Protein-tyrosine kinases (PTK's) offer unique targets for anticancer drug design. The association of increased tyrosine phosphorylation with increased cell proliferation resulting from both retroviral transformation and the action of polypeptide growth factors presents a compelling case for a critical role for PTK's in the control of cell growth. Specific inhibitors of the PTK's might therefore be useful in controlling cancer cell growth and expression of the transformed phenotype. They may also have value in elucidating the biochemical mechanisms by which the PTK's act. In order to prepare PTK inhibitors having maximum potency and specificity, analogs of known peptide substrates of the PTK's will be synthesized in which the normally phosphorylated tyrosine residues are replaced by residues that will, after they are activated by phophorylation, bind covalently to the active sites of the enzymes. This will result in a series of potential suicide substrates that will be studied in order to determine the structural features associated with maximum inhibitory activity. In addition, it is known that phosphorylation of a tyrosine residue located near the C-terminus of the PTK's inhibits their kinase activity. Phosphotyrosine-containing peptide fragments of this region will therefore also be synthesized and tested for inhibitory activity. The effect that the proposed inhibitors have on in vitro protein kinase assays will be determined. Analogs that appear to be effective inhibitors will be further examined to determine 1) their apparent Ki values, 2) their kinetic mechanisms of action, 3) the substrate sites for which they compete, 4) the time course and ATP-dependence of enzyme inactivation, 5) the ability of the proposed inhibitors to act as alternate substrates, and 6) their specificity. A study will also be conducted of how they alter the growth properties and morphology of cells that are transformed due to the overexpression of PTK activity.
