Treatment of Human Pancreatic Cancer in Mice with Angiogenic Inhibitors

Abstract

Tumor growth is dependent on the balance of positive and negative regulators of angiogenesis. Antiangiogenic compounds inhibit endothelial cell biology in vitro and angiogenesis in vivo. Therefore antiangiogenic therapy presumes to be an effective treatment for pancreatic cancer. We wanted to determine the effect of antiangiogenic therapy on the growth of human pancreatic cancer in a mouse model. The angiogenesis inhibitors TNP-470 and antiangiogenic antithrombin III (aaATIII) were tested in vitro for their ability to inhibit endothelial cell proliferation. These inhibitors, along with the known antiangiogenic molecule endostatin, were then employed to treat two different primary human pancreatic cancers implanted subcutaneously into the dorsa of immunodeficient (SCID) mice. Treated tumors were examined histologically for microvessel density, apoptosis, and proliferation. All three inhibitors suppressed the growth of pancreatic tumors in vivo. Immunohistochemical analysis revealed increased degrees of apoptosis and reduced microvessel density in treated tumors compared to untreated tumors, although tumor cell proliferation was the same in both groups. None of the inhibitors tested significantly inhibited proliferation of human pancreatic cancer cells, although both TNP-470 and aaATIII were able to inhibit the proliferation of endothelial cells. The observed tumor suppression may be due to increased tumor cell apoptosis as a result of capillary dropout. These studies show that after the angiogenic switch in a human tumor, there is residual production of angiogenesis inhibitors.

Characterization of the Conformational Alterations, Reduced Anticoagulant Activity, and Enhanced Antiangiogenic Activity of Prelatent Antithrombin

“…Nevertheless, the greater antiangiogenic potency of prelatent antithrombin over latent and cleaved forms and the conditions we have established for producing this species suggest potential clinical applications for antitumor therapy. This is underscored by the fact that the antiangiogenic activity of cleaved and latent forms of antithrombin is already comparable with that of other well established angiogenesis inhibitors, such as endostatin and TNP-470 (16,20).…”

“…Such conformational alterations transform the native metastable protein to a much more stable but inactive form in which the reactive loop has inserted into the major ␤-sheet, the A-sheet, of the serpin (17,18). These conformationally altered forms of antithrombin are produced under physiologic conditions (19) and have antiangiogenic activity comparable with that of other naturally produced angiogenesis inhibitors (20). The requirement for conformational change to generate antiangiogenic activity sets antithrombin apart from other serpins, such as pigment epithelium-derived factor, maspin, and kallistatin, which have been shown to also possess antiangiogenic activity but without the need for conformational change (21)(22)(23).…”

Antiangiogenic Treatment with the Three Thrombospondin-1 Type 1 Repeats Recombinant Protein in an Orthotopic Human Pancreatic Cancer Model

“…Actually, a synergy between thrombospondin-1 and anti-VEGF small interfering RNA had been reported using a mouse fibrosarcoma model (44). Endostatin is another endogenous angiogenesis inhibitor, which showed therapeutic effects in s.c. pancreatic cancer models (45,46). Because endostatin and thrombospondin-1 exert antiangiogenic activity via different pathways (19), therapeutic contributions of these agents may be further investigated.…”

Antiangiogenic Antithrombin Blocks the Heparan Sulfate-dependent Binding of Proangiogenic Growth Factors to Their Endothelial Cell Receptors

“…FGF-2 2 and VEGF (5,9,14). Previous results including those from our group have demonstrated that cleaved and latent forms of antithrombin exert their antiangiogenic effects by inducing cell apoptosis (9,15,16), inhibiting endothelial cell cycle progression (17), and suppressing the expression of the proangiogenic heparan sulfate proteoglycan (HSPG) perlecan, as well as other proangiogenic genes in cultured HUVECs (16,17). However, the molecular mechanisms of antithrombin antiangiogenic action still remain to be defined.…”