Potentials and limitations of adenovirus-p53 gene therapy for brain tumors

We investigated the antineoplastic potentials of recombinant adenovirus containing wild-type p53 cDNA (Ad5CMV-p53) for malignant gliomas. In four human glioma cell lines (U-251 and LG expressing endogenous mutant p53, and U-87 and EFC-2 expressing wild-type p53) and two rat glioma cell lines (9L and C6, each expressing mutant and wild-type p53), gene transfer efficiency determined by X-gal staining and Western blotting was varied (10-99% at 10-500 multiplicity of infection, MOI). Growth inhibitory effect was drastic (>90% at 100 MOI) in U-251 cells and only moderate or minimal in other cell lines harboring wild-type p53 or low gene transfer efficiency. Ex vivo transduction of U-251 cells with Ad5CMV-p53 suppressed the in vivo tumorigenicity of the cells. Histopathologic examination for Ad5CMV-p53 toxicity to rat brains showed inflammatory reactions in half of the tested brains at 10(8) MOI. U-251 cells were inoculated intracerebrally in nude mice and injected Ad5CMV-p53 into the tumor, in which neither the tumor suppression nor the survival benefit was observed. In conclusion, heterogeneity of the cellular subpopulations of malignant glioma in p53 status, variable and insufficient gene delivery to tumor, and adenoviral toxicity to brain at higher doses may be limiting factors to be solved in developing adenovirus-p53 gene therapy for malignant gliomas.

Potentials and limitations of adenovirus-p53 gene therapy for brain tumors

We investigated the antineoplastic potentials of recombinant adenovirus containing wild-type p53 cDNA (Ad5CMV-p53) for malignant gliomas. In four human glioma cell lines (U-251 and LG expressing endogenous mutant p53, and U-87 and EFC-2 expressing wild-type p53) and two rat glioma cell lines (9L and C6, each expressing mutant and wild-type p53), gene transfer efficiency determined by X-gal staining and Western blotting was varied (10-99% at 10-500 multiplicity of infection, MOI). Growth inhibitory effect was drastic (>90% at 100 MOI) in U-251 cells and only moderate or minimal in other cell lines harboring wild-type p53 or low gene transfer efficiency. Ex vivo transduction of U-251 cells with Ad5CMV-p53 suppressed the in vivo tumorigenicity of the cells. Histopathologic examination for Ad5CMV-p53 toxicity to rat brains showed inflammatory reactions in half of the tested brains at 10(8) MOI. U-251 cells were inoculated intracerebrally in nude mice and injected Ad5CMV-p53 into the tumor, in which neither the tumor suppression nor the survival benefit was observed. In conclusion, heterogeneity of the cellular subpopulations of malignant glioma in p53 status, variable and insufficient gene delivery to tumor, and adenoviral toxicity to brain at higher doses may be limiting factors to be solved in developing adenovirus-p53 gene therapy for malignant gliomas.

Gene Therapy of Brain Tumors:Effects of Adenovirus-mediated Wild Type p53 Gene Transfer in Human Glioma Cells

The p53 tumor suppressor gene is one of the genes with greatest therapeutic potential for cancer treatment and its growth inhibitory mechanism is thought to be mediated through the activation of its downstream mediator, WAF1/Clip1. In this study, we evaluated the effect of the replication-defective recombinant adenovirus expressing wild-type p53 gene(Ad5CMV-p53) in human glioma cell lines(U-251, LG) harboring mutant-type p53. beta-galactosidase histochemistry revealed that 90% of the U-251 and 42% the of LG cells are infected with the adenovirus at a multiplicity of infection(MOI) of 25 plaque-forming units(PFU)/cell. Immunoblot analyses showed that endogenous p53 protein is expressed at a high level, and significant exogenous p53 protein expression and WAF1/Clip 1 induction peaked on day 1 and day 3 after Ad5CMV-p53 treatment. Introduction of Ad5CMV-p53 inhibited the cell rowth of U-251(85% inhibition) and LG cells(36% inhibition), and influenced cell morphology. The optimal dose of Ad5CMV-p53 for the tumor cel ls growth inhibition was MOI of 10-40 PFU/cell. These results suggest that Ad5CMV-p53 infects human glioma cells and transduces the p53 gene with high efficiency, and could be further developed for the gene therapy of human gliomas.