Malignancy: Subsequential Alterations of Telomeric DNA Length Correlate with Cytogenetic Response in Chronic Myeloid Leukemia Treated with Interferon alpha

Telomere Biology of Human Hematopoietic Stem Cells

BACKGROUND

Telomeres are protein DNA structures present at the ends of chromosomes and are essential for genetic stability and cell replication. Telomerase is the enzyme complex that maintains telomere integrity. Hematopoietic stem cells express telomerase and contain long telomeres, which become shorter as cells differentiate and mature. The extent of telomere shortening and the level of telomerase activity often correlate with the presence and severity of some hematopoietic diseases.

METHODS

The fundamentals of telomeres and telomerase are reviewed, and the telomere biology of human hematopoietic cells is discussed.

RESULTS

Telomere length and telomerase activity are important in the self-renewal of hematopoietic stem cells. Changes within these compartments affect both normal hematopoietic cells and the generation of hematopoietic disease. Telomere length provides information pertaining to the proliferative history and potential of a hematopoietic cell.

CONCLUSIONS

The role of telomerase and telomeres within the hematopoietic compartment needs further clarification. Advances in our knowledge in this field may improve clinical outcomes for the treatment of hematologic disease.

Increased telomerase activity is associated with shorter survival in patients with chronic phase chronic myeloid leukemia

BACKGROUND

Significantly elevated telomerase activity (TA) has been found in samples from patients with many malignant hematologic diseases. However, the impact of elevated TA on the course of patients with chronic phase chronic myeloid leukemia (CP-CML) is unknown.

METHODS

Using a modified polymerase chain reaction-based telomeric repeat amplification protocol assay, the authors measured TA in bone marrow samples from 93 patients with CP-CML and correlated it with patient characteristics and survival. TA also was measured in bone marrow samples from 29 patients with accelerated/blastic phase CML.

RESULTS

Patients with accelerated/blastic phase CML were found to have somewhat higher levels of TA compared with patients with CP-CML (P = 0.07). Among patients with CP-CML, those with high TA progressed to advanced stages of disease sooner (P = 0.05) and had a significantly shorter survival (P = 0.04) than patients with low TA. No correlation was found between TA and patient age, hemoglobin, platelet and leukocyte counts, percentage of peripheral or bone marrow blasts or basophils, or bone marrow cellularity. On multivariate analysis, high TA retained its significance as a factor associated with shorter patient survival (P = 0.02).

CONCLUSIONS

The current study data suggest that TA plays a role in the propagation of CP-CML and that the potential of telomerase inhibitors in patients with CML should be explored, even in those with early phase disease.

Telomere dynamics and genetic instability in disease progression of chronic myeloid leukemia

Chronic myeloid leukemia (CML) is characterized by a Philadelphia (Ph) translocation creating a novel BCR-ABL oncoprotein, and CML patients have a chronic phase for several years followed by an intractable blast cell proliferation, called blast transformation. In the blast phase, more than 60% of patients show additional cytogenetic changes, e. g., double Ph, +8, i(17q). In this review, we would like to address genetic changes, including genome instability, cytogenetic changes, and telomere dynamics that relate to karyotypic instability. In the chronic phase, approximately 60% of CML patients show reduced telomere length without highly elevated telomerase activity or microsatellite alterations, indicating that telomere reduction may be linked to cell replication. Therefore, the Ph translocation might be a first event to immortalize cell proliferation. In the blast phase, 50% of CML patients have high levels of elevated telomerase activity and the same number of patients had microsatellite changes. Of note is that most patients with telomerase up-regulation in the blast phase had additional cytogenetic changes and >60% of them showed microsatellite changes at least at one locus. In contrast, most patients without telomerase activity did not show microsatellite changes. These findings may indicate that telomerase up-regulation in the blast phase of CML patients is closely associated with microsatellite changes (representative of genome instability), while blast cells in the remaining patients (30%) maintain their proliferative capability without microsatellite changes and telomerase up-regulation. This further suggests that there is also an unknown mechanism for genome stability without the process of telomerase up-regulation in some patients with CML in blast crisis.