The cell cycle.
July 9, 2009 The cell cycle No Comments
An understanding of the normal cell cycle and the behavior of malignant or cancerous cells can help one better understand how chemotherapy works to destroy cancer cells. The cell cycle is the sequence of steps a cell goes through in order to copy its genetic material and divide into two cells. The cell cycle is divided into four phases: the G 1, S, G 2, and M phases. A chemotherapy agent may work in only one phase of the cycle (called cell-cycle specific) or be active in all phases (cell-cycle nonspecific).
The G 1 phase is the phase most active in protein synthesis. The cellular DNA at this phase is tightly coiled and is not actively being transcribed (copied). Few chemotherapy agents are active at this phase of the cell cycle. By contrast, the S phase is the synthetic phase of the cell cycle. DNA replication is most active in this phase and many chemotherapy agents work in this phase. G 2 represents a time when mostly RNA (and some protein) is actively produced. Mitosis, or actual cell division, occurs during the M phase. There are two major classes of chemotherapy drugs that are most active during this phase of the cell cycle. By knowing the phase an agent works in, we are able to combine agents that work in different phases to achieve the most tumor killing.