Imatinib
Imatinib mesylate
The "magic bullet" that turned a fatal leukaemia into a manageable chronic condition.
The drug that turned a death sentence into a manageable condition.
Key Facts
- 1First rationally designed targeted cancer therapy, approved by the FDA in record time (2.5 months)
- 2Transformed chronic myeloid leukaemia (CML) from a median 3-5 year survival to near-normal life expectancy
- 3Targets the BCR-ABL fusion protein, a constitutively active tyrosine kinase found only in CML cells
- 4Five-year survival improved from ~30% to over 90% in chronic-phase CML
- 5Proved that understanding a cancer's molecular driver could lead to a precisely targeted cure
The Problem
Why This Molecule Was Needed
Chronic myeloid leukaemia (CML) is caused by a specific chromosomal abnormality: the Philadelphia chromosome, a reciprocal translocation between chromosomes 9 and 22 that creates the BCR-ABL fusion gene. The resulting BCR-ABL protein is a constitutively active tyrosine kinase that drives uncontrolled proliferation of white blood cells. By the late 1990s, interferon-alpha plus cytarabine was the standard treatment, but it was toxic, poorly tolerated, and only delayed disease progression. The only cure was an allogeneic bone marrow transplant, available to fewer than 30% of patients and carrying significant mortality risk.
Brian Druker at Oregon Health & Science University championed the idea that a small molecule specifically blocking BCR-ABL kinase activity could selectively kill CML cells while sparing normal cells. The concept was considered radical at the time: most oncologists believed kinase inhibitors would be too toxic because kinases are involved in so many normal cellular processes. Druker collaborated with Nicholas Lydon at what was then Ciba-Geigy (later Novartis) to identify a selective inhibitor from their kinase library.
The Discovery
How It Happened
The Philadelphia chromosome discovered
Peter Nowell and David Hungerford identify an abnormally small chromosome 22 in CML patients, the first chromosomal abnormality linked to a specific cancer.
CGP 57148B identified at Ciba-Geigy
Medicinal chemist Jurg Zimmermann synthesises a 2-phenylaminopyrimidine compound (later named imatinib) that inhibits BCR-ABL with an IC50 of ~25 nM.
Druker proves the concept in cell lines
Brian Druker demonstrates that CGP 57148B selectively kills BCR-ABL-positive cell lines while sparing normal haematopoietic cells, providing the crucial preclinical validation.
Phase I trial: extraordinary responses
The first-in-human Phase I trial shows complete haematological responses in 53 of 54 chronic-phase CML patients at doses above 300 mg/day, with minimal serious side effects.
Record-time FDA approval
The FDA approves imatinib for CML in just 2.5 months from submission, the fastest oncology approval at that time. The IRIS trial will later show 95% major cytogenetic response rates.
The Molecule
Up Close
Tap any region or group card to explore key structural features.
The Takeaway
Targeting the inactive kinase conformation for selectivity
Imatinib proved that rational targeting of a single oncogenic driver could transform an aggressive cancer into a chronic, manageable disease. Its key molecular trick was binding the inactive DFG-out conformation of ABL kinase, a conformational state that differs more between kinases than the active state does. This selectivity strategy has since guided the design of dozens of kinase inhibitors across oncology.
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