Introduction to TKIs
Tyrosine kinase inhibitors are small molecules that are effective in the treatment of a wide variety of cancers. Here, we review tyrosine kinase inhibitors pharmacology – covering indications, mechanism of action, key adverse effects, and other important clinical pharmacology that you need to know.
Tyrosine kinases are enzymes that belong to the family of protein kinases. They phosphorylate the cell by transferring the phosphate group from ATP to cell proteins and hence regulates signal transduction and intracellular signaling. Tyrosine kinases are responsible for cellular activities like cell division, cell differentiation, cell migration, cell growth, cell metabolism and apoptosis in response to internal and external stimuli.
The tyrosine kinase receptors are free-floating monomers present on the cell membrane, having an intracellular and extracellular domain. The growth factor causes dimerization and activation of receptor monomers which, in turn, phosphorylates tyrosine kinase in the intracellular domain. There are many different types of tyrosine kinase receptors, the ones which are involved in anticancer effects are mainly VEGFR kinase, EGFR kinase, SRC family, Bruton tyrosine kinase, PDGFR kinase and ABL family.
All these drugs have a suffix –tinib, letting you know that they are small molecule inhibitors. We can classify tyrosine kinase inhibitors as follows:
BCR-ABL tyrosine kinase inhibitors
EGFR tyrosine kinase inhibitors
VEGF receptor tyrosine kinase inhibitors
Bruton’s tyrosine kinase inhibitors
Normally, the activity of tyrosine kinase is short and reversible due to the action of protein tyrosine phosphatases. In cancer, usually tyrosine kinases or their pathways are activated by mutation, gene amplification or chromosomal translocation, resulting in increased growth of cancerous cells. Since these pathways regulate cell proliferation, its survival, migration and angiogenesis, tyrosine kinase inhibitor medicines serve as effective weapons against cancer.
Tyrosine kinase inhibitors work by blocking the tyrosine kinase from sending chemical messages to the cells that signals them to grow. They inhibit the effects of growth factors like EGF, VEGF, PDGF and others. They stop replication of cells and the formation of new blood vessels that provide nutrition and oxygen to the cancerous cells. On the oncogenic tyrosine kinases, tyrosine kinase inhibitors compete with the ATP binding site of the catalytic domain. They interfere with specific cell signaling pathways, therefore serving as targeted therapy often with fewer adverse effects compared to previous therapies.
Lapatinib is also a tyrosine kinase inhibitor but it also targets a protein called HER2 (human epidermal growth factor receptor-2). This protein is present in large amounts in breast cancer. Since HER2 helps the cells in their growth and division, lapatinib stops the activity of HER2.
Tyrosine Kinase Inhibitors Pharmacology
|Drug||Trade name||Indications||Side effects|
Bone marrow disorders
|Congestive heart failure
Ph+ acute lymphoblastic
|Nilotinib||Tasigna||Ph+ CML||QT prolongation
Difficulty in breathing
|Gefitinib||Iressa||Non-small cell lung
Holes in the gastrointestinal tract
|Sorafenib||nexAVAR||Giant cell tumors||Severe liver injury
Edema of eye
|Vandetanib||Caprelsa||Thyroid cancer||QT prolongation
Torsades de pointes
Here are some important clinical considerations about tyrosine kinase inhibitors pharmacology that you need to know:
- Sunitinib, sorafenib, vandetanib and pazopanib metabolize through the liver by CYP 3A4. Therefore, caution should be exercised with coadministration of CYP3A4 inducers, as they may decrease the plasma concentration of tyrosine kinase inhibitors. Similarly, CYP inhibitors can increase toxicity risk.
- Antiangiogenic drugs can cause an increase in blood pressure; an important consideration for patients with hypertension and other underlying conditions.
- Nilotinib carries a black-box warning for cardiac complications – including an increased risk of QT prolongation, hypokalemia, and arrhythmias. Other drugs – such as vandetanib, sinitinib, and pazopanib, can also cause QT prolongation.
That completes our study of tyrosine kinase inhibitors pharmacology. Check back to our pharmacy blog soon for more content on TKIs and other important medicines used in the treatment of cancers.