Targeted Chemotherapy for Head and Neck Cancer with a Chimeric Oncolytic Adenovirus Coding for Bifunctional Suicide Protein FCU1

Abstract

Purpose: Transfer of prodrug activation systems into tumors by using replication-deficient viruses has been suggested to be an effective method for achieving high local and low systemic anticancer drug concentrations. However, most current suicide gene therapy strategies are still hindered by poor efficiency of in vivo gene transfer, inefficient tumor penetration, limited bystander cell killing effect, and need of large prodrug doses. We hypothesized that local amplification provided by a replication competent platform would help overcome these limitations.Experimental Design: We generated a transductionally and transcriptionally targeted oncolytic adenovirus Ad5/3-Δ24FCU1 expressing the fusion suicide gene FCU1. FCU1 encodes a bifunctional fusion protein that efficiently catalyzes the direct conversion of 5-FC, a relatively nontoxic antifungal agent, into the toxic metabolites 5-fluorouracil and 5-fluorouridine monophosphate, bypassing the natural resistance of certain human tumor cells to 5-fluorouracil.Results: We examined the efficacy of Ad5/3-Δ24FCU1 and the replication-defective control Ad5/ 3-FCU1 with and without 5-FC. FCU1 expression was confirmed by Western blot, whereas enzymatic conversion levels in vitro and in vivo were determined by high-performance liquid chromatography separation. Significant antitumor effect was observed in vitro and in vivo in a murine model of head and neck squamous cell carcinoma. Although we observed a decrease in viral DNA copy number in vitro and in tumors treated with Ad5/3-Δ24FCU1 and 5-FC, suggesting an effect on virus replication, the highest antitumor effect was observed for this combination.Conclusions: It seems feasible and efficacious to combine adenovirus replication to the FCU1 prodrug activation system. Clin Cancer Res; 16(9); 2540-9. ©2010 AACR.Each year, >615,000 new head and neck cancer cases are diagnosed worldwide (1). Approximately 90% of them are squamous-cell carcinomas (HNSCC). HNSCC is an umbrella term that includes cancers at several sites (e.g., oral cavity, pharynx, and larynx) having different etiologies and prognoses while sharing common risk factors and treatment options (2). Currently, the standard of care for HNSCC includes surgery, radiotherapy, chemotherapy, monoclonal antibodies, and combinations of these. Despite steady progress in treatment outcomes, the overall 5-year survival rate is below 50%, unchanged for nearly three decades. Surgery can be mutilating and often has significant effects on swallowing and speech. The addition of chemotherapy to radiotherapy has been useful in the context of organ preservation, but has resulted in limited improvement in survival rates (3). Cisplatin and 5-fluorouracil (5-FU) remain the standard chemotherapy agents for HNSCC. Mortality associated with disease and morbidity associated with its treatments have encouraged the pursuit of alternative therapeutic strategies.5-FU is a pyrimidine analogue that requires cellular uptake and metabolic activation to exert cytotoxicity. As a uracil analogue, ...

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