Suicide Gene/Prodrug Therapy for Pancreatic Adenocarcinoma by E. Coli Purine Nucleoside Phosphorylase and 6-Methylpurine 2′-deoxyriboside

Abstract

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. 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. 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. 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.