Matrix metalloproteinase 2 in tumor cell-induced platelet aggregation: Regulation by nitric oxide

A correlation exists between the ability of tumor cells to aggregate platel ets and their tendency to metastasize. Tumor cell-induced platelet aggregat ion (TCIPA) facilitates the embolization of the vasculature with tumor cell s and the formation of metastatic foci. It is web documented that matrix me talloproteinases (MMPs) play an integral part in tumor spread and the metas tatic cascade. Therefore, we have examined the role of MMPs during TCIPA an d its regulation by nitric oxide (NO) in vitro. Human HT-1080 fibrosarcoma and A549 lung epithelial cancer cells induced TCIPA in a concentration-depe ndent manner that was monitored by aggregometry. This aggregation resulted in the release of MMP-2 from platelets and cancer cells, as measured by zym ography. HT-1080 cells released significantly more MMP-2 than A549 cells an d were more efficacious in inducing TCIPA. Inhibition of MMP-2 with phenant hroline (1-1000 muM), a synthetic inhibitor of MMPs, and by neutralizing an ti-MMP-2 antibody (10 mug/ml) reduced TCIPA induced by HT-1080 cells. TCIPA was abolished by simultaneous inhibition of platelet function with acetyls alicylic acid (100 muM; thromboxane pathway inhibitor), apyrase (250 mug/ml ; ADP pathway inhibitor), and phenanthroline. NO donors such as S-nitroso-n -acetylpenicillamine and S-nitrosoglutathione (both at 0.01-100 muM) inhibi ted TCIPA and MMP-2 release from platelets and tumor cells. The inhibitory actions of S-nitroso-n-acetylpenicillamine and S-nitrosoglutathione were re versed by 1H-[1,2,4]oxadiazole[4,3]quinoxalin-1-one (0.01-30 muM), a select ive inhibitor of the soluble guanylyl cyclase. We conclude that (a) human f ibrosarcoma cells aggregate platelets via mechanism(s) that are mediated, i n part, by MMP-2; (b) NO inhibits TCIPA, in part, by attenuating the releas e of MMP-2; and (c) these effects of NO are cGMP-dependent.