EFFECT OF THE PROTEIN-TYROSINE KINASE INHIBITOR GENISTEIN ON NORMAL AND LEUKEMIC HEMATOPOIETIC PROGENITOR CELLS

Receptor and nonreceptor protein tyrosine kinases (PTKs) play a key ro le in the control of normal and neoplastic cell growth. The availabili ty of PTK inhibitors prompted us to evaluate the effects of genistein, a natural inhibitor of PTKs, on in vitro colony formation by normal m ultilineage colony-forming units (CFU-Mix), erythroid bursts (BFU-E), granulocyte-macrophage colony-forming units (CFU-GM), long-term cultur e-initiating cells (LTC-IC) and acute myelogenous leukaemia colony-for ming units (CFU-AML). Continuous exposure of normal marrow and blood m ononuclear non-adherent cells, blood CD34(+)CD45RA(-) cells, and leuka emic blasts to increasing doses of genistein (1-100 mu M) resulted in a statistically significant (P less than or equal to 0.05) dose-depend ent suppression of CFU-Mix, BFU-E, CFU-GM and CFU-AML growth, Regressi on analysis showed that growth inhibition was linearly related to geni stein concentration. Genistein dose causing 50% inhibition (ID50) of C FU-AML was significantly lower compared to CFU-GM ID50 for marrow (19 v 32 mu M, P less than or equal to 0.017), unseparated blood (19 v 44 mu M, P less than or equal to 0.028) or CD34(+)CD45RA(-) blood (19 v 3 6, P less than or equal to 0.04). Preincubation of leukaemic blasts wi th genistein (200 mu M) for 1-2 h confirmed that CFU-AML were signific antly more sensitive than normal marrow and blood CFU-GM to genistein, Preincubation conditions which maximally suppressed leukaemic and nor mal colony growth spared a substantial percentage of marrow (29 +/- 4% ) and blood (40 +/- 3%) LTC-IC. In conclusion, our data demonstrate th at: (a) genistein strongly inhibits the growth of normal and leukaemic haemopoietic progenitors; (b) growth inhibition is dose- and time-dep endent; (c) leukaemic progenitors are more sensitive than normal proge nitors to genistein-induced growth inhibition: (d) genistein exerts a direct toxic effect on haemopoietic cells while sparing a substantial proportion of LTC-IC, The potent CFU-AML growth inhibition associated with the relative resistance of normal LTC-IC strongly supports the us e of genistein for marrow purging.