Purine nucleoside phosphorylase and fludarabine phosphate gene‐directed enzyme prodrug therapy suppresses primary tumour growth and pseudo‐metastases in a mouse model of prostate cancer

Abstract

Gene-directed enzyme prodrug therapy based on the E. coli purine nucleoside phosphorylase (PNP) gene produces efficient tumour cell killing. PNP converts adenosine analogs into toxic metabolites that diffuse across cell membranes to kill neighbouring untransduced cells (PNP-GDEPT). Interference with DNA, RNA and protein synthesis kills dividing and non-dividing cells, an important consideration for slow-growing prostate tumours. This study examined the impact of administering PNP-GDEPT into orthotopically grown RM1 prostate cancers (PCas) on the growth of lung pseudo-metastases of immunocompetent mice. C57BL/6 mice bearing orthotopic RM1 PCas received a single intraprostatic injection of OAdV220 (10(10) particles), a recombinant ovine atadenovirus containing the PNP gene controlled by the Rous Sarcoma virus promoter, followed by fludarabine phosphate (approximately 600 mg/m(2)/day) administered intraperitoneally (ip) once daily for 5 days. Pseudo-metastases were induced 2 days after intraprostatic vector administration by tail-vein injection of untransduced RM1 cells. Mice given PNP-GDEPT showed a significant reduction both in prostate volume (approximately 50%) and in lung colony counts (approximately 60%). Apoptosis was increased two-fold in GDEPT-treated prostates compared with controls (P < 0.01), but was absent in the lungs. Staining for proliferating cell nuclear antigen (PCNA) indicated that proliferation of both RM1 prostate tumours (P < 0.01) and lung colonies (P < 0.01) was significantly suppressed after GDEPT. Although prostate tumour immune cell infiltration did not differ significantly between treatments, immunostaining for Thy-1.2 (CD90) showed that GDEPT promoted Thy-1.2(+) cell infiltration into the prostate tumour site. This study showed that a single course of PNP-GDEPT significantly suppressed local PCa growth and reduced lung colony formation in the aggressive RM1 tumour model.

Mesenchymal stromal cells retrovirally transduced with prodrug-converting genes are suitable vehicles for cancer gene therapy

“…Mice given PNP-GDEPT showed a significant reduction both in prostate volume and in lung colony counts. Apoptosis was increased two-fold in treated prostates compared to controls (Martiniello-Wilks et al, 2004). Thus preclinical studies using animal models have demonstrated that PNP anticancer gene therapy is a promising approach for the treatment of solid tumors.…”

Molecular Chemotherapy and Chemotherapy: A New Front against Late-Stage Hormone-Refractory Prostate Cancer

“…RM1 cells express androgen receptors and yet display androgen independence (the most aggressive CRPC phenotype encountered in humans), forming aggressive tumors. The RM1 model has been successfully used in preclinical studies to evaluate different anticancer therapies against local and metastatic PCs (9,11,18,20,24). (ii) Human PC-3 cells that exhibit several characteristics of late-stage CRPC and provide a clinically relevant model to assess antitumor responses of various therapies (25,26).…”

“…In fact, PNP-GDEPT efficacy against late-stage PC has been previously shown in our laboratory in xenogeneic and syngeneic mouse models of local and metastatic CRPC (human PC-3 and murine RM1; refs. [9][10][11], and significantly, PNP-GDEPT prolonged survival rate of mice with transgenic adenocarcinoma of the prostate (TRAMP; ref. 12).…”

“…Both PNP-GDEPT and docetaxel treatments may lead to dysregulated immune responses, as reflected in the involvement of immune cells (9)(10)(11)(12), and/or altered cytokine profiles in docetaxel-treated patients (14). In particular, fluctuations in T-helper type (Th) 1/Th2 cytokines have been successfully exploited for noninvasive assessment of cancer progression and patient response in the clinical setting (15,16).…”

Development of gene therapy in association with clinically used cytotoxic deoxynucleoside analogues

“…48 Both prodrug-activating systems induce apoptosis in Transduction of PNP gene followed by treatment with nucleoside analogues has been studied in vivo on bladder tumors, pancreatic adenocarcinomas, gliomas, ovarian or prostate tumors and showed different levels of growth inhibition. 40,44,[49][50][51][52][53][54][55][56] To increase the effect obtained with this gene-therapy approach by using new genes and new drugs, a study based on crystallographic and computer modeling of E. coli PNP, was performed. The mutated protein (M64V) had a more than 100-fold increased enzymatic efficiency (kcat/Km) toward the nontoxic 9-(6-deoxy-a-L-talofuranosyl)-6-methylpurine as compared to the wt protein.…”