Tyrosine Kinase Update: Role and Response in Cancer Therapy

For the past several decades, the understanding of the molecular mechanisms of cancer initiation, progression, and metastasis has increased. As data elucidating these mechanisms has been amassed, potential targets for therapy have been identified. Tyrosine kinases were first recognized in 1979 and subsequently their potential role in cancer has been established. There are approximately 90 known tyrosine kinases in human cells, about half of which are receptor tyrosine kinases. The receptor tyrosine kinases span the cell membrane and are activated by binding of a ligand. Cytoplasmic nonreceptor tyrosine kinases, or intracellular tyrosine kinases, are downstream of receptor tyrosine kinases. The receptor tyrosine kinases act in concert with intracellular tyrosine kinases to mediate cell behaviors, including growth and proliferation, angiogenesis, apoptosis, gene transcription, and intercellular interactions. Inappropriate activation of tyrosine kinases plays a significant role in the initiation and progression of human cancers. The critical role of tyrosine kinases in signal transduction, coupled with the frequent incidence of their increased expression levels and activating gene mutations in cancer, makes these enzymes attractive targets for therapeutic intervention in cancer treatment. This article provides a summary of current drugs targeting tyrosine kinases for cancer therapy, focusing on those being used in the clinic. Keywords: Tyrosine kinases, cancer therapy, Src homology, scaffolding protein, immunohistochemistry, bevacizumab, Lapatinib, antisense oligonucleotides