bcr/abl expression in 32D cl3(G) cells inhibits apoptosis induced by protein tyrosine kinase inhibitors.

Eight protein tyrosine kinase inhibitors with in vitro epidermal growth factor receptor kinase 50% inhibitory concentration values ranging from 0.043 to 22 microM were studied for their ability to inhibit the growth of the murine interleukin-3 (IL-3) dependent myeloid 32D cl3(G) cell line and, a subclone (LG7) transformed to IL-3 independent growth by retroviral transduction and expression of the chronic myelogenous leukemia-associated protein tyrosine kinase p210bcr/abl. Cell proliferation 50% inhibitory concentration values ranged from 4 to 250 microM, and one compound was not inhibitory at 500 microM. The dose-cell proliferation curves were remarkably similar for parental 32D cl3(G) cells + IL-3 and LG7 +/- IL-3, and reversion of LG7 cells to IL-3 dependence was not observed, suggesting that none of the compounds tested could selectively inhibit p210bcr/abl. However, 6 compounds induced the appearance of a 200-base pair nucleosomal DNA ladder characteristic of apoptosis at 24 h in parental 32D cl3(G) cells + IL-3, which mimicked the effects of IL-3 withdrawal alone, but not in similarly growth arrested LG7 cells that eventually developed a necrotic pattern of DNA fragmentation. These studies suggest that the expression of p210bcr/abl can suppress apoptotic signal transduction and that this may contribute to the development of the myeloid hyperplasia that occurs in chronic phase chronic myelogenous leukemia.