1. ¹Division of Experimental Therapeutics, Ontario Cancer Institute, University Health Network, Toronto, ON, Canada M5G 2M9
2. ²Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
3. ³Department of Anatomical and Cellular Pathology; Chinese University of Hong Kong, Shatin, Hong Kong
4. ⁴UMR 1698, Institut Gustave Roussy, Villejuif, France
5. ⁵Advanced Medical Discovery Institute, Princess Margaret Hospital/Ontario Cancer Institute, University Health Network, Toronto, ON, Canada M5G 2M9
6. ⁶Department of Surgical Oncology, University Health Network, Toronto, ON, Canada M5G 2M9
7. ⁷Department of Surgery, University of Toronto, Toronto, ON, Canada
8. ⁸Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada
9. ⁹Department of Radiation Oncology, University Health Network, Toronto, ON, Canada M5G 2M9

Correspondence: Fei-Fei Liu, Department of Radiation Oncology, Princess Margaret Hospital/Ontario Cancer Institute, 610 University Avenue, Toronto, Ontario, Canada M5G 2M9. Fax: +1-416-946-4586. E-mail: Fei-Fei.Liu@rmp.uhn.on.ca

Received 7 April 2004; Accepted 17 May 2004.

Abstract

We have previously demonstrated a 1000-fold induction of gene expression exclusive to Epstein–Barr virus (EBV)-positive nasopharyngeal carcinoma (NPC) cells using an adenoviral vector (ad5.oriP). This platform allows us to explore tumor-specific gene therapy with Bim_S (ad5.oriP.Bim_S), a potent proapoptotic Bcl-2 family member. Ad5.oriP.Bim_S (25 infectious units (ifu)/cell) reduced C666-1 viability in a time- and dose-dependent manner to 15% survival. The effect was enhanced with radiation (6 Gy). Three days after infection, the proportion of apoptotic cells increased from 3.5% (control) to 47.5% (25 ifu/cell). Confocal microscopy demonstrated Bim colocalization to the mitochondria within 18 h of ad5.oriP.Bim_S infection. Ad5.oriP.Bim_S induced a 2.8-, 2.1-, and 1.85-fold increase in caspase-3, -8, and -9 activities, respectively. When C666-1 cells were infected with ad5.oriP.Bim_S (20 ifu/cell), no tumors formed in 7/9 mice followed for 100 days. Six intratumoral injections of ad5.oriP.Bim_S (1.5 10⁹ ifu/dose) in combination with radiation were sufficient to cause almost complete disappearance of established C666-1 or C15 xenograft tumors. Intravenous injections of ad5.oriP.Bim_S (10⁹ ifu) induced mild perturbation in liver function tests, associated with hepatocyte apoptoses and mitoses. This vector appears to be safe and effectively cytotoxic to EBV-positive NPC cells both in vitro and in vivo, mediated primarily through the induction of apoptosis.