Short answers, pulled from the story.
The cell cycle is a sequential series of events that causes a single cell to grow, duplicate its DNA, and divide into two daughter cells. This process ensures the survival of organisms ranging from the simplest bacteria to the most complex humans. It operates as the silent engine that drives every heartbeat, every breath, and every thought.
In eukaryotic cells, the process is divided into two main stages: interphase and the M phase. Interphase includes the G1 phase, S phase, and G2 phase, while the M phase consists of mitosis and cytokinesis. Interphase represents the phase between two successive M phases and lasts for at least 91% of the total time required for the cell cycle.
Leland H. Hartwell, R. Timothy Hunt, and Paul M. Nurse won the 2001 Nobel Prize in Physiology or Medicine for their discovery of central molecules that control the cell cycle. These molecules include cyclins and cyclin-dependent kinases, which determine a cell's progress through the cycle.
Cyclin D binds to existing CDK4/6 to form the active cyclin D-CDK4/6 complex, which phosphorylates the retinoblastoma susceptibility protein Rb. This phosphorylation triggers the dissociation of pRB-E2F complexes, thereby inducing G1/S cell cycle gene expression and progression into the S phase.
Three main checkpoints exist to ensure that damaged or incomplete DNA is not passed on to daughter cells: the G1/S checkpoint, the G2/M checkpoint, and the metaphase checkpoint. The G1/S checkpoint is also known as the restriction point, and the G2/M checkpoint ensures the cell has enough cytoplasm and phospholipids for two daughter cells.
Three Cdk4/6 inhibitors, palbociclib, ribociclib, and abemaciclib, currently received FDA approval for clinical use to treat advanced-stage or metastatic, hormone-receptor-positive, HR-positive, HER2-negative breast cancer. These inhibitors prevent a malignant tumor from proliferating by targeting Cdk4/6, which is characterized to be a therapeutic target for anti-tumor effectiveness.