Tumors are the result of mutations in cells: these chance mutations are errors in DNA replication that end up allowing a cell to "proliferate unchecked" (183). The human body is made of trillions of cells, many of which are constantly replaced through life. Since so many cells are regularly being replenished, an occasional mistake should be expected. However, we have many ways of preventing and treating cancer. Besides the use of the ABL-kinase in treating CML tumors, in what other ways do we humans alleviate cancer?
Think not only of technological methods. What does the body itself do that makes it so effective at preventing tumor cells from occurring and proliferating in the first place? (Refer to chapters 16 and 43 on DNA and the Immune System) Keep the theme of regulation in mind as you answer.
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From a medical point of view, two common ways of treating cancer are chemotherapy and radiation treatments. Both of these treatments weaken the body’s immune system, thus leaving the patients vulnerable to opportunistic diseases. As part of the third line of defense of the immune system, lymphocytes, among other things, are in charge of determining which cells are self and which cells are non-self. Bacteria, viruses, and tumor cells are considered non-self by the lymphocytes. Because of this, the body can determine whether a cell is cancerous. Once a lymphocyte recognizes a cancer cell as non-self, the lymphocyte induces a response that ultimately kills the cancer cell. The cancer cell is recognized as being non-self because of mutations in the DNA of the cancer cell. For one reason or another, the regulatory steps in the cell cycle are not met, leading to abnormal growth rates. Scientists hypothesize that many forms of cancer occur because of a change in the telomeres of the cancer cells. Telomeres normally limit the number of cycles a cell can perform, so when the telomeres are abnormally long and unregulated, the cell can undergo mitosis many times. Luckily for humans, lymphocyte cells can determine the cancerous cells and destroy them before the cancer cells can cause havoc to the body (most of the time).
ReplyDeleteNatural killer cells and other lymphocytes (as David stated) recognize a cancer cell by their antigen. Some cancerous cells are "careless" so to say and lose their antigen (through mutations). These cancerous cells are then considered non-self which are destroyed by natural killer cells and lymphocytes. (Campbell 903).
ReplyDeleteI recommend reading the last part of Chapter 19 titled "The Molecular Biology of Cancer" (p. 368-372). Mutations that alter certain genes that "normally regulate cell growth and division - the cell cycle -...can lead to cancer," (Campbell 369). Cancer-causing genes are known as oncogenes which induce tumors. There are genes known as "tumor-suppressor genes because the proteins they encode normally help prevent uncontrolled cell growth," (Campbell 369). There are many different proteins that arise from the tumor-suppressor genes. Some proteins repair damaged DNA to prevent the cell from accumulating cancer-causing mutations. Other proteins control the adhesion of cells to each other or to an ECM (extra-cellular matrix). "Proper cell anchorage is crucial in normal tissues - and often absent in cancers," (Campbell 369). Some proteins are components of cell-signaling pathways that inhibit the cell cycle. The theme of regulation is key when discussing cancer because without regulation in a cell, the cell has unrestricted growth and develops into a cancerous cell. Thus it is necessary to regulate the cell-cycle to prevent growth that could lead to dangerous circumstances.
Danyal excellently describes how the human body itself fights against cancer. Recently medical practices have developed which tap into the body’s potential to fight tumors using the same mechanisms Danyal outlined. Such therapies either “train” the immune system to recognize tumors or use antibodies and chemokines to activate an immune response against cancer cells. For example, monoclonal antibodies are used to prevent tumor growth by blocking cell receptors involved in growth. Monoclonal antibodies are also use to attack tumor cells and incite an immune response. Since, many tumors display antigens inappropriate to the cell type or development phase, antibodies are able to recognize these ‘self’ like tumors. Topical creams containing chemokines are also used to draw killer t cells to the tumor.
ReplyDeleteOther treatment procedures include use of anti-angiogenesis drugs and hormonal therapy. Anti-angiogenesis drugs impede extensive growth of blood vessels which tumors need to survive 1. Hormone therapy or oncology manipulates the endocrine system by using steroid inhibiting hormones. Since steroids are necessary for gene expression for certain kinds of tumors, steroid inhibitors can cure some cancers. Hormone inhibitors also target hormone sensitive parts of the body. For example, tamoxifen which inhibits estrogen are used to treat breast cancer.
First of all, thanks for the input!
ReplyDeleteTo begin, I'll first say that while most cancers originate from a tumor, many tumors are benign and don't harm the body. Malignant tumors, however, grow uncontrollably and metastisize (spread to other parts of the body). The body tries to prevent both benign and malignant tumors from occuring, but artificial treatments generally are only used on malignant tumors.
David mentioned chemotherapy and radiation therapy, which undiscriminately kill cells. These treatments are very risky, since radiation therapy and chemotherapy can disrupt healthy cells' abilities to replicate. This creates a host of problems with cells that are constantly replenished, such as erythrocytes and intestinal lining. It's worth noting that tumors can sometimes be removed with simple surgery prior to metastasis.
All of you talked about what we recently learned: natural killer cells can identify self from not-self, and are usually able to "see" and kill cancerous cells. However, you didn't say anything about our cells' basic ability of "mismatch repair" (299, Campbell). Nuclease enzymes can cut out damaged DNA (which may cause cancerous growth), which is replaced by a DNA polymerase. This is but one example of mismatch repair, but you can see that this basic function is probably the first step in preventing tumors.
Cancers sap the body of nutrients (carbs, proteins, vitamins, minerals, water, etc.) to do unnecessary growth and replication. This obviously hurts the rest of the body. Internal regulation of the body by mismatch repair and NK cells maintains homeostasis since cancers are not "normal" to a healthy body and disrupt the body's internal balance.