The predictive and therapeutic value of thymidine phosphorylase and dihydropyrimidine dehydrogenase in capecitabine (Xeloda)-based chemotherapy for head and neck cancer.

OBJECTIVES: To evaluate whether two molecular biomarkers, thymidine phosphorylase (TP) and dihydropyrimidine dehydrogenase (DPD), could be clinically useful in predicting and improving the chemotherapeutic outcome of the oral fluoropyrimidine capecitabine (5'-DFUR or Xeloda), in the treatment of human head and neck squamous cell carcinoma (HNSCC). EXPERIMENTAL DESIGN: Quantitative reverse-transcriptase polymerase chain reaction was used to determine the TP and DPD expression levels in different HNSCC cell lines. The TP to DPD ratio was calculated and compared to the relative chemosensitivity between cell lines after treatment with 5'-DFUR. The effect of TP transgene expression to alter the TP to DPD ratio and hence optimize the therapeutic outcome of capecitabine treatment was further evaluated in a murine model of human HNSCC using immunohistochemistry to detect TP and DPD expression in vivo. RESULTS: No correlation was detected between sensitivity to 5'-DFUR and the relative expression levels of TP or DPD in the multiple HNSCC cell lines tested. However, significant correlation was observed between the TP to DPD ratio versus drug resistance of the HNSCC cells (r = -0.914, p = 0.0281). In addition, we demonstrate that transgene expression of TP significantly enhanced the tumoricidal effect of capecitabine in HNSCC tumors with otherwise low endogenous TP to DPD ratios. This antitumor effect was observed up to 30 days after treatment. CONCLUSIONS: The results of this study suggest that HNSCC patients who would most benefit from capecitabine-based chemotherapy could be identified by examining the TP to DPD ratio of their tumors. Furthermore, we demonstrate the potential role of TP gene therapy in TP to DPD ratio manipulation to optimize the tumoricidal effect of capecitabine.

Molecular disruption of the MRN(95) complex induces radiation sensitivity in head and neck cancer.

OBJECTIVES/HYPOTHESIS: The goal of the project was to develop a novel treatment strategy for head and neck cancer that induces radiation sensitivity. We hypothesized that the normal cellular DNA repair response in head and neck squamous cell carcinoma after radiation therapy can be blocked by a dominant negative disruption of the functioning MRN(95) protein complex. To test this hypothesis, we have developed a novel molecular therapy that inhibits the MRN(95) complex in tumor cells. Disruption the MRN(95) complex and thus DNA repair should result in enhanced tumor killing after classic external-beam radiation therapy. STUDY DESIGN: Experiments with human head and neck squamous cell carcinoma cell lines in vitro were performed. METHODS: Recombinant adenovirus vectors carrying the genes for enhancing radiation were generated. Human head and neck squamous cell carcinoma cells were treated with recombinant adenovirus vectors carrying the mutated p95 gene (p95-300), which contains the C-terminus 300 amino acids of the Nbs1(p95) protein. Tumor cells were also treated with adenovirus vector carrying full-length p95 protein or DL312 control virus; then all cell lines were subjected to 2 Gy irradiation. Cell growth curves were determined through colorimetric tetrazolium salt assay. RESULTS: Both the Ad-p95-300 and Ad-p94-his (full-length wild-type gene) demonstrated significant antitumor effect alone and in combination with radiation therapy compared with control samples. Cell cycle analysis demonstrated a shift toward the G2/M phase of the cell cycle. Analysis of telomerase activity demonstrated a significant decrease in telomerase activity after molecular therapy alone, and a greater decrease when combined with radiation therapy. CONCLUSION: Adenovirus-mediated mutant or full-length p95 molecular therapy demonstrated efficacy for the treatment of head and neck squamous cell carcinoma in vitro. This novel molecular therapy strategy induced significant radiation sensitization, induced a relative G2/M arrest, and decreased telomerase activity, all of which enhance the benefit of radiation therapy.