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The extracellular matrix glycoprotein thrombospondin-1 (TSP1) inhibits angiogenesis, endothelial cell growth, motility and adhesion. Peptides from the type I repeats of TSP1 mimic the adhesive and growth inhibitory activities of the intact protein and specifically interact with heparin and transforming growth factor-beta (TGF beta). To define the structural basis for the antiangiogenic activities of these peptides, we prepared analogs of the TSP1 peptide KRFKQDGGWSHWSPWSSC. L-forward, L-reverse, and D-reverse (retro-inverso) analogs displayed identical activities for binding to heparin, demonstrating a lack of stereospecificity for heparin binding. The L-reverse and D-reverse peptides, however, had somewhat decreased abilities to activate latent TGF beta. Conjugation of the forward peptides through a C-terminal thioether and the reverse peptides through an N-terminal thioether to polysucrose abolished the adhesive activity of the peptides and enhanced their antiproliferative activities for endothelial and breast carcinoma cells stimulated by fibroblast growth factor-2. Their antiproliferative activities were independent of latent TGF beta activation, because substitution of an Ala residue for the essential Phe residue in the TSP1 type-1 repeat peptide increased their potency for inhibiting TSP1 binding to heparin and for inhibiting endothelial cell proliferation. Although the conjugated peptides were inactive in vivo, an unconjugated retro-inverso analog of the native TSP peptide inhibited breast tumor growth in a mouse xenograft model. Thus, these TSP-derived peptide analogs antagonize endothelial growth through their heparin-binding activity rather than through activation of latent TGF beta or increasing cell adhesion. These stable analogs may therefore be useful as therapeutic inhibitors of angiogenesis stimulated by fibroblast growth factor-2.

Two new sesquiterpenoids, strophanthoids A and B (1 and 2), along with seven known cardiac glycosides were isolated from the roots of Strophanthus divaricatus. Their structures were elucidated on t...

Bovine corneal endothelial cells showed a strong migratory response to specific simple sugars (D-glucose and sucrose, but not L-glucose, sorbitol, lactose, or D-galactose) at concentrations above 10 mM. Checkerboard analysis of the migratory responses in modified Boyden chambers indicated both chemotactic and chemokinetic effects. Serum starvation of the cultures increased the chemotaxis towards D-glucose and 2-deoxy-D-glucose, but not towards sucrose. Migration to sucrose and glucose was inhibited by chelation of extracellular calcium or by inhibition of Na+,K+ ATPase with ouabain. To date, this migratory response has been found only in corneal endothelial cells. Neither human melanoma cells, human breast carcinoma cells, bovine aortic endothelial cells, nor bovine microvascular endothelial cells migrated towards simple sugars, although all cell types migrated toward fibronectin in chemotaxis assays. After 16–19 passages in culture, bovine corneal endothelial cells retained their ability to migrate towards fibronectin, but lost their ability to migrate towards sugars. This loss of migratory response was accompanied by a sevenfold decrease in Na+,K+ ATPase activity. Although loss of Na+,K+ ATPase activity accompanied the loss of migratory response, pretreatment of cell cultures with 25 mM glucose did not stimulate, but rather lowered Na+,K+ ATPase activity in low or high passage cultures. © 1993 Wiley-Liss, Inc.

Thrombospondin is an inhibitor of angiogenesis that modulates endothelial cell adhesion, proliferation, and motility. Synthetic peptides from the second type I repeat of human thrombospondin containing the consensus sequence -Trp-Ser-Pro-Trp- and a recombinant heparin binding fragment from the amino-terminus of thrombospondin mimic several of the activities of the intact protein. The peptides and heparin-binding domain promote endothelial cell adhesion, inhibit endothelial cell chemotaxis to basic fibroblast growth factor (bFGF), and inhibit mitogenesis and proliferation of aortic and corneal endothelial cells. The peptides also inhibit heparin-dependent binding of bFGF to corneal endothelial cells. The antiproliferative activities of the peptides correlate with their ability to bind to heparin and to inhibit bFGF binding to heparin. Peptides containing amino acid substitutions that eliminate heparin-binding do not alter chemotaxis or proliferation of endothelial cells. Inhibition of proliferation by the peptide is time-dependet and reversible. Thus, the antiproliferative activities of the thrombospondin peptides and recombinant heparin-binding domain result at least in part from competition with heparin-dependent growth factors for binding to endothelial cell proteoglycans. These results suggest that both the Trp-Ser-Xaa-Trp sequences in the type I repeats and the amino-terminal domain play roles in the antiproliferative activity of thrombospondin.

The exocyclic substituent control of stereoselectivity, periselectivity, and regioselectivity in the unsymmetrical cycloaddition reactions of electron-deficient heptafulvenes with electron-rich fulvenes are discussed.