As they grow in volume many tumors, including pancreatic and colon cancers, construct poorly vascularized and oxygen-deficient (hypoxic) areas that restrict the access by therapeutic agents and limit the efficacy of currently used anti-cancer modalities. However, the presence of hypoxia also offers the potential for anaerobic bacterial colonization that can lead to tumor destruction. One such anerobic bacterium is Clostridium perfringens (Cp), which contains a major toxin gene that encodes phospholipase C (plc). A plc-deleted strain of Cp (Cp/plc-) has been constructed in our laboratory and shown, after intravenous administration, to colonize and induce massive necrosis in solid tumors in mice. Unfortunately Cp/plc- retains some tolerance to oxygen that enables it to grow in normal tissues at a much reduced rate, and tumor-bearing mice treated with Cp/plc- at the effective doses also exhibited systemic toxicity. We hypothesize that Cp/plc- can be genetically modified to reduce substantially its oxygen tolerance, thereby creating sub-strains that will lead to tumor destruction without toxicity to normal tissues. We propose to delete the superoxide dismutase (sod) gene in a luciferase-expressing strain of Cp/plc-/LUC+ (Cp/plc-/sod-/LUC+). Immune- competent mice with pre-established syngeneic colorectal and pancreatic cancers in the liver will be treated by intravenous administration of Cp/plc-/sod-. Dose response curve and long-term survival at the maximal tolerated dose will be determined. Bacterial biodistribution and intratumoral growth will be determined as a function of time by repeated non-invasive whole-body imaging using luciferrin. Tumor responses in the treated animals will be evaluated by histological examination. Toxicity endpoints will include CBC, blood chemistries, serum proinflammatory cytokine levels and history of major organs. If necessary, additional oxygen tolerance genes can be deleted from Cp/plc-/sod- to further reduce toxicity. We hypothesize that these oxygen-intolerant mutant bacterial sub-strains can be safely applied in tumor-bearing animals, which will selectively localize to, germinate and grow in, and destroy tumors in hypoxic regions. Application of anaerobic bacterial-based vectors is a promising strategy for the development of an effective therapeutic agent that can be administered systemically to treat disseminated solid tumors with hypoxia, and may lead to clinical translational studies in patients with metastatic colorectal and/or pancreatic cancers in the future. ? ?
| Li, Zhiyu; Fallon, John; Mandeli, John et al. (2009) The oncopathic potency of Clostridium perfringens is independent of its alpha-toxin gene. Hum Gene Ther 20:751-8 |
| Li, Zhiyu; Fallon, John; Mandeli, John et al. (2008) A genetically enhanced anaerobic bacterium for oncopathic therapy of pancreatic cancer. J Natl Cancer Inst 100:1389-400 |
