PENTOXIFYLLINE INHIBITS HYPOXIA-INDUCED UP-REGULATION OF TUMOR-CELL TISSUE FACTOR AND VASCULAR ENDOTHELIAL GROWTH-FACTOR

Tissue factor (TF), the membrane glycoprotein that initiates blood coa gulation, is constitutively expressed by many tumor cells and is impli cated in peri-tumor fibrin deposition and hypercoagulability in cancer . Upregulation of tumor TF correlates with enhanced metastatic potenti al. Furthermore, TF has been colocalized with VEGF in breast cancer, s pecially at sites of early angiogenesis. There are no data on the effe ct of hypoxia on tumor cell TF expression. Since hypoxia is known to s timulate VEGF production, we studied whether this also induces tumor c ell TF expression. Confluent monolayers of A375 melanoma, MCF-7 breast carcinoma and A549 lung carcinoma were cultured in either 95% air, 5% CO2 (normoxic) or 95% N2, 5% CO2 (hypoxic; 25-30 mmHg) for 24 h. Proc oagulant activity (PCA) was measured by amidolytic and clotting assays , surface TF antigen by flow cytometry, early apoptosis by annexin V b inding and VEGF levels in culture supernatants by ELISA. Hypoxia signi ficantly increased tumor cell PCA in all three cell lines tested and T F antigen on A375 cells was increased four-fold (P < 0.05). Pentoxifyl line (PTX), a methylxanthine derivative, significantly inhibited the h ypoxia-induced increase in PCA as well as VEGF release in all three ce ll lines tested. In A375 cells, PTX significantly inhibited TF antigen expression by both normoxic and hypoxic cells. Hypoxia induced a slig ht (5%) but not significant, increase in early apoptosis. Intravenous injection of hypoxic A375 cells into nude rats produced more pronounce d thrombocytopenia (n = 5, P < 0.01) and more lung metastases (n = 3, P < 0.05) compared to normoxic cells. We conclude that hypoxia increas es TF expression by malignant cells which enhances tumor cell-platelet binding and hematogenous metastasis. Hypoxia-induced upregulation of TF appears to parallel that of VEGF, although the mechanism remains un clear.