Aminopterin
Encyclopedia
Aminopterin a 4-amino analog
of folic acid
, is an antineoplastic drug with immunosuppressive properties used in chemotherapy
. Aminopterin is a synthetic derivative of pterin
. Aminopterin works as an enzyme inhibitor
by competing for the folate binding site of the enzyme
dihydrofolate reductase
. Its binding affinity for dihydrofolate reductase effectively blocks tetrahydrofolate synthesis. This results in the depletion of nucleotide
precursors and inhibition of DNA
, RNA
, and protein synthesis
.
, the antifolate
activity of aminopterin was first used by Sidney Farber
in 1947 to induce remissions among children with leukemia
. Aminopterin was later marketed by Lederle Laboratories (Pearl River, New York) in the United States from 1953 to 1964 for the indication of pediatric leukemia. The closely related antifolate methotrexate
was simultaneously marketed by the company during the same period. Aminopterin was discontinued by Lederle Laboratories in favor of methotrexate due to manufacturing difficulties of the former.
During the period Aminopterin was marketed, the agent was used off-label to safely treat over 4,000 patients with psoriasis in the United States, producing dramatic clearing of lesions.
The use of aminopterin in cancer treatment was supplanted in the 1950s by methotrexate
due to the latter's better therapeutic index
in a rodent tumor model. Now in a more pure preparation and supported by laboratory evidence of superior tumor cell uptake in vitro, aminopterin is being investigated in clinical trials in leukemia as a potentially superior antifolate to methotrexate.
The compound was explored as an abortifacient
in the 1960s and earlier, but was associated with congenital malformations. Similar congenital abnormalities have been documented with methotrexate, and collectively their teratogenic effects have become known as the fetal aminopterin syndrome. When a similar cluster of abnormalies appears in the absence of exposure to antifolates it is referred to as aminopterin-like syndrome without aminopterin.
Although the use of aminopterin as a rodenticide is widely asserted on the web and elsewhere, there is no evidence that it has ever been used for that purpose either in the United States or elsewhere in the world. The preparation of the molecule is complex and expensive. It is also unstable in the environment due to degradation by light and heat. The apparently mistaken association of aminopterin with its use as a rodenticide likely dates back to a 1951 patent issued to the American Cyanamid Company (then the holding company of Lederle Laboratories) that is commonly cited by a variety of reference textbooks. Aminopterin has a single-dose LDLo
of 2.5 mg/kg when orally administered to rats.
Aminopterin and methotrexate
are widely used in selection media (such as HAT medium
) for cell culture
.
reported
that aminopterin was the chemical linked to the 2007 Menu Foods
pet food contamination incident
. The incident resulted in a massive recall of the affected foods. The link to aminopterin was confirmed by New York State Agriculture Commissioner Patrick Hooker and Dr. Donald Smith, Dean of Cornell University
's College of Veterinary Medicine, in a statement released on the same day.
On March 27, the ASPCA Animal Poison Control Center expressed concern that the problem may not yet be fully understood and that other contaminants may be involved, noting that "clinical signs reported in cats affected by the contaminated foods are not fully consistent with the ingestion of rat poison containing aminopterin".
On March 30 it was widely reported that the United States Food and Drug Administration had found melamine
in wheat gluten that was used in the pet foods in question. These same reports stated that the FDA had failed to find evidence of aminopterin in the wheat gluten. Tests at the University of Guelph
in Ontario
, Canada detected aminopterin in some pet food samples, but only in concentrations of parts per billion or parts per trillion, amounts too low to cause the symptoms seen.
Supralethal doses of aminopterin may be rescued with the antidote Leucovorin (also known as folinic acid), a reduced
form of folic acid
which bypasses dihydrofolate reductase, the enzyme inhibited by aminopterin. Leucovorin has been used in rats, dogs and humans to rescue aminopterin toxicity. Leucovorin rescue is a therapeutic maneuver intentionally employed with antifolates to achieve tumoricidal drug concentrations that would otherwise be lethal to the patient.
In humans, leucovorin rescue at overdosages lower than 10 mg aminopterin in an average 70 kg adult should comprise an initial leucovorin dose of at least 20 mg (10.0 mg/m2), given intravenously (preferably), or orally. Subsequent doses of 20 mg (which may be taken orally) should be given at 6 hour intervals until hematological abnormalities are improved.
Massive aminopterin overdosage in humans (i.e. > 40 mg AMT in an average 70 kg adult), should be approached with an initial leucovorin dose of 100 mg (50 mg/m2), given intravenously and continued at 6 hour intervals until the hematological abnormalities are improved (likely 8–12 courses or more). Additionally, to prevent reversible aminopterin-mediated nephrotoxicity manifesting as increases in serum creatinine and which further delays drug elimination, urinary alkalinization with and volume expansion should be considered in cases of massive aminopterin overdosage, particularly those involving greater than 100 mg AMT in an average 70 kg adult human.
Consistent with the known enterohepatic cycling of the related antifolate methotrexate, oral activated charcoal, and saline cathartic
or sorbitol
may promote excretion if an overdose of aminopterin is suspected. However, rescue with leucovorin should form the backbone of treatment.
The vitamin folic acid is an oxidized precursor to reduced folates that is upstream of the blockade at dihydrofolate reductase, and compared to leucovrin is recognized as a very weak antidote to the toxic effects of antifolates that is inappropriate for use in cases of acute intoxication. Minnich et al. dosed mongrel dogs subcutaneously with aminopterin and folic acid simultaneously to test whether folic acid can rescue animals from the lethality and toxicity of aminopterin Dogs were given 0.020, 0.046, 0.044 escalated to 0.088, and 0.097 mg/kg aminopterin each day for 7 to 12 days. Folic acid was given in a weight ratio to aminopterin of 200:1 to 800:1. All animals survived. In contrast, animals given aminopterin in an amount of 0.041 mg/kg/day x 6 days without folic acid died. Thus, when the ratio of folic acid to aminopterin was 200:1 and greater, all of the subjects survived on regimens that would have otherwise been uniformly fatal to all subjects.
Similar effects have been noted in rodent species as well, where the range for rescue by folic acid was fairly narrow and highly dependent on the timing (optimal of 1 hour prior to aminopterin) of administration in relation to aminopterin. The temporal relationship between folic acid administration and rescue has been interpreted as the necessary period of time required for the vitamin to be converted in vivo to reduced forms.
Analog (chemistry)
In chemistry, a structural analog , also known as chemical analog or simply analog, is a compound having a structure similar to that of another one, but differing from it in respect of a certain component. It can differ in one or more atoms, functional groups, or substructures, which are replaced...
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...
, is an antineoplastic drug with immunosuppressive properties used in chemotherapy
Chemotherapy
Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
. Aminopterin is a synthetic derivative of pterin
Pterin
Pterin is a heterocyclic compound composed of a pteridine ring system, with a keto group and an amino group on positions 4 and 2 respectively...
. Aminopterin works as an enzyme inhibitor
Enzyme inhibitor
An enzyme inhibitor is a molecule that binds to enzymes and decreases their activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors. They are also used as herbicides and pesticides...
by competing for the folate binding site of the enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
dihydrofolate reductase
Dihydrofolate reductase
- Function :Dihydrofolate reductase converts dihydrofolate into tetrahydrofolate, a methyl group shuttle required for the de novo synthesis of purines, thymidylic acid, and certain amino acids...
. Its binding affinity for dihydrofolate reductase effectively blocks tetrahydrofolate synthesis. This results in the depletion of nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
precursors and inhibition of DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
, RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
, and protein synthesis
Protein biosynthesis
Protein biosynthesis is the process in which cells build or manufacture proteins. The term is sometimes used to refer only to protein translation but more often it refers to a multi-step process, beginning with amino acid synthesis and transcription of nuclear DNA into messenger RNA, which is then...
.
Uses
Discovered by Dr. Yellapragada SubbaraoYellapragada Subbarao
Yellapragada Subbarao was an Indian biochemist who discovered the function of Adenosine Triphosphate as a energy source in the cell, and made important contributions to the treatment of cancer. Most of his career was spent in the United States...
, 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....
activity of aminopterin was first used by Sidney Farber
Sidney Farber
Sidney Farber was a pediatric pathologist. He was born in 1903 in Buffalo, New York, the third oldest of a family of 14 children. He was a graduate of the University of Buffalo in 1923. He took his first year of medical school at the Universities of Heidelberg and Freiburg in Germany. He entered...
in 1947 to induce remissions among children with leukemia
Leukemia
Leukemia or leukaemia is a type of cancer of the blood or bone marrow characterized by an abnormal increase of immature white blood cells called "blasts". Leukemia is a broad term covering a spectrum of diseases...
. Aminopterin was later marketed by Lederle Laboratories (Pearl River, New York) in the United States from 1953 to 1964 for the indication of pediatric leukemia. The closely related antifolate methotrexate
Methotrexate
Methotrexate , abbreviated MTX and formerly known as amethopterin, is an antimetabolite and antifolate drug. It is used in treatment of cancer, autoimmune diseases, ectopic pregnancy, and for the induction of medical abortions. It acts by inhibiting the metabolism of folic acid. Methotrexate...
was simultaneously marketed by the company during the same period. Aminopterin was discontinued by Lederle Laboratories in favor of methotrexate due to manufacturing difficulties of the former.
During the period Aminopterin was marketed, the agent was used off-label to safely treat over 4,000 patients with psoriasis in the United States, producing dramatic clearing of lesions.
The use of aminopterin in cancer treatment was supplanted in the 1950s by methotrexate
Methotrexate
Methotrexate , abbreviated MTX and formerly known as amethopterin, is an antimetabolite and antifolate drug. It is used in treatment of cancer, autoimmune diseases, ectopic pregnancy, and for the induction of medical abortions. It acts by inhibiting the metabolism of folic acid. Methotrexate...
due to the latter's better therapeutic index
Therapeutic index
The therapeutic index is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes death or toxicity ....
in a rodent tumor model. Now in a more pure preparation and supported by laboratory evidence of superior tumor cell uptake in vitro, aminopterin is being investigated in clinical trials in leukemia as a potentially superior antifolate to methotrexate.
The compound was explored as an abortifacient
Abortifacient
An abortifacient is a substance that induces abortion. Abortifacients for animals that have mated undesirably are known as mismating shots....
in the 1960s and earlier, but was associated with congenital malformations. Similar congenital abnormalities have been documented with methotrexate, and collectively their teratogenic effects have become known as the fetal aminopterin syndrome. When a similar cluster of abnormalies appears in the absence of exposure to antifolates it is referred to as aminopterin-like syndrome without aminopterin.
Although the use of aminopterin as a rodenticide is widely asserted on the web and elsewhere, there is no evidence that it has ever been used for that purpose either in the United States or elsewhere in the world. The preparation of the molecule is complex and expensive. It is also unstable in the environment due to degradation by light and heat. The apparently mistaken association of aminopterin with its use as a rodenticide likely dates back to a 1951 patent issued to the American Cyanamid Company (then the holding company of Lederle Laboratories) that is commonly cited by a variety of reference textbooks. Aminopterin has a single-dose LDLo
Lowest published lethal dose
In toxicology, the LDLo is the lowest dosage per unit of bodyweight of a substance known to have resulted in fatality in a particular animal species...
of 2.5 mg/kg when orally administered to rats.
Aminopterin and methotrexate
Methotrexate
Methotrexate , abbreviated MTX and formerly known as amethopterin, is an antimetabolite and antifolate drug. It is used in treatment of cancer, autoimmune diseases, ectopic pregnancy, and for the induction of medical abortions. It acts by inhibiting the metabolism of folic acid. Methotrexate...
are widely used in selection media (such as HAT medium
HAT medium
HAT Medium is a selection medium for mammalian cell culture, which relies on the combination of aminopterin, a drug that acts as a powerful folate metabolism inhibitor by inhibiting dihydrofolate reductase, with hypoxanthine and thymidine which are intermediates in DNA synthesis...
) for cell culture
Cell culture
Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...
.
Implication in 2007 Menu Foods recall
On March 23, 2007, ABC NewsABC News
ABC News is the news gathering and broadcasting division of American broadcast television network ABC, a subsidiary of The Walt Disney Company...
reported
that aminopterin was the chemical linked to the 2007 Menu Foods
Menu Foods
Menu Foods Limited, based in Streetsville in Mississauga, Ontario, Canada, and was the largest maker of wet cat and dog food in North America, with its products sold under 95 brand names, which the company identifies as supermarkets, big box and pet product retailers and wholesalers...
pet food contamination incident
2007 pet food recalls
The 2007 pet food recalls comprise the contamination and wide recall of many brands of cat and dog foods beginning in March 2007, and the ensuing developments involving the human food supply. The recalls in North America, Europe, and South Africa came in response to reports of renal failure in pets...
. The incident resulted in a massive recall of the affected foods. The link to aminopterin was confirmed by New York State Agriculture Commissioner Patrick Hooker and Dr. Donald Smith, Dean of Cornell University
Cornell University
Cornell University is an Ivy League university located in Ithaca, New York, United States. It is a private land-grant university, receiving annual funding from the State of New York for certain educational missions...
's College of Veterinary Medicine, in a statement released on the same day.
On March 27, the ASPCA Animal Poison Control Center expressed concern that the problem may not yet be fully understood and that other contaminants may be involved, noting that "clinical signs reported in cats affected by the contaminated foods are not fully consistent with the ingestion of rat poison containing aminopterin".
On March 30 it was widely reported that the United States Food and Drug Administration had found melamine
Melamine
Melamine is an organic base and a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 66% nitrogen by mass and, if mixed with resins, has fire retardant properties due to its release of nitrogen gas when burned or charred, and has several other industrial uses....
in wheat gluten that was used in the pet foods in question. These same reports stated that the FDA had failed to find evidence of aminopterin in the wheat gluten. Tests at the University of Guelph
University of Guelph
The University of Guelph, also known as U of G, is a comprehensive public research university in Guelph, Ontario, Canada. It was established in 1964 after the amalgamation of Ontario Agricultural College, the Macdonald Institute, and the Ontario Veterinary College...
in Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, Canada detected aminopterin in some pet food samples, but only in concentrations of parts per billion or parts per trillion, amounts too low to cause the symptoms seen.
Exposure and treatment
Symptoms of exposure in humans include:- nauseaNauseaNausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
- vomitingVomitingVomiting is the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose...
- anorexiaAnorexia (symptom)Anorexia is the decreased sensation of appetite...
- weight lossWeight lossWeight loss, in the context of medicine, health or physical fitness, is a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue and/or lean mass, namely bone mineral deposits, muscle, tendon and other connective tissue...
- chills
- feverFeverFever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
- stomatitisStomatitisStomatitis is an inflammation of the mucous lining of any of the structures in the mouth, which may involve the cheeks, gums, tongue, lips, throat, and roof or floor of the mouth...
– inflammation of the oral mucosaOral mucosaThe oral mucosa is the mucous membrane epithelium of the mouth. It can be divided into three categories.*Masticatory mucosa, para-keratinized stratified squamous epithelium, found on the dorsum of the tongue, hard palate and attached gingiva.... - pharyngitisPharyngitisPharyngitis is an inflammation of the throat or pharynx. In most cases it is quite painful, and is the most common cause of a sore throat.Like many types of inflammation, pharyngitis can be acute – characterized by a rapid onset and typically a relatively short course – or chronic....
– inflammation of the pharynxPharynxThe human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx... - erythematous rashesErythemaErythema is redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin. It occurs with any skin injury, infection, or inflammation...
– red rashes on the skin - hyperpigmentationHyperpigmentationIn dermatology, hyperpigmentation is the darkening of an area of skin or nails caused by increased melanin.-Causes:Hyperpigmentation may be caused by sun damage, inflammation, or other skin injuries, including those related to acne vulgaris...
– increased pigmentation associated with cleared psoriatic lesions - gastrointestinal hemorrhage
- renal failureRenal failureRenal failure or kidney failure describes a medical condition in which the kidneys fail to adequately filter toxins and waste products from the blood...
– in high doses necessarily involving concomitant leucovorin rescue - abortions in pregnant women
Supralethal doses of aminopterin may be rescued with the antidote Leucovorin (also known as folinic acid), a reduced
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
form 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...
which bypasses dihydrofolate reductase, the enzyme inhibited by aminopterin. Leucovorin has been used in rats, dogs and humans to rescue aminopterin toxicity. Leucovorin rescue is a therapeutic maneuver intentionally employed with antifolates to achieve tumoricidal drug concentrations that would otherwise be lethal to the patient.
In humans, leucovorin rescue at overdosages lower than 10 mg aminopterin in an average 70 kg adult should comprise an initial leucovorin dose of at least 20 mg (10.0 mg/m2), given intravenously (preferably), or orally. Subsequent doses of 20 mg (which may be taken orally) should be given at 6 hour intervals until hematological abnormalities are improved.
Massive aminopterin overdosage in humans (i.e. > 40 mg AMT in an average 70 kg adult), should be approached with an initial leucovorin dose of 100 mg (50 mg/m2), given intravenously and continued at 6 hour intervals until the hematological abnormalities are improved (likely 8–12 courses or more). Additionally, to prevent reversible aminopterin-mediated nephrotoxicity manifesting as increases in serum creatinine and which further delays drug elimination, urinary alkalinization with and volume expansion should be considered in cases of massive aminopterin overdosage, particularly those involving greater than 100 mg AMT in an average 70 kg adult human.
Consistent with the known enterohepatic cycling of the related antifolate methotrexate, oral activated charcoal, and saline cathartic
Cathartic
In medicine, a cathartic is a substance that accelerates defecation. This is in contrast to a laxative, which is a substance which eases defecation, usually by softening feces. It is possible for a substance to be both a laxative and a cathartic...
or sorbitol
Sorbitol
Sorbitol, also known as glucitol, Sorbogem® and Sorbo®, is a sugar alcohol that the human body metabolizes slowly. It can be obtained by reduction of glucose, changing the aldehyde group to a hydroxyl group. Sorbitol is found in apples, pears, peaches, and prunes...
may promote excretion if an overdose of aminopterin is suspected. However, rescue with leucovorin should form the backbone of treatment.
The vitamin folic acid is an oxidized precursor to reduced folates that is upstream of the blockade at dihydrofolate reductase, and compared to leucovrin is recognized as a very weak antidote to the toxic effects of antifolates that is inappropriate for use in cases of acute intoxication. Minnich et al. dosed mongrel dogs subcutaneously with aminopterin and folic acid simultaneously to test whether folic acid can rescue animals from the lethality and toxicity of aminopterin Dogs were given 0.020, 0.046, 0.044 escalated to 0.088, and 0.097 mg/kg aminopterin each day for 7 to 12 days. Folic acid was given in a weight ratio to aminopterin of 200:1 to 800:1. All animals survived. In contrast, animals given aminopterin in an amount of 0.041 mg/kg/day x 6 days without folic acid died. Thus, when the ratio of folic acid to aminopterin was 200:1 and greater, all of the subjects survived on regimens that would have otherwise been uniformly fatal to all subjects.
Similar effects have been noted in rodent species as well, where the range for rescue by folic acid was fairly narrow and highly dependent on the timing (optimal of 1 hour prior to aminopterin) of administration in relation to aminopterin. The temporal relationship between folic acid administration and rescue has been interpreted as the necessary period of time required for the vitamin to be converted in vivo to reduced forms.