Intratumoral administration of an adenovirus expressing a kinase dead form of ErbB-2 inhibits tumor growth

Recombinant AAV-mediated HSVtk gene transfer with direct intratumoral injections and Tet-On regulation for implanted human breast cancer

BACKGROUND

HSVtk/ganciclovir (GCV) gene therapy has been extensively studied in tumors and relies largely on the gene expression of HSVtk. Most studies, however, have failed to demonstrate any significant benefit of a controlled gene expression strategy in cancer treatment. The Tet-On system is commonly used to regulate gene expression following Dox induction. We have evaluated the antitumor effect of HSVtk/ganciclovir gene therapy under Tet-On regulation by means of adeno-associated virus-2 (AAV-2)-mediated HSVtk gene transfer with direct intratumoral injections in mice bearing breast cancer tumors.

METHODS

Recombinant adeno-associated virus-2 (rAAV) was constructed and transduced into MCF-7 cell line. GCV treatment to the rAAV infected MCF-7 cells was performed by MTT assay under the doxycycline (Dox) induction or without Dox induction at a vp (viral particle) number of > or =10(4)/cell. The virus was administered intratumorally to nude mice that had also received GCV intraperitoneally. The antitumor effects were evaluated by measuring tumor regression and histological analysis.

RESULTS

We have demonstrated that GCV treatment to the infected MCF-7 cells under the Dox induction was of more inhibited effects than those without Dox induction at > or =10(4) vp/cell. In ex vivo experiments, tumor growth of BALB/C nude mice breast cancer was retarded after rAAV-2/HSVtk/Tet-On was injected into the tumors under the Dox induction. Infiltrating cells were also observed in tumors after Dox induction followed by GCV treatment and cells were profoundly damaged. The expression of HSVtk gene in MCF-7 cells and BALB/C nude mice tumors was up-regulated by Tet-On under Dox induction with reverse transcription-PCR (RT-PCR) analysis.

CONCLUSION

The antitumor effect of rAAV-mediated HSVtk/GCV gene therapy under the Dox induction with direct intratumoral injections may be a useful treatment for breast cancer and other solid tumors.

Recombinant Adenovirus Vaccines Can Successfully Elicit CD8+ T Cell Immunity under Conditions of Extreme Leukopenia

We have examined the efficacy of vaccination with recombinant adenovirus under conditions of extreme leukopenia in lethally irradiated mice reconstituted with autologous bone marrow. The expansion of antigen-specific CD8(+) T cells following immunization of lethally irradiated hosts paralleled the recovery of total CD8(+) T cells. Surprisingly, the numbers of antigen-specific CD8(+) T cells in lethally irradiated mice beyond 6 weeks postimmunization were comparable to the numbers found in nonirradiated controls. CD8(+) T cells elicited in the lethally irradiated hosts were functionally indistinguishable from those elicited in normal hosts. Antigen expression and presentation persisted for a longer period of time in the draining lymph nodes of irradiated mice compared to those of nonirradiated animals, suggesting that antigen presentation mechanisms were intact during the reconstitution period. Experiments employing allogeneic bone marrow demonstrated that radioresistant host antigen-presenting cells were responsible for antigen presentation during the process of immune reconstitution. These results demonstrate clear compatibility of adenovirus vaccines and cytotoxic therapy. Furthermore, these observations provide novel insights into the mechanisms of CD8(+) T cell activation following adenovirus immunization.

EpCAM is overexpressed in breast cancer and is a potential target for breast cancer gene therapy

EpCAM (epithelial cell adhesion molecule) is a cell surface molecule that is known to be highly expressed in colon and other epithelial carcinomas. EpCAM is involved in cell-to-cell adhesion and has been the target of antibody therapy in several clinical trials. To assess the value of EpCAM as a novel target for breast cancer gene therapy, we performed real-time reverse transcription-PCR to quantify the level of EpCAM mRNA expression in normal breast tissue and primary and metastatic breast cancers. We found that EpCAM is overexpressed 100- to 1000-fold in primary and metastatic breast cancer. Silencing EpCAM gene expression with EpCAM short interfering RNA (siRNA) resulted in a 35-80% decrease in the rate of cell proliferation in four different breast cancer cell lines. EpCAM siRNA treatment decreased cell migration by 91.8% and cell invasion by 96.4% in the breast cancer cell line MDA-MB-231 in vitro. EpCAM siRNA treatment was also associated with an increase in the detergent-insoluble protein fraction of E-cadherin, alpha-catenin, and beta-catenin, consistent with the known biology of EpCAM as a regulator of cell adhesion. Our hypothesis is that modulation of EpCAM expression can affect cell migration, invasion, and proliferation by enhancing E-cadherin-mediated cell-to-cell adhesion. These data provide compelling evidence that EpCAM is a potential novel target for breast cancer gene therapy and offer insights into the mechanisms associated with EpCAM gene silencing.