BCR-ABL (also AKT, c-Kit, ERK)

Class

Small molecule tyrosine kinase inhibitor (third-generation)

Pathway

BCR-ABL fusion kinase signaling, including the T315I gatekeeper-mutant form

BCR-ABL is an abnormal fusion protein created when parts of the BCR and ABL1 genes join together, most often in chronic myeloid leukemia and some acute lymphoblastic leukemias. This fusion produces a tyrosine kinase enzyme that is permanently switched on, driving continuous proliferation and survival signals in blood-forming cells through downstream pathways including AKT and ERK. Because BCR-ABL activity is the central driver of these leukemias, blocking its kinase function became a foundational strategy in oncology, giving rise to a class of small-molecule tyrosine kinase inhibitors (TKIs) that occupy the enzyme's ATP-binding pocket and prevent it from adding phosphate groups to downstream substrates. Over time, leukemic cells can acquire mutations in the BCR-ABL kinase domain, including the T315I 'gatekeeper' mutation, that block earlier-generation inhibitors from binding effectively. Third-generation TKIs are designed with structural features that accommodate or circumvent this mutation, restoring inhibitory activity. Some of these agents also inhibit related kinases such as c-Kit, reflecting shared structural features across the kinase family rather than a deliberate broadening of intent. This mechanism matters wherever a single dominant kinase driver sustains malignant cell growth, making kinase inhibition a rational and durable therapeutic principle.