Chemotherapy - a method of treating malignant tumors with cytotoxic (toxic to cells, depressing vital functions of cells) of drugs. In oncology can be used two types of chemotherapy:
monochemotherapy (treatment one drug)
chemotherapy (treatment with several drugs simultaneously and / or sequentially).
Chemotherapy is most common. Chemotherapy can be used as a single treatment or in combination with other methods - surgery and radiotherapy. In the case of combined treatment of chemotherapy may be, as prior to other methods, and to complete treatment.
The mechanism of action in different chemoterapevtic drugs aimed at different stages (phases) of the life cycle and different processes in the cell. Virtually all chemotherapeutic drugs act on the "running" the cage and do not act on the inactive phase or resting phase cells, called G0. Consequently, the stability of the tumor to chemotherapy is primarily determined by the number of cells in phase G0. The more intense the cells grow and divide, they are more sensitive to chemotherapy. It should be emphasized that this is not important, it is a cancer cell or a completely normal - the effect will be approximately the same.
The most intensive chemotherapy is applied in the case of Leukemia (leukemia). Bone marrow cells are constantly dividing and mature. Consequently, the treatment of leukemia will also inhibit the normal operation (proliferation) of stem cells of bone marrow. A similar negative effect was observed with respect to the gonads and the gut epithelium. It is for this reason, the toxic effects of chemotherapy severely limits its portability.
Among the chemotherapeutic agents are the following groups:
Acting on all phases of the cell cycle.
Acting on certain phases of the cell cycle
Cytotoxic agents with different mechanisms of action
On the mechanisms of action are also several groups of drugs. Their classification has no rigid structure and is associated with features of the effects of the drug on the box:
Alkylating agents. The mechanism of action is explained by the formation of strong covalent bonds with the DNA chain. The precise molecular mechanisms of cell death after exposure to alkylating agents has not been established, but we know that they contribute to the error reading information and as a consequence, the suppression of the synthesis of proteins corresponding to a given code. There is a natural defense against alkylating agents in the form of glutathione ststemy, so high levels of glutathione in the tumor would indicate a poor efficacy of this group himoterapevticheskih drugs. Examples of drugs in this group are cyclophosphamide, embihin, nitrosourea drugs.
Antibiotics. Part of antibiotics have anti-tumor activity by acting on different phases of the cell cycle (G1, S, G2), but because they all have different mechanisms of action to the cell.
Antimetabolites. The mechanism of action is associated with blocking (competitive or noncompetitive) of natural metabolic (metabolic) processes in the cell. For example, methotrexate is similar in structure to folic acid, necessary for normal functioning of cells. Therefore, methotrexate will block its use, competitively inhibiting the operation of the service of the enzyme dihydrofolate reductase. The cell at the same dies due to excessive accumulation of the oxidized form of folate. Examples of other drugs: cytarabine, 5-flyuorouratsil.
Anthracyclines. Have in their composition anthracycline ring, which is able to interact with DNA. It is also believed that they were able to inhibit topoisomerase-II and form a large number of free radicals, which, in turn, can also damage the structure of DNA. Examples of drugs are rubomitsin, adriblastin.
Vinkalkaloidy. Named in honor of the plant Vinca rosea, from which they are received. The mechanism of action of their actions due to the possibility of binding of the protein tubulin that forms the cytoskeleton. Cytoskeleton of the cell and is required in the resting phase and mitosis. The absence of migration, cytoskeletal violates the right of the chromosomes in the fission process, which ultimately leads to cell death. Moreover, malignant cells are more sensitive to vinaklkloidam than healthy cells, as complex "vinca-tubulin" in the tumor tissue is more stable. Examples of drugs: vinblastine, vincristine, vindesine.
Platinum compounds. Platinum is a heavy metal, and therefore toxic to the body. On the mechanism of action similar to alkylating agents. Getting into the cell of platinum drugs can interact with DNA, disrupting its structure and function.
Epipodophyllotoxins. Synthetic analogues of substances from the extract of mandrake. Act on the nuclear enzyme topoisomerase-II and the DNA itself. Examples of drugs: etoposide, teniposide.
Other cytotoxic agents. Despite the different routes of exposure, the end point of application of these drugs is similar to. Some of them are similar to the action of alkylating agents (dacarbazine, procarbazine), part of the effect on topoisomerase (amsakrin), some could be related to antimetabolites (L-asparaginase, hydroxyurea). Not bad cytostatics and corticosteroids are sometimes used in the treatment of tumors.
Given that each group of chemotherapy drugs have their own characteristics, serious side effects, and complications of use, specialized treatment protocols are developed that help with minimal negative impact on the body to achieve maximum benefit from their use. Treatment protocols are improved in many leading clinics around the world, thus enhancing survival and quality of life of patients in compliance with all medical recommendations.
