Receptor tyrosine kinases are the high affinity cell surface receptors for growth factors, cytokines and hormones. Receptor tyrosine kinases are key regulators of normal cellular processes and also play critical roles in the development and progression of many types of cancer.

Three major classes of non-receptor (cytoplasmic) tyrosine kinases have been identified: Src, Abl and Jak. Many of the non-receptor tyrosine kinases are involved in the mediation of immune and inflammatory responses, and misregulation of these enzymes has been linked to multiple human cancers.

Lipid kinases are one of the most promising new classes of potential drug targets. PI-3 and sphingosine kinases regulate a wide variety of cellular functions, including cell growth, proliferation, differentiation, intracellular trafficking, motility, and survival. As a result, defects in lipid kinase function lead to multiple disease states, including several forms of cancer and diabetes.

Serine/threonine protein kinases phosphorylate the OH group of specific serine or threonine residues. Over 125 different human serine/threonine kinases have been identified. The proteins are involved in the regulation of nearly every cell signaling pathway, including gene expression, growth, proliferation, differentiation, adhesion, motility, and death.