Breakpoint cluster region–ABL1 fusion protein (BCR–ABL1) (BCR–ABL1)

The Breakpoint cluster region–ABL1 fusion protein (BCR–ABL1) is an oncogenic, constitutively active tyrosine kinase generated by the Philadelphia chromosome translocation t(9;22), fusing the N-terminal BCR region to the ABL1 kinase domain. Distinct breakpoint combinations produce different fusion transcripts and proteins: p210 BCR–ABL1 (b2a2 or b3a2) typical of chronic myeloid leukemia, p190 BCR–ABL1 (e1a2) frequent in Philadelphia-positive B-cell acute lymphoblastic leukemia, and the rarer p230 BCR–ABL1 (e19a2) in chronic neutrophilic leukemia. Oligomerization mediated by the N-terminal BCR coiled-coil activates ABL1 kinase and influences cytoskeletal interactions and transformation, contributing to leukemogenesis. BCR–ABL1 is a validated therapeutic target; multiple tyrosine kinase inhibitors (TKIs) that bind the ATP site, and the allosteric inhibitor asciminib that binds the myristoyl pocket, achieve disease control, though resistance arises via kinase domain mutations (notably in the P-loop and the T315I “gatekeeper”), guiding drug selection and combination strategies.

Other names

BCR-ABLBCR::ABLPhiladelphia chromosome fusion proteinp190 BCR–ABL1 (e1a2)p210 BCR–ABL1 (b2a2 or b3a2)p230 BCR–ABL1 (e19a2)

ATP-competitive inhibition of the ABL1 tyrosine kinase domain (e.g., imatinib, dasatinib, nilotinib, bosutinib, ponatinib) Allosteric inhibition via myristoyl pocket binding that locks ABL1 into an inactive conformation (e.g., asciminib; “STAMP” mechanism) Combination allosteric plus ATP-site dual targeting to overcome resistance (strategy described for resistant mutants)