Expression of Bcl-2 protein and the amplification of c-myc gene in patients with chronic myeloid leukemia

Second generation tyrosine kinase inhibitors prevent disease progression in high-risk (high CIP2A) chronic myeloid leukaemia patients

High cancerous inhibitor of PP2A (CIP2A) protein levels at diagnosis of chronic myeloid leukaemia (CML) are predictive of disease progression in imatinib-treated patients. It is not known whether this is true in patients treated with second generation tyrosine kinase inhibitors (2G TKI) from diagnosis, and whether 2G TKIs modulate the CIP2A pathway. Here, we show that patients with high diagnostic CIP2A levels who receive a 2G TKI do not progress, unlike those treated with imatinib (P=<0.0001). 2G TKIs induce more potent suppression of CIP2A and c-Myc than imatinib. The transcription factor E2F1 is elevated in high CIP2A patients and following 1 month of in vivo treatment 2G TKIs suppress E2F1 and reduce CIP2A; these effects are not seen with imatinib. Silencing of CIP2A, c-Myc or E2F1 in K562 cells or CML CD34+ cells reactivates PP2A leading to BCR-ABL suppression. CIP2A increases proliferation and this is only reduced by 2G TKIs. Patients with high CIP2A levels should be offered 2G TKI treatment in preference to imatinib. 2G TKIs disrupt the CIP2A/c-Myc/E2F1 positive feedback loop, leading to lower disease progression risk. The data supports the view that CIP2A inhibits PP2Ac, stabilising E2F1, creating a CIP2A/c-Myc/E2F1 positive feedback loop, which imatinib cannot overcome.

Programmed cell death proteins and chronic leukemia

Apoptosis or programmed cell death is a genetically regulated process of cellular suicide. Apoptosis has been implicated in a wide range of pathological conditions, and mutations in apoptotic genes play important roles in the process of malignant transformation. Chronic leukemia represents a neoplastic disorder caused primarily by defective programmed cell death, as opposed to increased cell proliferation. This paper presents the main results of our ten-year research on the apoptosis of leukemia cells. The research included the morphological aspects of the process, the effect of antineoplastic agents on the induction of apoptosis in leukemia cells and expression analysis of the proteins involved in programmed cell death. Special attention was paid to the expression and interaction of the Bcl-2 family of proteins in leukemia cells. The ultimate aim of the study of apoptosis of leukemic cells is the discovery of new biological agents that might be used in the treatment of chronic leukemia.