Which medication is commonly used to treat leukemia by blocking signals in leukemic cells?

• A. Imatinib mesylate (Gleevec)
• B. Vincristine
• C. Doxorubicin
• D. Bleomycin

Answer: (A)

Blocking abnormal signaling inside leukemic cells is a targeted therapy approach, illustrated by imatinib. In leukemias like CML, the BCR-ABL fusion protein has continuous tyrosine kinase activity that drives uncontrolled cell growth. Imatinib binds to the ATP-binding site of BCR-ABL, inhibiting its kinase activity and thus stopping the downstream signaling that promotes proliferation. With those signals blocked, leukemic cells stop dividing and are more likely to die, while healthier cells are relatively spared.

The other drugs work through different mechanisms: vincristine disrupts microtubule formation to halt cell division, while doxorubicin and bleomycin damage DNA rather than blocking signaling pathways.