TYROSINE KINASE INHIBITORS .4. STRUCTURE-ACTIVITY-RELATIONSHIPS AMONGN-SUBSTITUTED AND 3-SUBSTITUTED 2,2'-DITHIOBIS(1H-INDOLES) FOR IN-VITRO INHIBITION OF RECEPTOR AND NONRECEPTOR PROTEIN-TYROSINE KINASES

A series of S-substituted 2,2'-dithiobis(1H-indoles) were synthesized and evaluated for their ability to inhibit the tyrosine kinase activit y of both the epidermal growth factor receptor (EGFR) and the nonrecep tor pp60(v-src) tyrosine kinase, to extend the available structure-act ivity relationships for this series. The majority of the compounds wer e prepared either by reaction of 2-chloro-1-methylindole-3-carbonyl ch loride with amines, followed by thiomethylation, demethylation, and ox idative dimerization, or by reaction of isocyanates with the anion of 1-methyl-2-indolinethione followed by dimerization. Overall, inhibitor y activity is retained by analogues having a wide variety of side chai ns. A series of 3-carboxamide analogues had moderate to good activity against isolated EGFR (IC(50)s 1-20 mu M), with monoalkyl substitution of the carboxamide being optimal. Polar side chains were generally le ss effective than lipophilic ones, with benzyl being particularly effe ctive. However, N,N-disubstitution was the most effective pattern for inhibition of pp60(v-src). A variety of substituted N-phenylcarboxamid es had lower activity against EGFR than the parent derivative, and a N -thienylcarboxamide also had low activity. A series of 3-ketones, incl uding methyl, phenyl, and furyl derivatives, showed moderate activity against the pp60(v-src) kinase, but were less effective against EGFR. The mechanism of inhibition of both kinases by these drugs was shown t o be noncompetitive with respect to both ATP and peptide substrate. Se lected compounds inhibited the growth of Swiss 3T3 cells with IC(50)s in the low micromolar range and inhibited bFGF-mediated intracellular tyrosine phosphorylation in the same cell line. Thiol inhibits the eff ects of the compounds, suggesting that one possible mechanism of inhib ition is thiol-disulfide exchange with thiol-containing residues in th e catalytic sites. Crystal structures of two representative compounds show a folded, V-shaped structure, with the disulfide bridge exposed, consistent with this hypothesis.