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In vivo gene therapy of cancer with E. coli purine nucleoside phosphorylase
W B Parker1, S A King, P W Allan
1Southern Research Institute, Birmingham, AL 35205, USA.
Abstract:
We have developed a new strategy for the gene therapy of cancer based on the activation of purine nucleoside analogs by transduced E. coli purine nucleoside phosphorylase (PNP, E.C. 2.4.2.1). The approach is designed to generate antimetabolites intracellularly that would be too toxic for systemic administration. To determine whether this strategy could be used to kill tumor cells without host toxicity, nude mice bearing human malignant D54MG glioma tumors expressing E. coli PNP (D54-PNP) were treated with either 6-methylpurine-2'-deoxyriboside (MeP-dR) or arabinofuranosyl-2-fluoroadenine monophosphate (F-araAMP, fludarabine, a precursor of F-araA). Both prodrugs exhibited significant antitumor activity against established D54-PNP tumors at doses that produced no discernible systemic toxicity. Significantly, MeP-dR was curative against this slow growing solid tumor after only 3 doses. The antitumor effects showed a dose dependence on both the amount of prodrug given and the level of E. coli PNP expression within tumor xenografts. These results indicated that a strategy using E. coli PNP to create highly toxic, membrane permeant compounds that kill both replicating and nonreplicating cells is feasible in vivo, further supporting development of this cancer gene therapy approach.
Insights
This cancer gene therapy uses E. coli purine nucleoside phosphorylase (PNP) to activate prodrugs, creating toxic antimetabolites within tumor cells. This approach effectively eliminated tumors with no systemic toxicity, showing promise for cancer treatment.
Area of Science:
- Oncology
- Molecular Biology
- Gene Therapy
Background:
- Cancer gene therapy aims to selectively target and eliminate tumor cells.
- Purine nucleoside phosphorylase (PNP) from E. coli can activate specific prodrugs.
Purpose of the Study:
- To evaluate a novel cancer gene therapy strategy using E. coli PNP to activate purine nucleoside analogs intracellularly.
- To determine the efficacy and toxicity of this approach in a preclinical model.
Main Methods:
- Developed a gene therapy strategy involving transduction of human D54MG glioma tumors with E. coli PNP.
- Treated tumor-bearing mice with prodrugs: 6-methylpurine-2'-deoxyriboside (MeP-dR) or fludarabine (F-araA precursor).
- Assessed antitumor activity and systemic toxicity in vivo.
Main Results:
- Both MeP-dR and F-araA prodrugs demonstrated significant antitumor activity against D54-PNP tumors.
- Effective doses showed no discernible systemic toxicity in the host.
- MeP-dR achieved curative results in 3 doses for solid tumors.
- Antitumor effects correlated with prodrug dose and E. coli PNP expression levels.
Conclusions:
- E. coli PNP-mediated activation of prodrugs is a feasible in vivo strategy for cancer gene therapy.
- This method generates highly toxic compounds intracellularly, targeting both replicating and non-replicating tumor cells.
- The approach shows potential for developing effective and non-toxic cancer treatments.