Molecular mechanisms of ZD1839 (Iressa)-induced apoptosis in human leukemic U937 cells.

Aim: To investigate the molecular mechanisms of ZD1839-induced apoptosis in human leukemic U937 cells. Methods: The inhibition of human leukemic U937 cell growth was assessed by 3- (4, 5-dimethyl-2-thiazolyl)-2, 5-diphnyl-2 H-tetrazolim bromide (MTT) assays, lactate dehydrogenase (LDH) release, and cell cycle distribution. The expression of anti- and pro-apoptotic proteins was detected by Western blot analysis. Results: This study demonstrated that ZD1839 induced apoptosis in leukemic U937 cells by the downregulation of Bcl-2, caspase activation and subsequent apoptotic features. Cotreatment with ZD1839 and the caspase-3 inhibitor z-DEVD-fmk blocked apoptosis, indicating that caspase-3 activation is at least partially responsible for ZD1839-induced apoptosis. The ectopic expression of Bcl-2 attenuated caspase-3 activation, PARP cleavage, and subsequent indicators of apoptosis, including sub-G₁ DNA content and LDH release. These results indicate that the downregulation of Bcl-2 plays a major role in the initiation of ZD1839-induced apoptosis, and that the activation of a caspase cascade is involved in the execution of apoptosis. Furthermore, ZD1839 treatment triggered the activation of p38 mitogen-activated protein kinase (MAPK) and the down-regulation of c-Jun-N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) and phosphatidyl inositol 3-kinase (P13K)/Akt. The inhibition of the ERK and P13K/Akt pathways also significantly increased cellular death. Conclusion: ZD 1839 activated caspase-3 and the inhibited Bcl-2 in human leukemic U937 cells through the downregulation of the ERK and P13K/Akt pathways. [ABSTRACT FROM AUTHOR]