Tumor production of angiostatin is enhanced after exposure to TNF-alpha.

Infection of tumors with an adenoviral vector expressing a chimeric gene composed of the CArG elements of the Egr-1 promoter and a cDNA encoding TNF-alpha (Ad.Egr-TNF) has previously been shown to result in the production of high intratumoral levels of TNF-alpha and thereby tumor regression. The antitumor effects of TNF-alpha were ascribed to vascular thrombosis. We and others, have reported that inhibition of tumor vessel thrombosis using anticoagulation therapy does not abrogate the antitumor effects after TNF-alpha treatment. To investigate the potential antiangiogenic effects of TNF-alpha, we studied the generation of angiostatin after intratumoral injection of Ad.Egr-TNF. We report an increase in plasma angiostatin levels both during and after treatment with Ad.Egr-TNF that parallel tumor regression. We also report that TNF-alpha enhances angiostatin production by inducing the activity of plasminogen activator and the release of MMP-9 by tumor cells. These studies support a model in which the antiangiogenic effects of TNF-alpha on the tumor microvasculature are mediated by generation of angiostatin.

Antimetastatic effectiveness of amifostine therapy following surgical removal of Sa-NH tumors in mice.

The effects of dose per fraction on the ability of amifostine exposure to elevate angiostatin levels in the serum of mice and to inhibit spontaneous metastases formation using the well-characterized murine Sa-NH sarcoma were investigated. Amifostine was administered intraperitoneally at doses of 50, 100, or 200 mg/kg every other day for 6 days to C3Hf/Kam mice until tumors reached an average size of 8 mm in diameter. Amifostine was again administered immediately following surgical removal of the tumor-bearing limbs by amputation, and then once more 2 days later. Nontumor-bearing control animals were treated using the same dosing and surgery schedules. The average number of pulmonary metastases per animal was determined for each experimental group. A significant reduction (P <.05) in the average number of pulmonary metastases was observed only in the group of animals exposed to a dose per fraction of 50 mg/kg. A dose of 100 mg/kg was less effective while 200 mg/kg had no effect on metastases formation in this study. The effects of amifostine exposure on serum levels of the angiogenesis inhibitor angiostatin were also determined using Western analysis. Correlating with the antimetastatic effect measured, exposure of animals to 50 mg/kg of amifostine resulted in a four-fold enhanced serum level of angiostatin above control levels. This phenomenon occurred in both tumor-bearing as well as nontumor-bearing animals. In contrast, a dose of 200-mg/kg amifostine administered intraperitoneally under these conditions had no measurable effect on angiostatin serum levels in this animal system. The enhanced ability of relatively low doses of amifostine to inhibit spontaneous metastases formation suggests that effective antimetastatic therapies with amifostine can be designed with minimal toxic side effects. While the dose responses for angiostatin production and metastases inhibition by amifostine are well correlated, the precise mechanism of action underlying these phenomena is unclear but is suggestive of a redox driven process(es).