Let’s return to our earlier look at cancer: One example of a gene modification that alters the growth rate is increased phosphorylation of cyclin B, a protein that controls the progression of a cell through the cell cycle and serves as a cell-cycle checkpoint protein.
For cells to move through each phase of the cell cycle, the cell must pass through checkpoints. This ensures that the cell has properly completed the step and has not encountered any mutation that will alter its function. Many proteins, including cyclin B, control these checkpoints. The phosphorylation of cyclin B, a post-translational event, alters its function. As a result, cells can progress through the cell cycle unimpeded, even if mutations exist in the cell and its growth should be terminated.
Cancer therapies are designed to target actively dividing cells. Besides cancer cells, what other cells actively divide in humans? One of the most physically obvious side effects of cancer treatments is hair loss. This is because the living cells in the hair root continually divide to make hair grow longer. These cells therefore are often impacted by broad scale cancer treatments like chemotherapy drugs and radiation localized to the head. Shortly after cancer treatments, a patient’s blood count may also drop. This is due to the rapid division of blood cells throughout a person’s life. Unlike hair cells though, blood cells divide fairly often and rapidly. Hence, the blood count often returns to normal much faster than hair regrows.
New Drugs to Combat Cancer: Targeted Therapies
Scientists are using what is known about the regulation of gene expression in disease states, including cancer, to develop new ways to treat and prevent disease development. Many scientists are designing drugs on the basis of the gene expression patterns within individual tumors. This idea, that therapy and medicines can be tailored to an individual, has given rise to the field of personalized medicine. With an increased understanding of gene regulation and gene function, medicines can be designed to specifically target diseased cells without harming healthy cells. Some new medicines, called targeted therapies, have exploited the overexpression of a specific protein or the mutation of a gene to develop a new medication to treat disease. One such example is the use of anti-EGF receptor medications to treat the subset of breast cancer tumors that have very high levels of the EGF protein. Undoubtedly, more targeted therapies will be developed as scientists learn more about how gene expression changes can cause cancer.
As scientists learn more about cell division and the unique ways it malfunctions in cancer cells, they are able to develop targeted therapies. These drugs are still chemotherapies, but they are often focused on a particular feature of different types of cancer cells, making them less likely to target non-cancerous dividing cells. This reduces global side effects. Unfortunately, our understanding of cancer is still incomplete. Therefore, every day cancer researchers and clinicians work to manage and treat these horrible diseases.
It is tempting to view different topics as completely separate, but in fact the ideas we cover in this course are often connected to one another. If you don’t retain the vocabulary from module to module, those connections can be missed. As you continue on, remember to come back and review the terms you’ve learned in order to increase your depth of knowledge.