By: Annie Hu
Cancer is a huge health issue that affects many people, due to how common it is. Cancer is caused by rapid growth of mutated cells, and this growth and the mutations in the cells allows cancer to spread uncontrollably throughout the body. Normal cells behave simply by reproducing when it is necessary to replace old cells that die. But if this process is disrupted, the consequences can be dire. A burst of abnormal cell growth can form tissue called tumors, and if these tumors are cancerous, they can spread to other body parts through a process known as metastasis. How can cancer be stopped? If we go back to the origin of how cancer forms, the answer lies in how to halt the rapid growth of cells and treat cancer.
Photo by National Cancer Institute on Unsplash
Several different treatments exist for cancer, including chemotherapy, radiation therapy, surgery, and immunotherapy; though today we will focus on chemotherapy.
Chemotherapy involves using drugs to target cancer cells and stop them from growing and spreading. Chemotherapy works by changing the cell cycle of abnormally multiplying cells.
To better understand how chemotherapy targets cancer, let's look at the cell cycle. The cell cycle is the series of phases through which a cell fully matures, reproduces more cells, then dies. As a quick summary of how the cell cycle works, the cell lives most of its life in what is called the interphase where it carries out cell functions and eventually prepares to divide. When it needs to reproduce, the cell goes into mitosis (where the cell divides). The daughter cells of this reproduction then start over by entering their own interphases to prepare for another division.
The interphase itself consists of several stages. The G1 Phase is where the cell grows and prepares for division. Then the cell enters the S Phase where new DNA is synthesized and replicated to be given to the new cell in division. After the S Phase the cell enters a G2 Phase where the new genetic material is condensed to prepare for division of two separate cells in the M phase (mitosis).
Image Credit: Annie Hu
The drugs used in chemotherapy are grouped by their chemical structure, how they work in the cell cycle, and how they work with other drugs. For example, alkylating agents are a type of chemotherapy which targets the DNA of the cancer cells and damages the DNA. This stops the cell from reproducing and in doing so, influences all stages of the cell cycle of the cancer cell. But this treatment is risky because the drugs can also damage healthy cells and can influence bone marrow cells by inhibiting the creation of healthy new blood cells. Another type of drug is nitrosoureas, which are alkylating agents, but also have the ability to travel to the brain and treat tumors there.
Antimetabolites are a class of chemotherapy drug that works by taking the place of normal RNA and DNA components to disrupt DNA replication. This replacement makes it impossible for the DNA to make copies in the S Phase, thus stopping the cell from reproducing. Another interesting classification for chemotherapeutic drugs are mitotic inhibitors, which stop the cell from dividing. Mitotic inhibitor compounds come from natural products and plants and are also referred to as plant alkaloids. Though these compounds are given in limited doses because mitotic inhibitors can cause nerve damage. The sheer variety of chemotherapy drugs show that each different type of drug comes with different risks and benefits to specific types of cancer, depending on the manner and reach with which it can inhibit the cell cycle of more types of cells.
Chemo targets cancer cells because they divide and form new cells much more quickly than healthy cells. However, it is important to note that some healthy fast dividing cells like those found in your hair, nails, and bone marrow, might also be killed by chemotherapeutic drugs. As well as this, chemotherapy is often taken orally or through a vein, which means that the chemicals are not concentrated to just one area of the body like they would be in other types of cancer treatments (like radiation therapy). The effects of chemo might cause harm through other healthy cells all throughout the body this way. Depending on previous health conditions, patients also may experience other side effects such as vomiting, infection, and pain in the limbs. Therefore, chemo drugs should be treated with care and a balance must be considered. That way, harmful side effects can be avoided when possible. Fortunately, many non-cancerous cells that may have been affected by chemo drugs have been shown to heal with time after the medicine has been administered, so oftentimes chemotherapy is still a great option to kill cancerous cells.
Hopefully you were able to learn something new about the nature of cancer and how therapies work to stop it at its roots. Progress towards improving the efficacy of chemotherapeutics and trying to decrease harmful side effects is a very active field of study, so there will be lots to see in the upcoming years as chemotherapy continues to be developed. Thank you for reading!
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Photo by National Cancer Institute on Unsplash
Image Credit: Annie Hu
What Did You Learn?
Questions:
What do chemotherapeutic drugs target to attempt to stop/hinder the spread of cancer?
Chemotherapeutic drugs aim to stop the spread of cancer through targeting phases of the cell cycle and preventing cancer cells from replicating. For example, alkylating agents are a type of drug which damages the DNA of malignant cancer cells, and this effectively damages activity occurring in all four main phases of the cell cycle (G1, S, G2, M). Other drugs like antimetabolites are able to inhibit synthesis of new DNA in the S Phase and stop the cell cycle that way. The main theme of chemotherapy drugs, however, is their ability to halt the cell cycle to stop cancer.
What are a few risks associated with using chemotherapy?
Chemotherapy targets fast growing cells, which means that the drugs could also kill off healthy cells like those in the hair, nails, and bones. The chemicals are also spread throughout the body rather than concentrated in one region because of the manner in which the drugs are administered, which is either orally or intravenously. This increases a risk of side effects associated with the killing of good cells in other regions of the body, like inhibiting the creation of blood from marrow cells, and also maybe causing nerve damage to brain tissue.