Imatinib

Imatinib (INN), marketed by Novartis as Gleevec (Canada, South Africa and the USA) or Glivec (Australia, Europe and Latin America), and sometimes referred to by its investigational name STI-571, is a tyrosine-kinase inhibitor used in the treatment of multiple cancers, most notably Philadelphia chromosome-positive (Ph⁺) chronic myelogenous leukemia (CML).

In order to survive, cells need signaling through proteins (signal cascade) to keep them alive. Some of the proteins in this cascade use a phosphate group as an "on" switch. This phosphate group is added by a tyrosine kinase enzyme. In healthy cells, these tyrosine kinase enzymes are turned on and off as needed. In Ph-positive CML cells, one tyrosine kinase enzyme, BCR-Abl, is stuck on the "on" position, and keeps adding phosphate groups. Imatinib blocks this BCR-Abl enzyme, and stops it from adding phosphate groups. As a result, these cells stop growing, and even die by a process of cell death (apoptosis). Because the BCR-Abl tyrosine kinase enzyme exists only in cancer cells and not in healthy cells, imatinib works as a form of targeted therapy—only cancer cells are killed through the drug's action. In this regard, imatinib was one of the first cancer therapies to show the potential for such targeted action, and is often cited as a paradigm for research in cancer therapeutics.