated and produces a signaling cascade that may modulate cytoskeletal changes via p-ERM and cell migration via Src. Into this picture though, it’s important also to consider the already reported receptor-independent effects of cannabinoids, which may play an important role in our system. In my study I show a strong associations between the anti-metastatic properties of cannabinoids and GSL metabolism. This finding, together with the in vitro antiproliferative effect, the in vivo efficacy on tumor progression, and the tumor-specific up-regulation of CB2 in primary bladder cancer may play a role in the identification of novel therapeutic and diagnostic targets for treating bladder cancer.