In VivoGene Therapy of Cancer withE. coliPurine Nucleoside Phosphorylase

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.

Preclinical evaluation of a prostate-targeted gene-directed enzyme prodrug therapy delivered by ovine atadenovirus

“…[9][10][11][12] In addition, the legitimacy of the overall PNP-GDEPT strategy has been well documented. 17,20,21 In this study where vector was delivered intratumorally, there was no histological evidence of treatment toxicity in liver, spleen, kidney, lung or gut. OAdV623 also successfully delivered PNP/fludarabine-GDEPT to both AS and AI human CaP xenografts producing retarded tumor growth, increased tumor doubling times and host survival.…”

“…27,28 The effective dose of 75 mg/m 2 / day for 5 days used in this work was only three times the dose used in humans and was much lower than that used to treat mice bearing PNP-transfected glioma cell tumors. 21 Although it can bypass pre-existing immunity to human adenoviruses, OAdV does induce an immune response when given i.v. 8 However, intratumoral injection may allow a second administration of vector, albeit with reduced efficiency.…”

Gene therapy for prostate cancer delivered by ovine adenovirus and mediated by purine nucleoside phosphorylase and fludarabine in mouse models

“…The question of the dosage used with GDEPT therefore needs consideration. With GDEPT, the effective dose of fludarabine phosphate given to C57BL/6 mice bearing RM-1 tumors was 600 mg/m 2 /day (Figures 3-5), considerably less than the 1350 mg/m 2 /day for 7 days used by Parker et al, 27 to treat PNP-transfected glioma cell bearing mice. The effective dose that we used for treating nude mice carrying human prostate cancers was 75 mg/m 2 /day ( Figure 6).…”

“…The compounds can be incorporated into both RNA and DNA, killing non-dividing, as well as dividing cells. 27 Moreover, the purine metabolites can diffuse readily both between and within prostate epithelial cells creating an efficient bystander effect. [27][28][29] We have shown that PNP-GDEPT works well against human AI PC-3 prostate cancer cells grown in vitro 30 or subcutaneously (s.c.) in nude mice.…”

“…27 Moreover, the purine metabolites can diffuse readily both between and within prostate epithelial cells creating an efficient bystander effect. [27][28][29] We have shown that PNP-GDEPT works well against human AI PC-3 prostate cancer cells grown in vitro 30 or subcutaneously (s.c.) in nude mice. 18 A recombinant human adenovirus (Ad5) containing the PNP gene controlled by the prostate-specific PSA promoter, together with the prodrug, 6-methyl-9-(2-deoxy-␤-D-erythro-pentofuranosyl) purine (6MEPDR, which is converted by PNP to 6 methylpurine, 6MEP) caused a 75% reduction in PC3 tumor growth, with a complete cure in 25% of mice, and significantly prolonged mouse survival, compared with a control virus that did not contain the active gene cassette.…”