Ribociclib

Ribociclib, sold under the brand name Kisqali, is a medication used for the treatment of certain kinds of breast cancer. Ribociclib inhibits the enzymes cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6).^[1] See also Ribociclib and CDK4.

Cyclin-dependent kinases (CDKs) 4 and 6 are enzymes that have been shown to promote cell division and multiplication in both normal and cancer cells. Many cancer cells have shown abnormalities that increase the activity of CDK, leading to the inactivation of certain tumor suppressor genes.^[2][3]

When used in combination with other drugs such as an anaplastic lymphoma kinase ALK or an MEK inhibitor, ribociclib has been shown to have a synergistic effect, resulting in improved responses.^[4][5] Again, this is likely a result of "crosstalk" between signaling pathways. Simply blocking one pathway in cancer tumorigenesis can sometimes result in "tumor compensation", where the tumor compensates for the blocked signaling pathway by utilizing other pathways to survive. By blocking several pathways at once, it is thought that the tumor is less able to compensate, and a greater anti-tumor response is often observed. Utilizing ribociclib in combination with other agents has been shown to reduce the development of resistance to these agents.^[2]