BMC Cancer Research article Recombinant AAV-mediated HSVtk gene transfer with direct intratumoral injections and Tet-On regulation for implanted human breast cancer LI Zi-Bo†, ZENG Zhao-Jun†, CHEN Qian, LUO Sai-Qun and HU Wei-Xin* BioMed Central Open Access Address: Molecular Biology Research Center, Xiangya Medical College, Central South University, 110 Xiangya Road, Changsha, Hunan 410078, P. R. China Email: LI Zi-Bo - Lzb1022@hotmail.com; ZENG Zhao-Jun - zengzj71@hotmail.com; CHEN Qian - chenqian1977@hotmail.com; LUO Sai- Qun - luosq100@yahoo.com.cn; HU Wei-Xin* - weixinhu@xysm.net * Corresponding author †Equal contributors Published: 16 March 2006 BMC Cancer2006, 6:66 doi:10.1186/1471-2407-6-66 This article is available from: http://www.biomedcentral.com/1471-2407/6/66 Received: 01 July 2005 Accepted: 16 March 2006 © 2006Zi-Bo et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract 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 ≥104 /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 ≥104 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. Page 1 of 8 (page number not for citation purposes)