Ming X. Wei

Effects on brain tumor cell proliferation by an adenovirus vector that bears the Interleukin-4 gene

A recombinant adenovirus vector bearing the IL-4 gene (AD-IL-4) was used to infect rat glioma C6 cells in culture at multiplicity of infections (MOI) from 50 to 1800. C6 cell proliferation was not altered significantly by adenoviral infection. However, IL-4 production increased in a dose-dependent manner. To ascertain effects on in vivo cell proliferation, a subcutaneous tumor model was used. Rat C6 glioma cells alone or C6 mixed with the control virus bearing the LacZ gene (Ad-LacZ) produced tumors that measured an average of approximately 3000 mm3 35 days after implantation. In contrast, C6 cells mixed with Ad-IL-4 produced significant inhibition of tumor growth (P=0.035 compared to C6 tumor; P=0.023 compared to C6+Ad-LacZ tumor. Students ttest). IL-4 levels in mice serum were measured by ELISA and reached a peak of approximately 700 pg/ml at 14 days. These preliminary results showed that adenovirus-mediated delivery of the IL-4 gene may result in a significant inhibition of rat C6 cell tumor growth. Further studies will be necessary to refine this anti-tumor effect for as a potential therapy for cancer.

Virus Vector-Mediated Transfer of Drug-Sensitivity Genes for Experimental Brain Tumor Therapy

Publisher Summary This chapter summarizes the gene therapy strategies that employ virus vectors to deliver drug-sensitivity genes into brain tumor cells. Drug-sensitivity genes encode enzymes that activate prodrugs into their toxic metabolites. In order to transfer these genes into tumor cells in vivo , modified viruses and other agents can be employed as vectors. Three types of viral vectors have been reported as efficient vectors when applied to experimental brain tumors: retrovirus, herpes virus, and adenovirus. One major difference among retrovirus, herpes simplex virus, and adenovirus vectors is that with retroviruses, gene expression requires integration into the host cell chromosome and this integration occurs only in dividing cells. This property provides for selectivity in the delivery of drug-sensitivity genes into dividing tumor cells since most endogenous cells in the brain are postmitotic. Issues of safety have been met by genetically modifying and designing Moloney murine leukemia virus-based (MoMLV) vectors and mouse fibroblast packaging cells (ψ CRE/CRIP) to minimize the risk of recombination after infection, which could result in regeneration of pathogenic replication-competent retrovirus. Replication-defective adenovirus vectors have also been employed to deliver the reporter gene, LacZ, into endogenous neural cells, as well as into tumor . This vector can be grown to high titers and does not integrate into the host cell genome. In case of herpes virus, two types have been developed for gene delivery to the central nervous system: replication-defective recombinant viruses and plasmid-derived amplicons. Several types of genes have been shown to possess antitumor effectiveness: (1) drug-enhancing genes encode enzymes, (2) immune-response enhancer genes such as such as interleukin-2, (3) tumor-suppressor genes such as p53, and (4) antisense RNAs such as that to insulin-like growth factor I. Three other gene encoding enzymes that convert prodrugs to drugs are HSVtk Gene, Escherichia coli Cytosine Deaminase (CD) Gene and Escherichia coli GPT Gene, and Cytochrome P450 2B1 Gene.