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Protein Block
A promising weapon against blood
cancer is a
drug called STI-571, reports Biplab Das
An effective drug for leukaemia is hard to come by. The drugs developed till now have failed to provide a cure. Now, a research team comprising John Kuriyan and Thomas Schindler of the Rockfeller University, New York City has found a compound called STI-571, which seems able to combat chronic myelogenous leukaemia (CML).
In a recent issue of Science, the Rockfeller team wrote that STI-571 blocks an enzyme produced by a cancer-causing gene called ab1. In CML patients, ab1 triggers the massive production of leukaemia cells, acting through a protein called Ab1. Experiments showed that STI-571 inhibits Ab1, which acts as a receptor for platelet derived growth factor (PDGF). PDGF causes increased production of leukaemia cells. STI-571 cuts off the communication between ab1 and PDGF, thereby halting the unbridled growth of cancer cells.
The Rockfeller team has also identified the defective chromosomes suspected of causing CML. A portion of chromosome 22 carrying a gene called bcr merges with the segment of chromosome 9 carrying ab1. This merger produces a hybrid protein called Bcr-Ab1, which causes leukaemia.
Another group led by Brian Druker at the Oregon Health Sciences University, Portland, has also had encouraging results in clinical trials of STI-571. Druker revealed them at a recent meeting of the American Society of
Haematology. When patients resistant to another anti-cancer drug called interferon L were given STI-571, the number of their cancer cells reduced to a great extent.
In a follow-up after a year, Druker found that 30 recipients of STI-571 showed gradual regression of cancer cells.
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3 WAYS TO IDENTIFY
CHRONIC LEUKAEMIA
1) Physical symptoms: Initially the patient may show no signs of disease. But fatigue,
anaemia, weight loss and pain in the spleen occur eventually. The spleen is abnormally enlarged, with a splenic notch palpable. Peptic ulceration is common. Retinal haemorrhages are also encountered.
2) Clinical findings: The diagnosis can be made from blood film examination. The white blood count is grossly elevated. A variable degree of
anaemia is observed and platelet count may be high. Excess production of abnormal platelets is because of the enlarged spleen. Bone marrow examination, though usually performed, does not contribute to detection of
CML. Chromosome abnormality, the cause of CML, can be detected in cultured marrow cells.
3) Progress of CML: As the cancer progresses, the spleen enlarges and the patient becomes more
anaemic. The white blood count doubles every 3-12 months. It may fluctuate, depending on the patient's response to treatment, and a plateau is reached when the patient
stabilises. When the disease is in an aggressive and drug-resistant state, splenomegaly (enlarged spleen) develops. |
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