Traditional treatments for prostate cancer rely on surgical resection or radiotherapy for localized cancer and androgen ablation of metastatic cancer. Yet, despite the palliative gains from earlier detection and aggressive treatments, the annual death rate in American men from prostate cancer surpasses 40,000 and increases yearly. As an alternative treatment for cancer, gene therapy-based approaches attempt to increase the immunogenicity of tumor cells while reducing the tumor burden. The HSV thymidine kinase (tk) gene has been the prototype cytocidal gene for tissue-specific cell ablation, targeting surgically inaccessible tumors, or for the safety of gene therapy vectors. Nevertheless, significant hurdles limit human applications, including its specificity for cycling cells, the tk gene's innate immunogenicity, and the fact that ganciclovir is already used as an anti-viral drug. As a novel therapeutic approach, the applicant has developed non-immunogenic conditional death genes, based on """"""""chemically-induced dimerization"""""""" (CID) and Fas-mediated apoptosis. CID technology uses lipid-permeable dimeric drugs to transiently crosslink fusion proteins. The chimeric proteins consist of drug-binding domains derived from endogenous proteins fused to proteins whose function is triggered by cross-linking. Thus, CID enables artificial control of the protein's activity and can work both extracellularly and intracellularly. The Fas receptor is a widely expressed protein that contributes to tissue homeostasis by triggering apoptosis. However, Fas-mediated apoptosis can be blocked by checkpoint genes. The applicant's strategy is to use CID for triggering apoptosis to kill prostate cancer cells through Fas and one of its downstream signaling intermediates, such as Fadd and Yama/CPP32, which may be able to bypass these checkpoints. The applicant proposes three major goals: (i) develop """"""""non-immunogenic"""""""" adenoviral vectors expressing conditional Fas, Fadd and Yama and test their ability to trigger apoptosis in a panel of transformed prostate cell lines in vitro, (ii) test the hypothesis that conditional apoptosis can be used to treat prostate cancer using the TRAMP prostate cancer model developed by Baylor College of Medicine, and (iii) test the hypothesis that apoptotic tumor cells, that are the targets of phagocytic antigen-presenting cells, can elicit a protective anti-tumor immune response. In addition to their potential use as anti-neoplastic agents, these """"""""death switches"""""""" should also have broad applications for developmental studies for increasing the safety of gene therapy vectors.
