<P>We identified a specific interaction between TSP1 and versican, that is induced during a toll-like receptor-3-dependent inflammatory response in vascular smooth muscle cells. TSP1 binding to versican is modulated by divalent cations. This interaction is mediated by interaction of the G1 domain of versican with the N-module of TSP1 but only weakly with the corresponding N-terminal region of TSP2. The G1 domain of versican contains two Link modules, which are known to mediate TNF &alpha;-stimulated gene-6 protein binding to TSP1, and the related G1 domain of aggrecan is also recognized by TSP1. Therefore, TSP1 interacts with three members of the Link-containing hyaladherin family. On the surface of poly-I:C-stimulated vascular smooth muscle cells, versican organizes into fibrillar structures that contain elastin but are largely distinct from those formed by hyaluronan. Endogenous and exogenously added TSP1 incorporates into these structures. Binding of exogenous TSP1 to these structures, to purified versican, and to its G1 domain is potently inhibited by heparin. At higher concentrations, exogenous TSP1 delays the poly-I:C induced formation of structures containing versican and elastin, suggesting that TSP1 negatively modulates this component of a vascular smooth muscle inflammatory response.</p> <P> Angiogenesis involves multiple signaling pathways that must be considered for developing agents to modulate pathological angiogenesis. Because both cyclooxygenase inhibitors and dithioles have demonstrated anti-angiogenic properties, we investigated the activities of a new class of antiinflammatory drugs containing dithiolethione moieties (S-NSAIDs) and S-valproate. Dithiolethione derivatives of diclofenac, valproate, and sulindac inhibited endothelial cell proliferation and induced Ser78 phosphorylation of hsp27, a known molecular target of anti-angiogenic signaling. The parent drugs lacked this activity, but dithiolethiones were active at comparable concentrations. Although dithiolethiones can potentially release hydrogen sulfide, NaSH did not replicate some activities of the S-NSAIDs, indicating that the dithioles regulate angiogenesis through other mechanisms. In contrast to the parent drugs, S-NSAIDs, S-valproate, NaSH, and dithiolethiones were potent inhibitors of angiogenic responses in muscle and HT29 tumor explants assessed by 3-dimensional collagen matrix assays. Dithiolethiones and valproic acid were also potent inhibitors of developmental angiogenesis in zebrafish embryos, but the S-NSAIDs, remarkably, lacked this activity. S-NSAIDs and S-valproate have potent anti-angiogenic activities mediated by their dithiole moieties. The novel properties of S-NSAIDs and S-valproate to inhibit pathological versus developmental angiogenesis suggest that these agents may have a role in cancer treatment.</p>