Bcr-Abl tyrosine-kinase inhibitor

Bcr-Abl tyrosine-kinase inhibitors (TKI) are the first-line therapy for most patients with chronic myelogenous leukemia (CML). More than 90% of CML cases are caused by a chromosomal abnormality that results in the formation of a so-called Philadelphia chromosome. This abnormality was discovered by Peter Nowell in 1960 and is a consequence of fusion between the Abelson (Abl) tyrosine kinase gene at chromosome 9 and the break point cluster (Bcr) gene at chromosome 22, resulting in a chimeric oncogene (Bcr-Abl) and a constitutively active Bcr-Abl tyrosine kinase that has been implicated in the pathogenesis of CML. Compounds have been developed to selectively inhibit the tyrosine kinase.

Before the 2001 U.S. Food and Drug Administration (FDA) approval of imatinib, no drugs were available to alter the natural progression of CML. Only cytotoxic drugs such as busulfan, hydroxyurea or interferon-alpha (rIFN-α) were utilized. Even though the first Bcr-Abl TK inhibitor was named “the magic bullet” to cure cancer by TIME magazine, a second generation of Bcr-Abl TKI was subsequently developed to combat the initial resistance that emerged.

New forms of resistance can arise as: missense mutations within the Abl kinase domain, over-expression of Bcr-Abl, increased production of transmembrane plasma proteins, or the constitutive activation of downstream signaling molecules such as Src-family kinases.

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