Overexpression of the Anti-Apoptotic Genes mcl-1, bcl-w, bcl-x_L and a1 Is Correlated with Chronic Myelogenous Leukemia Progression and Resistance to Gleevec.

Chronic myeloid leukemia (CML) is a stem cell disease where t(9;22) translocation is considered the primary molecular event leading to the appearance of the bcr-abl fusion gene and consequent cellular transformation. Bcr-Abl tyrosine-kinase inhibitors have been developed and are fairly successful in the treatment of CML. Despite their outstanding clinical activity in CML, they are not a definitive cure: the efficacy of imatinib mesylate (Gleevec®), for instance, in CML-blastic phase is reduced and reports of resistance and intolerance to it have been published. Since Bcr-abl initiates cellular modifications leading to an extreme resistance to apoptosis, we decided to investigate possible secondary targets for CML therapy. We evaluate the expression of known anti and pro-apoptotic genes in terms of CML progression and response to Gleevec. We studied 10 health controls and 71 CML patients in different phases (20 chronic phase, 20 accelerated phase, 10 blastic phase, 15 cytogenetic remission post-Gleevec® and 6 Gleevec® refractory patients). CML group was constituted by 26 men and 35 women, median age of 51.7 years (range 23–73 years), 5 men and 5 women, median age of 49.3 (range 25–72 years), were healthy controls. Peripheral blood mononuclear cells were isolated and expression of bax, bcl-w, mcl-1, bcl-2, a1 and bcl-x_L was analyzed by real-time RT-PCR. Protein expression of Bcl-2 and Bcl-x_L were analyzed by western-blot. The results of real-time RT-PCR and western-blot are expressed by relative expression, e.g. ratio of investigated genes or protein to the reference GAPDH gene and protein, respectively. We observed an increase of bcl-w (p<0.001), mcl-1 (p< 0.001), a1 (p<0.01) and bcl-x_L (p<0.001) gene expression and a remarkable reduction of bcl-2 (p<0.001) in CML-BP patients (table 1). Patients in remission post-Gleevec® presented an anti-apoptotic gene expression profile similar to controls (p>0.05) and refractory patients profile seem to be analogous to blastic crisis (p>0.05). bax levels did not show significant changes in CML patients in different phases (p>0.05). Bcl-2 and Bcl-x_L protein data support real-time RT-PCR findings. Taken together these results suggest that mcl-1, bcl-w, bcl-x_L and a1 contribute to disease progression and resistance to treatment in CML patients. Further investigations on the state of the apototic machinery in CML patients should provide new approaches for drug design and consequently new efficient treatment for AP, BC and refractory CML patients.