Semustine

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Semustine
Semustine.svg
Clinical data
ATC code
Identifiers
  • 1-(2-Chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea
CAS Number
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Chemical and physical data
Formula C10H18ClN3O2
Molar mass 247.72 g·mol−1
3D model (JSmol)
  • CC1CCC(CC1)NC(=O)N(CCCl)N=O
  • InChI=1S/C10H18ClN3O2/c1-8-2-4-9(5-3-8)12-10(15)14(13-16)7-6-11/h8-9H,2-7H2,1H3,(H,12,15) X mark.svgN
  • Key:FVLVBPDQNARYJU-UHFFFAOYSA-N X mark.svgN
 X mark.svgNYes check.svgY  (what is this?)    (verify)

Semustine (1- (2-Chloroethyl)-3-(trans-4-methylcyclohexyl)- 1-nitrosourea, MeCCNU) is an alkylating nitrosourea compound used in chemotherapy treatment of various types of tumours. [1] [2] Due to its lipophilic property, semustine can cross the blood-brain barrier for the chemotherapy of brain tumours, where it interferes with DNA replication in the rapidly-dividing tumour cells. [2] Semustine, just as lomustine, is administered orally. Evidence has been found that treatment with semustine can cause acute leukaemia as a delayed effect in very rare cases. [3]

Contents

Structure and reactivity

Semustine (Me-CCNU) is an organochlorine compound that is urea in which the two hydrogens on one of the amino groups are replaced by nitroso and 2-chloroetyl groups and one hydrogen from the other amino group is replaced by a 4-methylcyclohexcyl group. Semustine is also known as a 4-methyl derivative of lomustine. [4] [5]

Synthesis

The synthesis of semustine originates from a systematic synthesis scheme revolving around N-Nitrosourea compounds. [6] [7] Phosgene is reacted with Aziridine to produce the chemical intermediate di(aziridin-1-yl) methanone. This reacts with the subsequently released HCl from the production of the intermediate to open the Aziridine rings and it will form 1,3-bis(2-chloroethyl)-urea. The next step is to nitrosate this compound with the sodium nitrite in formic acid. This will give one of the nitrogen’s a nitroso functional group. With this step carmustine (BCNU), another medication used for chemotherapy, is formed. BCNU is subsequently decomposed in the presence of 4-Methylcyclohexylamine. The aliphatic amine is in two equivalents present during the decomposition. During the decomposition, the compound loses its nitroso group and only one methyl cyclohexyl group will be found on the compound. The final step is to repeat the nitrosation of the compound under the same conditions and Semustine (Me-CCNU) is synthesised. This whole synthesis is shown in Figure 1.

More recent studies suggest using 1-chloro-2-isocyanatoethyl as a starting material alongside cyclohexylamine. For this, TEA can be used as a catalyst to get to the same final step as the previously mentioned synthesis route. In this final step, the nitrosation can be done again with sodium nitrite (1) or with tert-Butyl nitrite (2). [8] [9] In this synthesis R = H, CH3 or OH. This whole synthesis is shown in Figure 2.

Available forms

Since the synthesis yields a stable substance, this compound is usually delivered as pure substance and not as a salt. When supplied as medicine, the most common forms of administration are pills with a range from 3.0 to 100 mg semustine per pill. [8]

Mechanism of action

DNA is the most significant part of the cell, performing the most important processes, replication, and transcription. These processes and DNA itself can be targeted with small molecules or ligands with possible antitumor activity, resulting in prevention of continuous growth and proliferating of cancer cells. [2] [10] The common property of alkylating agents, including semustine, is their capacity to become very strong electrophiles through the formation of (chloro-) carbonium ion intermediates, which are products of the hydrolysis of the semustine drug. This reaction yields covalent cross-links between various nucleophilic DNA bases by alkylation, causing denaturation of the double helix [11] [12] and inhibiting separation of the DNA strand. By this mechanism, semustine interferes with rapidly proliferating cells and exerts its anti-tumour effects. [10] [13] Targets of the interstrand cross-link forming are specifically the N-7 of guanine, O-6 of adenine and other sites on the purine bases. [13] This is depicted in Figure 3. The electrophilic property of semustine increases under acidic conditions, which makes the nucleophilic attack occur much faster. In general, acidic pH conditions cause a significant increase in the reaction rate of the semustine drug. [10]

Metabolism

After oral administration and absorption from the gastrointestinal tract, semustine undergoes rapid chemical decomposition and oxidative metabolism. Due to the lipophilic nature of semustine, the distribution is quickly across the tissue. [11] [14] Semustine is metabolised by the cytochrome P450 (CYP) mono-oxygenase system on the cyclohexyl ring carbons and the 2-chloroethyl sidechain resulting hydroxylated metabolites, which remains alkylating and anti-tumour active. Most of the biological effect is due to the generation of the chloroethyl carbonium ion from the ring hydroxylated metabolite. Ring hydroxylation occurs during the “first pass” through the gut wall and liver. [15] The metabolites and decomposition products are excreted by the kidneys into the urine. Up to 60% of the dose is excreted by urine within 48 hours. [16] The decomposition products present in the urine are cis-3-hydroxy-trans-4-methylcyclohexylamine, trans-4-methylcyclohexylamine, trans-4-hydroxymethylcyclohexylamine and trans-3-hydroxy-trans-4-methyl-cyclohexylamine. [17] These are shown in Figure 4.

Indications

Nitrosoureas such as semustine frequently cause nausea and vomiting, after admission (4 to 6 hours). The major toxic effects of semustine are thrombocytopenia and leukopenia caused by cumulative doses. Secondly the nephrotoxicity and hepatotoxicity of the semustine cause pulmonary fibrosis and renal dysfunction. Semustine nephrotoxicity is cumulative, the cumulative dose at which nephrotoxicity is likely to occur has been estimated to be near 2,000 mg/m2. This problem generally appears only in patients being treated for more than 1 year, which requires a prolonged survival time. [18]

Efficacy and side effects

Efficacy

Semustine was used to treat several different types of cancers. The main one was L1210 leukaemia and Hodgkin lymphoma. Other types are metastatic brain tumours, Lewis lung tumours, cancers of the digestive tract, lymphoma, malignant melanoma, and epidermoid carcinoma of the lung. [19] It has however not shown desired results as an antineoplastic drug and thus has never been approved for it. Combinations with other drugs have also been done in the 70’s but have not shown more beneficial results. [20] In China, research is still done on the compound. These however also state the need for further investigation and possible different combinations of antineoplastic drugs to get a higher rate of complete response and overall survival after treatment. [21]

Adverse effects

During the trials of semustine, sufficient evidence was found that semustine is a carcinogen. During a trail of 2067 patients, 14 cases of acute leukaemia were found. This was combined with a roughly 4% chance to acquire leukaemia disorder within six years. [3] This trail was done on patients with gastrointestinal cancer and before the use of this antineoplastic drug, there were no recorded cases in the medical history of Connecticut that these combinations of cancer occur. This could be derived back to the start of the nitrosourea chemotherapy. [3] Providing quantitative evidence that semustine is a carcinogen. [22] For this reason it is also added to IARC group 1 for carcinogenic agents to humans.

Effects on animals

The described carcinogenicity of semustine to humans has not been found in animals, specifically mice and rats. It is however still a carcinogen. There was an increase found in peritoneal sarcoma and lung tumours, indicating a different toxicity to animals. [19] [20]

Related Research Articles

<span class="mw-page-title-main">Chemotherapy</span> Treatment of cancer using drugs that inhibit cell division or kill cells

Chemotherapy is a type of cancer treatment that uses one or more anti-cancer drugs as part of a standardized chemotherapy regimen. Chemotherapy may be given with a curative intent or it may aim to prolong life or to reduce symptoms. Chemotherapy is one of the major categories of the medical discipline specifically devoted to pharmacotherapy for cancer, which is called medical oncology.

<span class="mw-page-title-main">Alkylation</span> Transfer of an alkyl group from one molecule to another

Alkylation is a chemical reaction that entails transfer of an alkyl group. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene. Alkylating agents are reagents for effecting alkylation. Alkyl groups can also be removed in a process known as dealkylation. Alkylating agents are often classified according to their nucleophilic or electrophilic character. In oil refining contexts, alkylation refers to a particular alkylation of isobutane with olefins. For upgrading of petroleum, alkylation produces a premium blending stock for gasoline. In medicine, alkylation of DNA is used in chemotherapy to damage the DNA of cancer cells. Alkylation is accomplished with the class of drugs called alkylating antineoplastic agents.

Substances, mixtures, and exposure circumstances in this list have been classified as group 1 by the International Agency for Research on Cancer (IARC): The agent (mixture) is carcinogenic to humans. The exposure circumstance entails exposures that are carcinogenic to humans. This category is used when there is sufficient evidence of carcinogenicity in humans. Exceptionally, an agent (mixture) may be placed in this category when evidence of carcinogenicity in humans is less than sufficient but there is sufficient evidence of carcinogenicity in experimental animals and strong evidence in exposed humans that the agent (mixture) acts through a relevant mechanism of carcinogenicity.

The agents in this list have been classified in group 2A by the International Agency for Research on Cancer (IARC). The term "agent" encompasses both substances and exposure circumstances that pose a risk. This designation is applied when there is limited evidence of carcinogenicity in humans as well as sufficient evidence of carcinogenicity in experimental animals. In some cases, an agent may be classified in this group when there is inadequate evidence of carcinogenicity in humans along with sufficient evidence of carcinogenicity in experimental animals and strong evidence that the carcinogenesis is mediated by a mechanism that also operates in humans. Exceptionally, an agent may be classified in this group solely on the basis of limited evidence of carcinogenicity in humans.

<span class="mw-page-title-main">History of cancer chemotherapy</span>

The era of cancer chemotherapy began in the 1940s with the first use of nitrogen mustards and folic acid antagonist drugs. The targeted therapy revolution has arrived, but many of the principles and limitations of chemotherapy discovered by the early researchers still apply.

<span class="mw-page-title-main">Procarbazine</span> A chemotherapy medication used for several cancer types

Procarbazine is a chemotherapy medication used for the treatment of Hodgkin's lymphoma and brain cancers. For Hodgkin's it is often used together with chlormethine, vincristine, and prednisone while for brain cancers such as glioblastoma multiforme it is used with lomustine and vincristine. It is typically taken by mouth.

<span class="mw-page-title-main">Nitrogen mustard</span> Family of chemical compounds

Nitrogen mustards are cytotoxic organic compounds with the chloroethylamine ((ClCH2)2NR2) functional group. Although originally produced as chemical warfare agents, they were the first chemotherapeutic agents for treatment of cancer. Nitrogen mustards are nonspecific DNA alkylating agents.

<span class="mw-page-title-main">Melphalan</span> Chemical compound

Melphalan, sold under the brand name Alkeran among others, is a chemotherapy medication used to treat multiple myeloma, ovarian cancer, melanoma, and AL amyloidosis. It is taken by mouth or by injection into a vein.

<span class="mw-page-title-main">Teniposide</span> Chemical compound

Teniposide is a chemotherapeutic medication used in the treatment of childhood acute lymphocytic leukemia (ALL), Hodgkin's lymphoma, certain brain tumours, and other types of cancer. It is in a class of drugs known as podophyllotoxin derivatives and slows the growth of cancer cells in the body.

<span class="mw-page-title-main">Busulfan</span> Chemical compound

Busulfan is a chemotherapy drug in use since 1959. It is a cell cycle non-specific alkylating antineoplastic agent, in the class of alkyl sulfonates. Its chemical designation is 1,4-butanediol dimethanesulfonate.

<span class="mw-page-title-main">Streptozotocin</span> Chemical compound

Streptozotocin or streptozocin (STZ) is a naturally occurring alkylating antineoplastic agent that is particularly toxic to the insulin-producing beta cells of the pancreas in mammals. It is used in medicine for treating certain cancers of the islets of Langerhans and used in medical research to produce an animal model for hyperglycemia and Alzheimer's in a large dose, as well as type 2 diabetes or type 1 diabetes with multiple low doses.

<span class="mw-page-title-main">Nitrosourea</span> Chemical compound

Nitrosourea is both the name of a molecule, and a class of compounds that include a nitroso (R-NO) group and a urea.

<span class="mw-page-title-main">Lomustine</span> Chemical compound

Lomustine (INN); abbreviated as CCNU; original brand name CeeNU, now marketed as Gleostine) is an alkylating nitrosourea compound used in chemotherapy. It is closely related to semustine and is in the same family as streptozotocin. It is a highly lipid-soluble drug, thus it crosses the blood–brain barrier. This property makes it ideal for treating brain tumors, which is its primary use, although it is also used to treat Hodgkin lymphoma as a second-line option. It has also been used in veterinary practice as a treatment for cancers in cats and dogs.

<span class="mw-page-title-main">Carmustine</span> Chemical compound

Carmustine, sold under the brand name BiCNU among others, is a medication used mainly for chemotherapy. It is a nitrogen mustard β-chloro-nitrosourea compound used as an alkylating agent.

An alkylating antineoplastic agent is an alkylating agent used in cancer treatment that attaches an alkyl group (CnH2n+1) to DNA.

<span class="mw-page-title-main">Chlornaphazine</span> Chemical compound

Chlornaphazine, a derivative of 2-naphthylamine, is a nitrogen mustard that was developed in the 1950s for the treatment of polycythemia and Hodgkin's disease. However, a high incidence of bladder cancers in patients receiving treatment with chlornaphthazine led to use of the drug being discontinued.

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References

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