Thymidine kinase-deleted vaccinia virus expressing purine nucleoside phosphorylase as a vector for tumor-directed gene therapy.
Tumor-directed gene therapy faces many obstacles. Lack of tissue targeting and low in vivo transduction efficiency represent some of the limitations for a successful therapeutic outcome. A thymidine kinase-deleted mutant vaccinia virus has been shown in marker studies to replicate selectively in tumor tissue in animal models. Purine nucleoside phosphorylase (PNP), from E. coli, converts the nontoxic prodrug 6-methylpurine deoxyriboside (6-MPDR) to the toxic purine 6-methylpurine. In this study, we investigated the cytotoxic properties of PNP, expressed by an optimized synthetic early/late promoter in a vaccinia virus (vMPPNP). In vitro cytotoxicity of psoralen-inactivated vMPPNP (1 microg of psoralen, 4 min of LWUV [365 nm]) at the maximum tolerated dose (MTD) of 6-MPDR (80 microM) reduced cell viability by day 3 to 1.7%. At an MOI of 0.002, replication-competent vMPPNP and 6-MPDR (80 microM) caused reduction of cell viability to 19.8% within 4 days. Furthermore, there was complete abrogation of viral replication after intracellular conversion of prodrug into the active toxin. The potency of such a system was similar among all histologies tested. Finally, the cytotoxic efficacy has been shown to be more rapid and complete than that of cytosine deaminase (CD), a more established enzyme/prodrug system. When virus was delivered intraperitoneally into athymic mice with hepatic metastases, followed by administration of prodrug, there was a significant prolongation of survival and a 30% cure rate. In summary, owing to its tumor-targeting capabilities, high transduction efficiency, and high gene expression, a vaccinia virus expressing PNP could prove to be a potent and valuable vector for tumor-targeted gene therapy.
Puhlmann
M
M
Surgery Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Gnant
M
M
Brown
C K
CK
Alexander
H R
HR
Bartlett
D L
DL
D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D011564:Furocoumarins / Q000494:pharmacology; D017353:Gene Deletion; D015316:Genetic Therapy; D005822:Genetic Vectors; D006801:Humans; D008114:Liver Neoplasms, Experimental / Q000556:secondary / Q000628:therapy; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000473:pathology / Q000628:therapy*; D011683:Purine-Nucleoside Phosphorylase / Q000235:genetics*; D013937:Thymidine Kinase / Q000235:genetics*; D014407:Tumor Cells, Cultured; D014616:Vaccinia virus / Q000201:enzymology / Q000235:genetics* / Q000502:physiology; D014779:Virus Replication / Q000187:drug effects
D011564:Furocoumarins; D011683:Purine-Nucleoside Phosphorylase; D013937:Thymidine Kinase