Transforming growth factor beta peptide antagonists and their conversion to partial agonists.

Transforming growth factor beta (TGF-beta) has been implicated in the pathogenesis of various human diseases. Synthetic TGF-beta antagonists therefore could have therapeutic utility. Here we show the development of such compounds. Three synthetic pentacosapeptides designated beta125-(41-65), beta225-(41-65), and beta325-(41-65), whose amino acid sequences correspond to the 41st to 65th amino acid residues of TGF-beta1, TGF-beta2, and TGF-beta3, respectively, inhibit the binding of 125I-labeled TGF-beta isoforms to TGF-beta receptors in mink lung epithelial cells with IC50 of approximately 0.06-2 microM. beta125-(41-65) blocks TGF-beta1-induced growth inhibition and TGF-beta1-induced plasminogen activator inhibitor-1 expression in these cells. The variants designated beta125-(41-65)W52A/D55A and beta325-(41-65)R52A/D55A, in which both Trp52/Arg52 and Asp55 are replaced by alanine residues, do not have TGF-beta antagonist activity. Multiple conjugation of beta125-(41-65) to carrier proteins enhances its antagonist activity but also confers partial agonist activity as measured by DNA synthesis inhibition. These results suggest that the (W/R)XXD motif is important for the activities of these TGF-beta peptide antagonists and that this motif may be the active site sequence of TGF-beta.