Tyrphostin induced growth inhibition: Correlation with effect on p210(bcr-abl) autokinase activity in K562 chronic myelogenous leukemia

We have examined a series of tyrosine kinase inhibitors structurally related to erbstatin (tyrphostins) for inhibition of p210(bcr-abl) autokinase activity in vitro and for growth inhibition of chronic myelogenous leukemia (CML) K562 cells. Of the tyrphostins with IC₅₀ for growth <50 μM, AG814, AG946, AG952, AG896, AG953, AG956 and AG957 (structurally related to lavendustin A and piceatannol) completely inhibited p210(bcr-abl) kinase activity in an immune complex kinase assay. Another group of tyrphostins (AG807, AG568, AG763, AG1076, AG490, AG1318, AG556, AG1319, AG555 and AG1111) inhibits growth of K562 cells but not p210(bcr-abl) tyrosine kinase activity. Of the compounds which inhibit growth and p210(bcr-abl) tyrosine kinase activity, AG957 inhibits DNA synthesis as early as 2 h (60% inhibition at 20 μM of AG957), a time and concentration of drug where RNA and protein synthesis were not affected. AG957 inhibits p210(bcr-abl) tyrosine phosphorylation in living cells by 1 h without an inhibition of total protein phosphorylation. Growth inhibition by AG957 was reversible after 4 h of exposure, but irreversible after 24 h. AG957 can be considered as an important lead structure for the development of anti-bcr-abl tyrosine kinase antagonists. These data also raise the possibility that bcr-abl kinase activity is directly linked to maintenance of DNA synthesis in Philadelphia chromosome positive (Ph⁺) CML cells.