title: In vivo enhancement of herpes simplex virus thymidine kinase/ganciclovir cancer gene therapy with polyamine biosynthesis inhibition.
abstract: We have earlier demonstrated that inhibition of polyamine biosynthesis with difluoromethylornithine (DFMO) can be used to enhance the cytotoxicity of herpes simplex virus thymidine kinase/ganciclovir (HSV-TK/GCV) gene therapy in different tumor cell lines. Here, the utility of this treatment combination was tested in vivo in a nude mouse tumor model. First, the effect of DFMO was verified by treating mice bearing subcutaneous 9L rat glioma tumors with 2% DFMO in drinking water. The drug treatment induced almost complete suppression of ornithine decarboxylase activity, and as a result, a strong decrease in intratumoral putrescine and spermidine concentrations, which were normalized 4 days after drug removal. Consequently, the tumors displayed a significant reduction in the proliferation activity that was increased to 20% higher than the normal level at day 4 and returned to normal level 7 days after DFMO removal. Next, 9L tumors with 30% of TK-GFP fusion gene positive cells were induced and the animals were given DFMO and GCV in 2 treatment schemes, with the drug administration periods overlapping either 5 or 2 days. The analysis of tumor size at the end of the treatment revealed that DFMO can enhance HSV-TK/GCV cytotoxicity when the overlap between DFMO and GCV was 5 days, but the result was not significant. However, the 2-day overlap scheme yielded a significantly (p < 0.05, ANOVA) enhanced antitumor effect. In conclusion, the data here confirms that a novel combination of 2 clinically relevant treatment modalities, polyamine deprivation and HSV-TK/GCV suicide gene therapy, can be used synergistically in vivo.
authors.affiliation: Department of Biotechnology and Molecular Medicine, A. I. Virtanen Institute for Molecular Sciences, University of Kuopio, Kuopio, Finland.
authors.forename: Tiina
authors.initials: T
authors.lastname: Wahlfors
authors.forename: Tanja
authors.initials: T
authors.lastname: Hakkarainen
authors.forename: Juhani
authors.initials: J
authors.lastname: Jänne
authors.forename: Leena
authors.initials: L
authors.lastname: Alhonen
authors.forename: Jarmo
authors.initials: J
authors.lastname: Wahlfors
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001932:Brain Neoplasms / Q000235:genetics / Q000628:therapy*; D000518:Eflornithine / Q000494:pharmacology*; D005260:Female; D015774:Ganciclovir / Q000627:therapeutic use*; D041722:Genes, Transgenic, Suicide; D015316:Genetic Therapy; D005910:Glioma / Q000235:genetics / Q000628:therapy*; D051379:Mice; D008819:Mice, Nude; D011073:Polyamines / Q000378:metabolism; D018139:Simplexvirus / Q000472:pathogenicity*; D013937:Thymidine Kinase / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D011073:Polyamines; D013937:Thymidine Kinase; D015774:Ganciclovir; D000518:Eflornithine