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Angiogenic Factor Thymidine Phosphorylase Increases Cancer Cell Invasion Activity in Patients with Gastric Adenocarcinoma

We investigated the biological role of thymidine phosphorylase (TP), an angiogenic factor, in gastric cancer cell migration and invasion and explored a therapeutic approach for high TP-expressing tumors using TP enzymatic inhibitor (TPI) and rapamycin. We established TP cDNA overexpressing gastric cancer cell lines (MKN-45/TP and YCC-3/TP) and did invasion and adhesion assays with Matrigel-coated transwell membranes. The related signal pathway using recombinant human TP (rhTP), deoxy-d-ribose (D-dRib), and signal pathway inhibitors (wortmannin, LY294002, and rapamycin) was investigated. First, AGS and MKN-1 gastric cancer cell lines showed dose-dependent up-regulation of invasiveness through Matrigel following treatment with rhTP or D-dRib. TP-overexpressing cancer cell lines displayed increased migration and invasion activity, which doubled with rhTP and D-dRib treatment. This activity depended on the enzymatic activity of TP, and TP stimulated the adhesion of cancer cells onto Matrigel and induced actin filament remodeling. Finally, we showed that this activity is related to increased phosphatidylinositol 3-kinase activity in TP-overexpressing cells and that combination treatment with rapamycin and TP enzymatic inhibitor produces an additive effect to abrogate TP-induced invasion. Taken together, TP increases the migration and invasion of gastric cancer cells, especially in TP-expressing cells. Therapies targeting TP might diminish the propensity for invasion and metastasis in gastric cancer. (Mol Cancer Res 2008;6(10):1554–66)