Contortrostatin, a dimeric disintegrin from Agkistrodon contortrix contortrix, inhibits breast cancer progression

We report the results of a multidisciplinary study on the inhibitory effect of a snake venom disintegrin, contortrostatin, a 13.5 kDa homodimeric prot ein isolated from Agkistrodon contortrix contortrix (southern copperhead) v enom, on breast cancer progression. We demonstrate that contortrostatin bin ds to integrins and blocks the adhesion of human breast cancer cells (MDA-M B-435) to extracellular matrix (ECM) proteins including fibronectin and vit ronectin, but it has no effect on adhesion of the cells to laminin and Matr igel. Contortrostatin also prevents invasion of MDA-MB-435 cells through an artificial Matrigel basement membrane. Daily local injection of contortros tatin (5 mu g per mouse per day) into MDA-MB-435 tumor masses in an orthoto pic xenograft nude mouse model inhibits growth of the tumor by 74% (p = 0.0 164). More importantly, it reduces the number of pulmonary macro-metastasis of the breast cancer by 68% (p < 0.001), and micro-metastasis by 62.4% (p < 0.001). Contortrostatin is not cytotoxic to cancer cells, and does not in hibit proliferation of the breast cancer cells in vitro. However, contortro statin inhibits angiogenesis induced by the breast cancer, as shown by immu nohistochemical quantitation of the vascular endothelial cells in tumor tis sue removed from the nude mice. We have identified alpha v beta 3, an impor tant integrin mediating cell motility and tumor invasion, as one of the bin ding sites of contortrostatin on MDA-MB-435 cells. We conclude that contort rostatin blocks alpha v beta 3, and perhaps other integrins, and thus inhib its in vivo progression.