Synergistic antitumor activity of ZD6474, an inhibitor of vascular endothelial growth factor receptor and epidermal growth factor receptor signaling, with gemcitabine and ionizing radiation against pancreatic cancer.

PURPOSE: Standard treatments have modest effect against pancreatic cancer, and current research focuses on agents targeting molecular pathways involved in tumor growth and angiogenesis. This study investigated the interactions between ZD6474, an inhibitor of tyrosine kinase activities of vascular endothelial growth factor receptor-2 and epidermal growth factor receptor (EGFR), gemcitabine, and ionizing radiation in human pancreatic cancer cells and analyzed the molecular mechanisms underlying this combination. EXPERIMENTAL DESIGN: ZD6474, ionizing radiation, and gemcitabine, alone or in combination, were given in vitro to MIA PaCa-2, PANC-1, and Capan-1 cells and in vivo to MIA PaCa-2 tumor xenografts. The effects of treatments were studied by the evaluation of cytotoxicity, apoptosis, cell cycle, EGFR and Akt phosphorylation, modulation of gene expression of enzymes related to gemcitabine activity (deoxycytidine kinase and ribonucleotide reductase), as well as vascular endothelial growth factor immunohistochemistry and microvessel count. RESULTS: In vitro, ZD6474 dose dependently inhibited cell growth, induced apoptosis, and synergistically enhanced the cytotoxic activity of gemcitabine and ionizing radiation. Moreover, ZD6474 inhibited phosphorylation of EGFR and Akt and triggered cell apoptosis. PCR analysis showed that ZD6474 increased the ratio between gene expression of deoxycytidine kinase and ribonucleotide reductase. In vivo, ZD6474 showed significant antitumor activity alone and in combination with radiotherapy and gemcitabine, and the combination of all three modalities enhanced MIA PaCA-2 tumor growth inhibition compared with gemcitabine alone. CONCLUSIONS: ZD6474 decreases EGFR and Akt phosphorylation, enhances apoptosis, favorably modulates gene expression in cancer cells, and acts synergistically with gemcitabine and radiotherapy to inhibit tumor growth. These findings support the investigation of this combination in the clinical setting.

Radiation-induced changes in nucleotide metabolism of two colon cancer cell lines with different radiosensitivities.

PURPOSE: To investigate changes in nucleotide metabolism after irradiation. MATERIALS AND METHODS: HT29 and SW48 human colon carcinoma cells were exposed to 60Co gamma-rays at doses ranging from 0 to 7.5 Gy. At different times after irradiation, the activities of nine enzymes involved in nucleotide metabolism were measured, the levels of thymidine kinase and deoxycytidine kinase proteins were evaluated by Western blot, and cell-cycle kinetics were analysed by flow cytometry. RESULTS: Changes in enzyme activities concerned not purine but pyrimidine metabolism and essentially the salvage pathway for deoxyribonucleotide synthesis. They were greater in the less radiosensitive HT29 cells. The levels of thymidine kinase and deoxycytidine kinase proteins changed in parallel with their activities. The metabolic changes in irradiated cells did not seem to be due to S-phase transition and the pattern of enzyme activity changes was different from that observed in proliferative cells. CONCLUSIONS: Radiation-induced changes in the salvage pathway for pyrimidine deoxyribonucleotide synthesis were observed. These findings could be exploited in cancer therapy because higher enzyme activities after irradiation suggest that radiation exposure may render cells more sensitive to the drugs activated by these enzymes.