An antimetabolite is a chemical that inhibits the use of a metabolite

Metabolite

Metabolites are the intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. A primary metabolite is directly involved in normal growth, development, and reproduction. Alcohol is an example of a primary metabolite produced in large-scale by industrial...

, which is another chemical that is part of normal metabolism

Metabolism

Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

. Such substances are often similar in structure to the metabolite that they interfere with, such as the antifolate

Antifolate

Antifolates are drugs that impair the function of folic acids. Many are used in cancer chemotherapy, some are used as antibiotics or antiprotozoal agents....

s that interfere with the use of folic acid

Folic acid

Folic acid and folate , as well as pteroyl-L-glutamic acid, pteroyl-L-glutamate, and pteroylmonoglutamic acid are forms of the water-soluble vitamin B9...

. The presence of antimetabolites can have toxic effects on cells, such as halting cell growth

Cell growth

The term cell growth is used in the contexts of cell development and cell division . When used in the context of cell division, it refers to growth of cell populations, where one cell grows and divides to produce two "daughter cells"...

 and cell division

Cell division

Cell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...

, so these compounds are used as chemotherapy

Chemotherapy

Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....

 for cancer.

Cancer treatment

Antimetabolites can be used in cancer

Cancer

Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

 treatment, as they interfere with DNA production and therefore cell division and the growth of tumors. Because cancer cells spend more time dividing than other cells, inhibiting cell division harms tumor cells more than other cells.

Anti-metabolites masquerade as a purine

Purine

A purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines, including substituted purines and their tautomers, are the most widely distributed kind of nitrogen-containing heterocycle in nature....

 (azathioprine

Azathioprine

Azathioprine is a purine analogue immunosuppressive drug. It is used to prevent organ rejection following organ transplantation and to treat a vast array of autoimmune diseases, including rheumatoid arthritis, pemphigus, inflammatory bowel disease , multiple sclerosis, autoimmune hepatitis, atopic...

, mercaptopurine

Mercaptopurine

Mercaptopurine is an immunosuppressive drug.It is a thiopurine.-Uses:...

) or a pyrimidine

Pyrimidine

Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring...

, chemicals that become the building-blocks of DNA. They prevent these substances becoming incorporated in to DNA during the S phase

S phase

S-phase is the part of the cell cycle in which DNA is replicated, occurring between G1 phase and G2 phase. Precise and accurate DNA replication is necessary to prevent genetic abnormalities which often lead to cell death or disease. Due to the importance, the regulatory pathways that govern this...

 (of the cell cycle

Cell cycle

The cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...

), stopping normal development and division.

They also affect RNA synthesis. However, because thymidine

Thymidine

Thymidine is a chemical compound, more precisely a pyrimidine deoxynucleoside. Deoxythymidine is the DNA nucleoside T, which pairs with deoxyadenosine in double-stranded DNA...

 is used in DNA but not in RNA (where uracil

Uracil

Uracil is one of the four nucleobases in the nucleic acid of RNA that are represented by the letters A, G, C and U. The others are adenine, cytosine, and guanine. In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced by thymine.Uracil is a common and...

 is used instead), inhibition of thymidine synthesis via thymidylate synthase

Thymidylate synthase

Thymidylate synthetase is the enzyme used to generate thymidine monophosphate , which is subsequently phosphorylated to thymidine triphosphate for use in DNA synthesis and repair....

 selectively inhibits DNA synthesis over RNA synthesis.

Due to their efficiency, these drugs are the most widely used cytostatics.

In the ATC system

Anatomical Therapeutic Chemical Classification System

The Anatomical Therapeutic Chemical Classification System is used for the classification of drugs. It is controlled by the WHO Collaborating Centre for Drug Statistics Methodology , and was first published in 1976....

, they are classified under L01B.

Antibiotics

Antimetabolites may also be antibiotics, such as sulfanilamide drugs, which inhibit dihydrofolate synthesis in bacteria by competing with para-aminobenzoic acid.

Types

Main representatives of these drugs are:

• purine analogue
  Purine analogue
  Purine analogues are antimetabolites which mimic the structure of metabolic purines.* 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...
  
  s
• pyrimidine analogue
  Pyrimidine analogue
  Pyrimidine analogues are antimetabolites which mimic the structure of metabolic pyrimidines.-Examples:Examples include:* 5-fluorouracil which inhibits thymidylate synthase.* Floxuridine * Cytosine arabinoside...
  
  s
• antifolate
  Antifolate
  Antifolates are drugs that impair the function of folic acids. Many are used in cancer chemotherapy, some are used as antibiotics or antiprotozoal agents....
  
  s

External links

• Overview at University of Nebraska