STRUCTURE-ACTIVITY-RELATIONSHIPS IN A SERIES OF 5-[(2,5-DIHYDROXYBENZYL)AMINO]SALICYLATE INHIBITORS OF EGF-RECEPTOR-ASSOCIATED TYROSINE KINASE - IMPORTANCE OF ADDITIONAL HYDROPHOBIC AROMATIC INTERACTIONS

Potent inhibitors of EGF-dependent protein tyrosine kinase (PTK) activ ity were synthesized in a series of 5-[(2,5-dihydroxybenzyl)amino]sali cylates. Several of these compounds inhibited EGF-dependent DNA synthe sis in ER 22 cells with IC50 < 1 muM. In this series of PTK inhibitors , the role of the salicylate moiety as a potential divalent ion chelat or was tested and found to be nonessential in all cases. The length an d ramification of the substituting carboxyl group were investigated to improve cellular bioavailability, and this analysis provided compound s with increased inhibitory effect on EGF-induced DNA synthesis. Salic ylates esterified with long hydrophobic chains were shown to be noncom petitive inhibitors of ATP, in contrast to the free acid and methyl sa licylate. Moreover, all the tested inhibitors were shown to be noncomp etitive inhibitors of the peptide substrate. Structure-activity relati onships allowed us to suspect a hydrophobic pocket in the tyrosine kin ase domain, preferentially interacting with aromatic rings. Finally, t he selectivity of the best inhibitors was tested against other kinases , and they were found to be selective for tyrosine kinase. They were a lso shown to be good inhibitors of EGF-receptor autophosphorylation.