Expression of apoptosis proteins in chronic myelogenous leukemia - Associations and significance

BACKGROUND, The mechanisms favoring the growth advantage of Philadelphia ch romosome positive cells over normal cells in chronic myelogenous leukemia ( CML) are not fully elucidated but could be due partly to altered apoptosis and longer survival of CML clones. Also, little is known about the biologic characteristics of disease progression in CML. Bcl-2 expression has been d emonstrated to exert an antiapoptotic effect resulting in increased cell su rvival. Other proteins such as Bax and Bad are proapoptotic proteins. Fas, a cell surface protein, can be triggered by an appropriate death-promoting ligand (FasL) to activate downstream caspases pivotal in initiation of prog rammed cell death. Although the mechanisms underlying cellular proliferativ e and apoptotic pathways are complex, with involvement of multiple interloc king proteins, the relative expression of pro- and antiapoptotic proteins m ay have an influence on disease progression. This study aimed to determine whether the changes in the cellular expression of Bcl-2, Bax, and Fas corre late with caspase-3 activity and disease progression in CML, or with respon se to interferon (IFN)-alpha therapy and prognosis in early chronic phase C ML. METHODS. Bcl-2, Bax, and Fas expression were measured on whole cell lysates from bone marrow mononuclear cell fractions by Western blot analysis and q uantitative radioimmunoassay. Caspase-3 activity was determined using the D EVD system. Specimens from 203 patients with CML were examined. These inclu ded 130 patients in early chronic phase disease (ECP; diagnosis to therapy, less than or equal to 12 months), 33 patients in late chronic phase (diagn osis to therapy, > 12 months), 27 patients in accelerated phase, and 13 pat ients in blastic phase. Correlations between apoptosis proteins and CML pha ses, risk groups in ECP, and response to IFN-alpha therapy and survival in ECP were investigated by standard statistical methods, and positive finding s were assessed by multivariate analysis. RESULTS. Levels of Bcl-2, Fas, Bax, and caspase-3 activity did not correlat e with disease progression. Among patients in ECP, higher Fas levels correl ated with poorer risk groups (P = 0.05) and higher caspase-3 activity corre lated with better risk groups (P = 0.048). With IFN-alpha therapy, major cy togenetic responses were noted in 30% of patients with high Fas and 53% wit h low Fas (P = 0.016) and failure to achieve a complete hematologic respons e (CHR) in 25% versus 2% (P = 0.0001). Survival was shorter with high Fas l evels (5-year rates, 71% vs. 52%; P = 0.002), and the independent poor prog nostic significance of high Fas levels was confirmed by multivariate analys is (P = 0.014). Response to IFN-alpha: therapy and survival were not signif icantly different by different levels of Bcl-2, Bax, or caspase-3 activity. CONCLUSIONS. High Fas levels were associated with intrinsically worse disea se at diagnosis, whereas high caspase-3 activity was associated with good r isk disease. In ECP CML, high Fas levels were associated with significantly worse response to IFN-alpha therapy and with significantly worse survival. The influence of these cellular proteins and caspase-3 activity on apoptos is in CML is complex and merits further investigation. Cancer 2001;91:1964- 72. (C) 2001 American Cancer Society.