What is the primary mechanism of action for imatinib?

Imatinib is primarily known for its action as a BCR-ABL inhibitor. This mechanism is particularly significant because BCR-ABL is a fusion protein created by the Philadelphia chromosome, which results from the translocation of chromosomes 9 and 22. This fusion protein is constitutively active and promotes cell proliferation and inhibits apoptosis, contributing to the development of chronic myeloid leukemia (CML) and some other types of leukemia.

By specifically targeting the BCR-ABL tyrosine kinase, imatinib effectively blocks the signaling pathways that lead to malignant cell growth. This targeted inhibition is what distinguishes imatinib as a crucial therapeutic agent in the treatment of CML and also in gastrointestinal stromal tumors (GISTs) that harbor specific mutations. Therefore, the primary mechanism of action that defines imatinib's clinical utility is its ability to inhibit the BCR-ABL fusion protein, leading to reduced proliferation of abnormal cells and improved patient outcomes.