PARENT SESSION
1:30 PM to 2:30 PM
Monday, April 22, 2002
Poster Session 4 Gene Therapy
Room: Nevada 4-5
(MP04-37) Tumor-specific drug delivery using non-pathogenic bacteria: an alternative to gene therapy approaches.
Theys, Jan*,1,2,3, Landuyt, Willy2, Nuyts, Sandra2, Wouters, Brad1, Anne, Jozef3, Lambin, Philippe1,2, 1 Laboratory of Experimental Radiation Oncology, Maastricht, The Netherlands2 Laboratory of Experimental Radiobiology and Experimental Oncology, Leuven, Belgium3 Laboratory of Bacteriology, Leuven, Belgium
ABSTRACT-
The presence of hypoxia in solid tumors often limits the efficacy of conventional treatment modalities. However, the unique physiology of human tumors that gives rise to hypoxia also offers the potential for therapeutic exploitation. We are developing and testing a tumor specific gene therapy delivery system using anaerobic bacteria. Systemically administered spores of non-pathogenic Clostridium bacteria specifically germinate into metabolically active vegetative cells in the hypoxic/necrotic regions of solid tumors. This sytem has proven to be tumor-specific and safe. We have genetically engineered clostridia to express and secrete the cytokine tumor necrosis factor 
(TNFa) or the prodrug converting E. coli cytosine deaminase enzyme (CDase). Expression and secretion of TNF in transformed clostridia was shown by Western blot analysis and biological activity was detected in a bioassay using WEH164 cells. CDase activity of engineered clostridia was demonstrated by the conversion of 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU) using thin layer chromatography. Administration of these recombinant strains to rhabdomyosarcoma bearing rats resulted in the presence of active therapeutic proteins at the tumor site. Moreover, following administration of the vascular targeting agent combretastatin A-4 phosphate, significantly increased levels of CDase were detected at the tumor site as a consequence of increased tumor necrosis and subsequent improved colonization of Clostridium. We are currently investigating anti-tumoral effects in mice bearing HT29 colorectal tumors. Preliminary results using CDase recombinant clostridia combined with continuous 5-FC administration, are encouraging. Based on these data and supported by its selective colonization pattern and safety, we believe that the clostridial-based gene transfer system has significant potential for application in anti-cancer therapies.
KEYWORDS: Clostridium, hypoxia, gene delivery, suicide gene