Protein kinase inhibitor belongs to a type of enzyme inhibitor, which can block the protein kinase action. Protein kinase can add a phosphate group to proteins, called phosphorylation, which can change their activity and function. Phosphorylation is often a necessary step in some cancers and inflammatory disorders. Protein kinase can regulate the whole process of neoplasia, including proliferation, invasion, angiogenesis and metastasis. Inhibiting the phosphorylation process of the protein kinase can treat many type of cancers. In order to inhibit the process of phosphorylation amino acid, kinases mainly act on serine and threonine kinase. Studies show that tyrosine kinase acts on tyrosine only. There are some dual-specificity kinases acting on three amino acid residues, including serine, threonine or tyrosine kinase. Several protein kinases also phosphorylate other amino acids. For example, histidine kinases act on histidine residues. Protein kinase inhibitors can be classified according to the amino acid on a protein that added to the protein kinase. Therefore, protein kinase inhibitor has been used in clinical trials and developed in drug research, such as imatinib, Lapatinib, Nilotinib and so on.
A protein kinase is an enzyme that modifies proteins by transferring a phosphate group from ATP. Protein kinases play important roles in regulating most cellular functions. Protein kinases act on the amino acids serine, threonine, and tyrosine. A protein kinase inhibitor is a compound that blocks the action of one or more protein kinases. Therefore, molecules that can inhibit the activity of protein kinases, protein kinase inhibitors (PKI), can be used both in investigating the function of a specific kinase in a particular signalling pathway, as well as in preventing the aberrant action of protein kinases in pathophysiological conditions.
Protein kinase inhibitors can be subdivided according to the amino acid on a protein that they add the phosphate to (e.g serine, threonine or tyrosine) in order to inhibit phosphorylation of that amino acid. Kinases mostly act on both serine and threonine, but tyrosine kinase acts on tyrosine only and some dual-specificity kinases act on all three of these amino acid residues. Some protein kinases also phosphorylate other amino acids, such as histidine kinases that act on histidine residues.