Chemotherapy
Overview
Chemotherapy is a type of cancer treatment that uses one or more anti-cancer drugs as part of a standardized chemotherapy regimen. It may aim to prolong life or to reduce symptoms (palliative chemotherapy). Chemotherapy is one of the major categories of the medical discipline specifically devoted to pharmacotherapy for cancer, which is called medical oncology.
History
The use of chemotherapy to treat cancer began in the 20th century, although it was not originally intended for that purpose. Originally used during World War I as chemical warfare, mustard gas was a deadly weapon that was later found to have suppressive effects on the bone marrow. Observing that bone marrow is one of the most rapidly dividing cells in the body, two pharmacologists from the Yale School of Medicine, Louis S. Goodman and Alfred Gilman, theorized that mustard gas could potentially be used to target other rapidly dividing cells, such as cancer cells.
Types of Chemotherapy
Chemotherapy drugs can be broadly classified into several categories based on their chemical structure and function. These include alkylating agents, antimetabolites, anthracyclines, plant alkaloids, topoisomerase inhibitors, and other antitumor agents.
Alkylating Agents
Alkylating agents are a type of chemotherapy drug that works by damaging the DNA of cells to prevent them from reproducing. These drugs are cell-cycle non-specific, meaning they can act on cells at any stage of the cell cycle.
Antimetabolites
Antimetabolites are a type of chemotherapy drug that mimics the normal substances within a cell. When these substances are incorporated into the cellular metabolism, they inhibit the use of normal metabolites needed for cellular division.
Anthracyclines
Anthracyclines are a class of drugs that are natural products of the bacterium Streptomyces. They work by intercalating DNA, disrupting the function of the enzymes topoisomerase IIα and IIβ.
Plant Alkaloids
Plant alkaloids are chemotherapy treatments derived from certain types of plants. The vinca alkaloids are derived from the periwinkle plant. They include vincristine and vinblastine, which block cell division by stopping mitosis (the process of cell division).
Topoisomerase Inhibitors
Topoisomerase inhibitors are drugs that interfere with the action of topoisomerase (enzymes that control the changes in DNA structure by catalyzing the breaking and rejoining of the phosphodiester backbone of DNA strands during the normal cell cycle).
Other Antitumor Agents
Other antitumor agents include monoclonal antibodies, immunomodulators, and drugs that inhibit angiogenesis or signal transduction pathways.
Administration
Chemotherapy can be given by a number of routes: intravenous, oral (in the form of a pill or a liquid), intramuscular (injected into a muscle), subcutaneous (under the skin), intrathecal (injected into the spinal canal), and more. The route of administration depends on the type and stage of the cancer being treated.
Side Effects
Chemotherapy drugs can cause side effects, as they target both cancer cells and healthy cells. Common side effects include fatigue, nausea, vomiting, decreased blood cell counts, hair loss, mouth sores, and skin changes. The severity of side effects depends on the type and dose of the drugs given, the length of treatment, and the individual patient's health status.
Future Directions
Future directions in chemotherapy include the development of new drugs, targeted therapy, personalized medicine, and nanotechnology-based delivery systems.