New treatment for chronic eosinophilic leukemia

May 10 2006

Leukemia - or cancer of the bone marrow - strikes some 700 Belgians each year. Chronic Eosinophilic Leukemia (CEL), a specific form of leukemia, is currently treated with Glivec.

However, recent research has shown that prolonged usage can cause resistance to Glivec, rendering this chronic form of leukemia untreatable. Researchers from the Flanders Interuniversity Institute for Biotechnology (VIB) connected to the Catholic University of Leuven have now discovered that another drug, Sorafenib (Nexavar), works on patients that have developed this resistance. This finding is not only important for CEL patients, but it also provides a new approach for treating specific forms of leukemia. It is clear from this research that a combination of targeted drugs provides a greater chance of lifelong effective treatment.

Our body's white blood cells combat foreign intruders (such as viruses and bacteria). However, in chronic leukemia, the cells in the bone marrow that should develop into white blood cells multiply uncontrollably. These blood cells do not function properly, jeopardizing the production of normal blood cells. Among other consequences, this makes patients more susceptible to infections. Chronic leukemia appears in several forms - in CEL, a rare form of leukemia, the excessive increase of eosinophils (a certain type of white blood cell) can cause tissue damage in the heart, the skin, and the central nervous system.

Under normal circumstances, our body regulates the production of white blood cells very precisely by means of a targeted activation of tyrosine kinases, which start this production. But sometimes defects in the DNA cause these tyrosine kinases to be active continuously, giving rise to diseases like leukemia. In 2003, Jan Cools and his colleagues under the direction of Peter Marynen, along with colleagues Elizabeth Stover and Gary Gilliland from Boston, discovered that CEL is caused by this kind of defective activation of the tyrosine kinase FIP1L1-PDGFRa. Now, with additional research, they have uncovered the molecular mechanism behind the abnormal activation of FIP1L1-PDGFRa. This new research is being published this week on the website of the scientific journal PNAS.

In the fight against CEL (and other forms of leukemia), scientists use proteins that inhibit the tyrosine kinases. Glivec is such an inhibitor and is effective against CEL because it specifically inhibits the activity of FIP1L1-PDGFRa. However, CEL patients must take Glivec every day for the rest of their lives - and recent research shows that, over time, alterations in the DNA can arise, causing resistance to Glivec. The longer Glivec is taken, the greater the chance resistance will develop. At that point, treatment with Glivec is no longer effective.

This problem prompted VIB researchers Els Lierman and Jan Cools to look for alternatives. They have found that Sorafenib, another inhibitor, works effectively in treating the resistant form of CEL. Sorafenib is already on the market in the US as a remedy for kidney tumors. This new research indicates that, to be able to treat certain forms of leukemia (like CEL) effectively over a long period of time, several inhibitors must be used, either together or successively. The scientists emphasize the importance of testing known inhibitors for their effectiveness against CEL and other forms of leukemia. This research has recently appeared in the scientific journal Blood.