A genetically enhanced anaerobic bacterium for oncopathic therapy of pancreatic cancer

Abstract

Background: A major obstacle in treatment of solid tumors is the inefficient delivery of therapeutic agents to the hypoxic cores. Hypoxia offers the potential for anaerobic bacteria colonization and tumor destruction by the bacteria, and dormant spores of wild-type Clostridium perfringens (Cp) germinate and proliferate within the hypoxic cores of pancreatic tumors in mice. However, the oncopathic effects of Cp were limited by host inflammatory responses and by Cp's residual tolerance to oxygen, which caused toxic effects in animals. Methods: Recombinant Cp strains in which superoxide dismutase, a major oxygen tolerance gene, was deleted (Cp/sod-) were constructed to enhance its selective growth in tumors. In addition, Panton-Valentine Leukocidin (PVL), an inflammation-suppressing gene from Staphylococcus aureus, was inserted into the Cp/sod- genome to enhance its oncopathic potency. The ability of the recombinant Cp strains to kill tumors was investigated in C57/BL6 mice bearing murine PANC02 tumors. Systemic and organ toxic effects were assessed by monitoring serum chemistries and histopathological examination. Statistical tests were two-sided. Results: Cp/sod- showed reduced toxic effects compared with wild-type Cp when spores were administered intravenously into PANC02 tumor-bearing mice. Mice treated with Cp/sod-/PVL spores demonstrated a reduction in neutrophils and macrophages in tumors, logarithmically elevated growth of intratumoral bacteria, enhanced tumor necrosis, and substantially prolonged survival without apparent systemic and organ toxic effects, compared with mice treated with both wild-type Cp and Cp/sod- spores. Accordingly, 47% of Cp/sod-/PVL-treated mice (n = 15) achieved tumor-free survival for over 120 days, whereas all mice treated with Cp/sod- or phosphate-buffered saline (n = 10 per group) died within 50 days. The median survival for Cp/sod-/PVL-treated mice was 77 days (95% confidence interval [CI] = 45 to 120 days) and for Cp/sod --treated mice was 30 days (95% CI = 23 to 36 days; P