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.

Mutant Nbs1 enhances cisplatin-induced DNA damage and cytotoxicity in head and neck cancer.

OBJECTIVE: Enhanced DNA double-strand break (DSB) repair could be a primary cause for development of resistance in tumor cells to cisplatin, which induces crosslinks and DNA DSBs. A protein complex consisting of hMre11, hRad50, and Nbs1 (MRN) has been identified as a critical component in repair of DNA DSBs. The present study investigates whether the expression of a truncated form of Nbs1 interrupts the function of the MRN complex and therefore enhances cisplatin-induced DNA damage and cytotoxicity in human head and neck squamous cell carcinoma (HNSCC). METHODS AND MEASURES: Two human HNSCC cell lines, JHU006 and JHU029, were used. A dominant negative recombinant adenovirus expressing domains of Nbs1 was constructed. Adenovirus-mediated mutant Nbs1 (Ad-Nbs1) gene transfer was performed with replication-defective virus (DL312) and no treatment as controls. Transgene expression and cell viability were evaluated in transfected cells. Neutral comet assay was performed and the "tail moment," the product of the amount of DNA in the tail and the distance of tail migration, was analyzed for evaluating DNA DSB damage at 24, 48, and 72 hours. RESULTS: Transgene expression of mutant Nbs1 was confirmed by Western blotting. Ad-Nbs1 gene transfer significantly increased cisplatin-induced cytotoxicity as shown by stunting of 6-day growth curves. Neutral comet analysis revealed that the mean tail moment, indicative of DNA damage, was significantly elevated in cells treated with combined cisplatin and Ad-Nbs1 compared to cisplatin alone in both cell lines. CONCLUSIONS: Expression of mutant Nbs1 significantly increases cisplatin-induced DNA DSBs and cytotoxicity. The increase in double-strand DNA damage corresponds to the level of cytotoxicity in the different treatment groups and suggests that tumor chemosensitization occurs through augmentation of DNA DSBs. CLINICAL SIGNIFICANCE: Alteration of DNA repair may provide a novel approach to enhancing sensitivity of HNSCC to chemotherapy. Our study supports the potential application of Ad-Nbs1 in combination with cisplatin for treatment of advanced and metastatic HNSCC.