Objective: Recent advances in diagnostics, staging, and therapy for pancreatic cancer have not resulted in significant improvements in long-term survival, and development of new approaches is particularly urgent. The use of prodrug-activating genes is a possible approach for cancer gene therapy. The aim of this study was to evaluate the efficacy of Escherichia coli purine nucleoside phosphorylase (ePNP) on pancreatic tumors. ePNP activates the prodrug 6-methylpurine deoxyribose (MePdR) into methyl purine (MeP), which is highly toxic to dividing and nondividing cells.
Methods: A recombinant pCAG-ePNP vector was constructed and used to establish pancreatic cancer cells expressing constitutively ePNP (ePNP+). The ePNP/MePdR system effects were tested in vitro on HA-RPC (rat) and BxPC3 (human) pancreatic cancer cell lines and then in vivo on tumors established in nude mice with BxPC3 ePNP+ cells.
Results: MePdR treatment of ePNP+ tumor cells induced cytotoxic and antiproliferative effects in a concentration-dependent manner with a 100% cell death since 5 x 10 mol/L. Bystander effect was strong in vitro as more than 50% of tumor cells were killed by MePdR with only 1%-2% of ePNP+ cells. In vivo, tumor growth was completely abolished with a prodrug treatment initiated 2 days after tumor cell inoculation, and mice remained tumor free. In addition, even if MePdR treatment was applied to large tumors, tumors significantly regressed.
Conclusion: These preliminary results support the therapeutic potential of the MePdR/ePNP system, which induces a highly cytotoxic effect with a potent bystander effect on pancreatic tumors.