chemotherapy

the use of chemical agents to treat or control disease (or mental illness)

Chemotherapy is the use of chemical substances to treat disease. In its modern-day use, it refers almost exclusively to cytostatic drugs used to treat cancer.In its non-oncological use, the term may also refer to antibiotics (''antibacterial chemotherapy''). In that sense, the first modern chemotherapeutic agent was Paul Ehrlich's arsphenamine, an arsenic compound discovered in 1909 and used to treat syphilis. This was later followed by sulfonamides discovered by Gerhard DomagkDomagk and penicillin G discovered by Alexander Fleming.Other uses of cytostatic chemotherapy agents (including the ones mentioned below) are the treatment of autoimmune diseases and the suppression of transplant rejections (see immunosuppression and DMARDs).

History - mainhistory of cancer chemotherapy The era of chemotherapy began in the 1940s with the first uses of nitrogen mustards and folic acid inhibitors. Cancer drug development since then has exploded into a multi-billion dollar industry. The targeted-therapy revolution has arrived, but the principles and limitations of chemotherapy discovered by the early researchers still apply.

Principles - Cancer is the uncontrolled growth of cell (biology)cells due to damage to DNA (mutations) and, occasionally, due to an genetic disorderinherited propensity to develop certain tumortumours. Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body - in other words, the body attacks its own cells. In a contrast, transplant rejection happens because a normal healthy human immune system can distinguish foreign tissues and attempts to destroy them. Also the reverse situation, called graft-versus-host disease, may take place.Broadly, most ''chemotherapeutic'' drugs work by impairing mitosis (cell division), effectively targeting fast-dividing cells. As these drugs cause damage to cells they are termed ''cytotoxic''. Some drugs cause cells to undergo apoptosis (so-called "cell suicide").Unfortunately, scientists have yet to be able to locate specific features of malignant and immune cells that would make them uniquely targetable (barring some recent examples, such as the Philadelphia chromosome as targeted by imatinib). This means that other fast dividing cells such as those responsible for hair growth and for replacement of the intestineintestinal epithelium (lining) are also affected. However, some drugs have a better side-effect profile than others, enabling physiciandoctors to adjust treatment regimens to the advantage of patients in certain situations.As chemotherapy affects cell division, tumours with high ''growth fractions'' (such as acute myelogenous leukemia and the lymphomas, including Hodgkin's disease) are more sensitive to chemotherapy, as a larger proportion of the targeted cells are undergoing cell division at any time.Chemotherapeutic drugs affect "younger" tumours (i.e. less differentiated) more effectively, because at a higher grade of differentiation, the propensity to growth usually decreases. Near the center of some solid tumours, cell division has effectively ceased, making them insensitive to chemotherapy. Another problem with solid tumours is the fact that the chemotherapeutic agent often does not reach the core of the tumour. Solutions to this problem include radiation therapy (both sealed source radiotherapybrachytherapy and external beam radiotherapyteletherapy) and surgery.

Types and dosage - The majority of chemotherapeutic drugs can be divided in to: alkylating agents, antimetabolites, plant alkaloids, topoisomerase inhibitors, and antitumour agents. All of these drugs affect cell division or DNA synthesis and function in some way.Some newer agents don't directly interfere with DNA. These include the new tyrosine kinase inhibitor ''imatinibimatinib mesylate'' (Gleevec® or Glivec®), which directly targets a molecular abnormality in certain types of cancer (chronic myelogenous leukemia, gastrointestinal stromal tumors).In addition, some drugs may be used which modulate tumour cell behaviour without directly attacking those cells. Hormone treatments fall into this category of adjuvant therapies.''Dosage'' of chemotherapy can be difficult: if the dose is too low, it will be ineffective against the tumor, while at excessive doses the toxicity (side-effects, neutropenia) will be intolerable to the patient. This has led to the formation of detailed "dosing schemes" in most hospitals, which give guidance on the correct dose and adjustment in case of toxicity. In immunotherapy, they are in principle used in smaller dosages than in the treatment of malign diseases.In most cases, the dose is adjusted for the patient's ''body surface area'', a composite measure of weight and height that mathematically approximates the body volume. The BSA is usually calculated with a mathematical formula or a nomogram, rather than by direct measurement.

Alkylating agents - Alkylating agents are so named because of their ability to add alkyl groups to many electronegative groups under conditions present in cells. They stop tumour growth by cross-linking guanine nucleobases in DNA double-helix strands - directly attacking DNA. This makes the strands unable to uncoil and separate. As this is necessary in DNA replication, the cells can no longer divide. These drugs acts mainly nonspecifically, some of them requires conversion into active substances ''in vivo'' (e.g. !cyclophosphamide).Cyclophospha mide? is one of the most potent immunosuppressive substances. In small dosages, it is very efficient in the therapy of systemic lupus erythematosus, autoimmune hemolysis#hemolytic anemiahemolytic anemias, Wegener's granulomatosis and other autoimmune diseases. High dosages cause pancytopenia and hemorrhagic cystitis. Other selected examples: cisplatin, carboplatin, ifosfamide, chlorambucil, busulfan, thiotepa, nitrosoureas and others.

Anti-metabolites - Anti-metabolites masquerade as purine ((azathioprine, mercaptopurine)) or pyrimidine - which become the building blocks of DNA. They prevent these substances becoming incorporated in to DNA during the "S" phase (of the cell cycle), stopping normal development and division. They also affect RNA synthesis. Due to their efficiency, these drugs are the most widely used cytostatics. An important example is Fluorouracil5-fluorouracil (5FU), which inhibits thymidylate synthase. Fludarabine inhibits function of multiple DNA polymerases, DNA primase, DNA ligase I and is S phase-specific (since these enzymes are highly active during DNA replication).Methotrexate, a folic acid analogue, prevents the formation of tetrahydrofolate, essential for purine and pyrimidine synthesis, by inhibiting dihydrofolate reductase. This leads to inhibited production of DNA, RNA and proteins (as tetrahydrofolate is also involved in the synthesis of amino acids serine and methionine).Azathioprine is the main immunosuppressive cytotoxic substance. It is widely used in transplantations to control rejection reactions. It is nonenzymatically cleaved to 6-mercaptopurine that acts as a purine analogue and an inhibitor of DNA synthesis. By preventing the clonal expansion of lymphocytes in the induction phase of the immune response, it affects both the cell immunitycell and the humoral immunity. It also successfully suppresses autoimmunity.

Plant alkaloids - These alkaloids are derived from plants and block cell division by preventing microtubule function. Microtubules are vital for cell division and without them it can not occur. The main examples are vinca alkaloids and taxanes.

Vinca alkaloids - Vinca alkaloids bind to specific sites on tubulin, inhibiting the assembly of tubulin into microtubules (M phase of the cell cycle). They are derived from the Madagascar periwinkle, ''Catharanthus roseus'' (formerly known as ''Vinca rosea''). The vinca alkaloids include: -

Vincristine

Vinblastine

Vinorelbine

Vindesine

Podophyllotoxin - Podophyllotoxin is a plant-derived compound used to produce two other cytostatic drugs, etoposide and teniposide. They prevent the cell from entering the G1 phase (the start of DNA replication) and the replication of DNA (the S phase). The exact mechanism of its action still has to be elucidated.The substance has been primarily obtained from the American mayapple (''Podophyllum peltatum''). Recently it has been discovered that a rare Himalayan Mayapple (''Podophyllum hexandrum'') contains it in a much greater quantity, but as the plant is endangered, its supply is limited. Studies have been conducted to isolate the genes involved in the substance's production, so that it could be obtained genetic engineeringrecombinantively.

Taxanes - Taxanes are derived from the TaxusPacific yew tree, ''Taxus brevifolia''. Taxanes enhance stability of microtubules, preventing the separation of chromosomes during anaphase. Taxanes include: -

Paclitaxel

Docetaxel

Topoisomerase inhibitors - Topoisomerases are essential enzymes that maintain the topology of DNA. Inhibition of type I or type II topoisomerases interferes with both Transcription (genetics)transcription and DNA replicationreplication of DNA by upsetting proper DNA supercoiling. Some type I topoisomerase inhibitors include ''camptothecins'': irinotecan and topotecan. Examples of type II inhibitors include amsacrine, etoposide, etoposide phosphate, and teniposide. The latter are semisynthetic derivatives of epipodophyllotoxins, alkaloids naturally occurring in the root of mayapple (''Podophyllum peltatum'') .

Antitumour antibiotics - There are many differing antitumour antibiotics, but generally they prevent cell division by several ways: (1) binding to DNA through intercalation between two adjacent nucleotide bases and making it unable to separate, (2) inhibiting ribonucleic acid (RNA), preventing enzyme synthesis, (3) interfering with cell replication. They are products of various strains of the soil fungus ''Streptomyces''. Examples are ''anthracyclines'' (doxorubicin, daunorubicin and epirubicin, which also inhibit topoisomerase II), actinomycin, bleomycin, mitomycin and plicamycin. Bleomycin acts in unique way through oxidation of a DNA-bleomycin-Fe(II) complex and forming free radicals, which induce damage and chromosomal aberrations. The most important immunosuppressant from this group is dactinomycin, which is used to in kidney transplantations.

Hormonal therapy - Several malignancies responds to hormonal therapy. Strictly speaking, this is not chemotherapy. Cancer arising from certain tissues, including the mammary and prostate glands, may be inhibited or stimulated by appropriate changes in hormone balance.

Steroids (often dexamethasone) can inhibit tumour growth or the associated edema (tissue swelling), and may cause regression of lymph node malignancies.

Prostate cancer is often sensitive to finasteride, an agent that blocks the peripheral conversion of testosterone to dihydrotestosterone.

Breast cancer cells often highly express the estrogen and/or progesterone receptor. Inhibiting the production (with aromatase inhibitors) or action (with tamoxifen) of these hormones can often be used as an adjunct to therapy.

Gonadotropin-releasing hormone agonists (GnRH), such as goserelin possess a paradoxic negative feedback effect followed by inhibition of the release of FSH (follicle-stimulating hormone) and LH (luteinizing hormone), when given continuously.Some other tumours are also hormone dependent, although the specific mechanism is still unclear.

Delivery - Most chemotherapy is Route of administrationdelivered intravenously, although there are a number of agents that can be administered orally (e.g. melphalan and gemcitabine). Depending on the patient, the cancer, the stage of cancer, the type of chemotherapy, and the dosage, IV chemotherapy may be given on either an inpatient or outpatient basis. For continuous, frequent or prolonged IV chemotherapy administration, various systems may be surgically inserted into the vasculature to maintain access. Commonly used systems are the Hickman line, the Port-a-Cath or the PICC line. These have a lower infection risk, are much less prone to phlebitis or extravasation, and abolish the need for repeated insertion of peripheral cannulae.

Treatment schemes - There are a number of strategies in the administration of chemotheraputic drugs used today. Chemotherapy may be given with a curative intent or it may aim to prolong life or to palliate symptoms.''Combined modality chemotherapy'' is the use of drugs with other Cancer#Treatmentscancer treatments, such as radiation therapy or surgery. Most cancers are now treated in this way. ''Combination chemotherapy'' is a similar practice which involves treating a patient with a number of different drugs simultaneously. The drugs differ in their mechanism and side effects. The biggest advantage is minimising the chances of resistance developing to any one agent.In ''neoadjuvant chemotherapy'' (''pre''operative treatment) initial chemotherapy is aimed for shrinking the primary tumour, thereby rendering local therapy (surgery or radiotherapy) less destructive or more effective.''Adjuvant chemotherapy'' (''post''operative treatment) can be used when there is little evidence of cancer present, but there is risk of recurrence. This can help reduce chances of resistance developing if the tumour does develop. It is also useful in killing any cancerous cells which have spread to other parts of the body. This is often effective as the newly growing tumours are fast-dividing, and therefore very susceptible.''Palliative chemotherapy'' is given without curative intent, but simply to decrease tumor load and increase life expectancy. For these regimens, a better toxicity profile is generally expected.Most chemotherapy regimens require that the patient is capable to undergo the treatment. Performance status is often used as a measure to determine whether a patient can receive chemotherapy, or whether dose reduction is required.

Side-effects - The treatment can be physically exhausting for the patient. Current chemotheraputic techniques have a range of side effects mainly affecting the fast-dividing cells of the body. Important common side-effects include (dependent on the agent):

alopeciahair loss

nausea and vomiting

diarrhea or constipation

anemia

depression of the immune system hence (potentially lethal) infections and sepsis

hemorrhage

secondary neoplasms

cardiotoxicity

hepatotoxicity

nephrotoxicity

ototoxicityVirtually all chemotherapeutic regimens can cause depression of the immune system, often by paralysing the bone marrow and leading to a decrease of white blood cells, red blood cells and platelets. The latter two, when they occur, are improved with blood transfusion. Neutropenia (a decrease of the neutrophil granulocyte count below 0.5 x !10⁹/lit re)? can be improved with synthetic G-CSF (granulocyte-colony stimulating factor, e.g. filgrastim, lenograstim, Neupogen®, Neulasta®.)In very severe ''myelosuppression'', which occurs in some regimens, almost all the bone marrow stem cells (cells which produce white blood cellswhite and red blood cells) are destroyed, meaning ''allogenic'' or ''autologous'' bone marrow transplantbone marrow cell transplants are necessary. (In autologous BMTs, cells are removed from the patient before the treatment, multiplied and then re-injected afterwards; in ''allogenic'' BMTs the source is a donor.) However, some patients still develop diseases because of this interference with bone marrow.Nausea and vomiting caused by chemotherapy; stomach upset may trigger a strong urge to vomit, or forcefully eliminate what is in the stomach.Stimulation of the vomiting center results in the coordination of responses from the diaphragm, salivary glands, cranial nerves, and gastrointestinal muscles to produce the interruption of respiration and forced expulsion of stomach contents known as retching and vomiting. The vomiting center is stimulated directly by afferent input from the vagal and splanchnic nerves, the pharynx, the cerebral cortex, cholinergic and histamine stimulation from the vestibular system, and efferent input from the chemoreceptor trigger zone (CTZ). The CTZ is in the area postrema, outside the blood-brain barrier, and is thus susceptible to stimulation by substances present in the blood or cerebral spinal fluid. The neurotransmitters dopamine and serotonin stimulate the vomiting center indirectly via stimulation of the CTZ.The 5-HT3 inhibitors are the most effective antiemetics and constitute the single greatest advance in the management of nausea and vomiting in patients with cancer. These drugs are designed to block one or more of the signals that cause nausea and vomiting. The most sensitive signal during the first 24 hours after chemotherapy appears to be 5-HT3. Blocking the 5-HT3 signal is one approach to preventing acute emesis (vomiting), or emesis that is severe, but relatively short-lived. Approved 5-HT3 inhibitors include: dolasetron (Anzemet®), granisetron (Kytril®), and ondansetron (Zofran®). The newest 5-HT3 inhibitor, Aloxi® (palonosetron), has a distinct advantage over the other 5-HT3 inhibitors because, in addition to preventing acute nausea and vomiting, Aloxi® also prevents delayed nausea and vomiting, which occurs during the 2-5 days after treatment. Aloxi® is the only drug in its class that is approved by the FDA for the treatment of delayed nausea and vomiting.Some studiesrefmarijuana and patient groups claim that the use of cannabinoids derived from marijuana during chemotherapy greatly reduces the associated nausea and vomiting, and enables the patient to eat. Some synthetic derivatives of the active substance in marijuana (tetrahydrocannabinol or THC) are in development for this indication.In particularly large tumors, such as large lymphomas, some patients develop tumor lysis syndrome from the rapid breakdown of malignant cells. Although prophylaxis is available and is often initiated in patients with large tumors, this is a dangerous side-effect which can lead to death if left untreated.Chemotherapy may increase the risk of cardiovascular disease and occasionally leads to secondary cancer.Some patients report Attention Deficit Disorderattention deficit especially when attempting tasks like driving a car that require continued concentration. The informal term "Chemo Headchemo head" is often used to describe the feeling. This may be a secondary symptom due to the effects of anemia.

See also -

Cancer

Gene therapy

Experimental cancer treatments

Chemotherapy regimens

References -

notemarijuana Tramer MR, Carroll D, Campbell FA, Reynolds DJ, Moore RA, McQuay HJ. ''Cannabinoids for control of chemotherapy induced nausea and vomiting: quantitative systematic review.'' British Medical JournalBMJ 2001;323:16-21. PMID 11440936.

External links -

thedoctorslounge.net - Chemotherapy Regimens Database

chemocare.com - Chemocare.com chemotherapy drug informationChemotherapeutic agents Category:Cancer !treatmentsCategory:Chemotherap eutic? agents !Category:Oncologyde:Chemothera piees:Quimioterapiafr:Chimioth érapieid:Chemotherapylt:Chemo terapijanl:Chemotherapieja:化 学療法pl:Chemioterapiapt:Qu imioterapiaru:Химиотер апияfi:Kemoterapia?

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