Palbociclib, sold under the brand name Ibrance among others, is a medication developed by Pfizer for the treatment of HR-positive and HER2-negative breast cancer. See also Palbociclib. It is a selective inhibitor of the cyclin-dependent kinases CDK4 and CDK6 (see also CDK4).[1][2]
In the G1 phase of the cell cycle, mammalian cells must pass a checkpoint, known as the restriction point "R", in order to complete the cell cycle and divide. CDK4 and CDK6 complex with cyclin D drive the phosphorylation of the retinoblastoma protein, Rb, which allows the cell to pass R and commit to division. Regulation of one or more proteins involved in this checkpoint is lost in many cancers. However, by inhibiting CDK4/6, palbociclib ensures that the cyclin D-CDK4/6 complex cannot aid in phosphorylating Rb. This prevents the cell from passing R and exiting G1, and in turn from proceeding through the cell cycle.[3]
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