Tissue factor pathway inhibitor (TFPI) is the major physiologic inhibitor of the extrinsic coagulation pathway. We have previously shown that TFPI is also a potent inhibitor of endothelial proliferation in vitro and of primary and metastatic tumor growth in vivo. Surprisingly, the antitumor activity of TFPI was demonstrated to be independent of its anticoagulant activity, suggesting a possible nonhemostatic mechanism of action for TFPI in these models. This antitumor mechanism may involve the very low density lipoprotein (VLDL) receptor because the in vitro antiproliferative activity of TFPI is mediated through interaction with the VLDL receptor. In the current study, we identify a 23-amino acid fragment of TFPI (TFPIc23) localized to the C-terminus, which mediates binding to the VLDL receptor. The TFPIc23 peptide inhibits endothelial cell proliferation through an apoptotic mechanism and blocks vessel outgrowth in the in vitro assays, and this activity is mediated through interaction with the VLDL receptor. In vivo, this peptide potently inhibits angiogenesis in Matrigel and chick chorioallantoic membrane models and also inhibits metastatic tumor growth. Our data demonstrate that this VLDL receptor-binding fragment of the TFPI molecule has apoptotic, antiangiogenic, and antitumor activity and suggests a possible mechanism whereby TFPI can regulate angiogenesis and tumor growth independently of its anticoagulant activity.
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