Low BCR-ABL expression levels in hematopoietic precursor cells enable persistence of chronic myeloid leukemia under...

Area of Science:

• Hematology
• Oncology
• Molecular Biology

Background:

• Imatinib mesylate (IM) is a tyrosine kinase inhibitor used to treat chronic myeloid leukemia (CML).
• BCR-ABL overexpression and stem cell quiescence are implicated in IM treatment failure.
• The behavior of BCR-ABL expression in persisting CML cells during long-term therapy remains unclear.

Purpose of the Study:

• To investigate BCR-ABL expression levels in persisting CML precursors during major molecular remission (MMR).
• To assess the impact of long-term IM therapy on CML cell clearance in bone marrow compartments.
• To determine the relationship between BCR-ABL expression levels and IM sensitivity.

Main Methods:

• Quantification of BCR-ABL-positive precursors in bone marrow compartments during MMR.
• Comparison of BCR-ABL expression levels in colony-forming units (CFUs) at diagnosis versus MMR.
• In vitro assessment of IM sensitivity in murine bone marrow cells engineered with varying BCR-ABL expression levels.

Main Results:

• BCR-ABL-positive precursor numbers significantly decreased across all bone marrow compartments during MMR.
• Persisting MMR CFUs exhibited substantially lower BCR-ABL expression compared to diagnostic CML CFUs.
• Murine cells with low BCR-ABL expression showed reduced sensitivity to IM compared to those with high expression.

Conclusions:

• Major molecular remission in CML is characterized by the persistence of clones with low BCR-ABL expression.
• Low BCR-ABL levels may confer insensitivity to imatinib mesylate.
• These findings suggest potential implications for optimizing residual disease management strategies in CML.