The antithrombotic compound
nafazatrom was evaluated in several in vivo and in vitro assays to elucidate the mechanism of its antimetastatic activity. C57BL/6 mice bearing B16 amelanotic subcutaneous
tumors treated with 100 mg
nafazatrom/kg/day exhibited a sixfold reduction in metastatic pulmonary lesions compared to lesion numbers in controls. The reduction in metastatic lesions was not accompanied by changes in primary
tumor growth, and up to 1 microgram
nafazatrom/ml did not inhibit
tumor cell proliferation in vitro. Treatment of C57BL/6 mice with
nafazatrom prior to iv inoculation of
tumor cells failed to inhibit lung colony formation. In vitro exposure of exponentially growing B16 amelanotic cells to
nafazatrom (1 microgram/ml for 72 hr) in culture did not change their ability to adhere to endothelial cell monolayers. B16 amelanotic cells degraded the matrix material of bovine endothelial cell monolayers; a
heparin sulfate proteoglycan appeared to be the predominant matrix component released by these
tumor cells, as judged by resistance to
chondroitin ABC lyase and sensitivity to
heparitinase and
pronase degradation.
Nafazatrom (1 microgram/ml for 72 hr) inhibited the solubilization of matrix components by approximately 60%.
Tumor cell degradation of matrix components is an important event in the pathogenesis of
metastasis. Thus the interference with this process appears to provide an explanation for the inhibition of malignant cell dissemination in vivo by
nafazatrom.