Temozolomide

Systematic (IUPAC) name
4-methyl-5-oxo- 2,3,4,6,8-pentazabicyclo [4.3.0] nona-2,7,9-triene- 9-carboxamide
Identifiers
CAS number	85622-93-1
ATC code	L01AX03
PubChem	CID 5394
DrugBank	APRD00557
Chemical data
Formula	C6H6N6O2
Mol. mass	194.151 g/mol
Pharmacokinetic data
Protein binding	15%
Metabolism	spontaneously hydrolyzed at physiologic pH to the active species, 3-methyl-(triazen-1-yl)imidazole-4-carboxamide (MTIC) and to temozolomide acid metabolite.
Half-life	1.8 hours
Therapeutic considerations
Pregnancy cat.	?
Legal status	?-only (US)
Routes	Oral
Y(what is this?)  (verify)

Temozolomide (brand names Temodar and Temodal Schering-Plough Corporation) is an oral alkylating agent which can be used for the treatment of Grade IV astrocytoma -- an aggressive brain tumor, also known as glioblastoma multiforme as well as Melanoma, a form of skin cancer. It is also indicated for Grade III Anaplastic Astrocytoma and not indicated for, but now used to treat oligodendroglioma brain tumors in some countries, replacing the older (and less well-tolerated) PCV (Procarbazine-Lomustine-Vincristine) regimen. The agent was developed by Malcolm Stevens and his team at Aston University in Birmingham,^[1] A derivative of imidazotetrazine, temozolomide is the prodrug of MTIC (3-methyl-(triazen-1-yl)imidazole-4-carboxamide). It has been available in the US since August 1999, and in other countries since the early 2000s.

The therapeutic benefit of temozolomide depends on its ability to alkylate/methylate DNA, which most often occurs at the N-7 or O-6 positions of guanine residues. This methylation damages the DNA and triggers the death of tumor cells. However, some tumor cells are able to repair this type of DNA damage, and therefore diminish the therapeutic efficacy of temozolomide, by expressing an enzyme called O-6-methylguanine-DNA methyltransferase (MGMT) or O-6-alkylguanine-DNA alkyltransferase (AGT or AGAT).^[2] In some tumors, epigenetic silencing of the MGMT/AGT gene prevents the synthesis of this enzyme, and as a consequence such tumors are more sensitive to killing by temozolomide.^[3] Conversely, the presence of MGMT protein in brain tumors predicts poor response to temozolomide and these patients receive little benefit from chemotherapy with temozolomide.^[4]

[edit] Indications

Nitrosourea- and procarbazine-refractory anaplastic astrocytoma

Newly-diagnosed glioblastoma multiforme

Temozolomide (sometimes referred to as TMZ) is an imidazotetrazine derivative of the alkylating agent dacarbazine. It undergoes rapid chemical conversion in the systemic circulation at physiological pH to the active compound, MTIC (monomethyl triazeno imidazole carboxamide). Temozolomide exhibits schedule-dependent antineoplastic activity by interfering with DNA replication. Temozolomide has demonstrated activity against recurrent glioma. In a recent randomized trial, concomitant and adjuvant temozolomide chemotherapy with radiation significantly improves progression free survival and overall survival in glioblastoma multiforme patients.

The most common non-hematological adverse effects associated with temozolomide were nausea and vomiting and were either self-limiting or readily controlled with standard antiemetic therapy. These effects were usually mild to moderate (grade 1 to 2). The incidence of severe nausea and vomiting is around 4% each. Patients who have pre-existing or a history of severe vomiting may require antiemetic therapy before initiating temozolomide treatment. Temozolomide should be administered in the fasting state, at least one hour before a meal. Capsules must not be opened or chewed, but are to be swallowed whole with a glass of water. Antiemetic therapy may be administered prior to, or following, administration of temozolomide. Temozolomide is contraindicated in patients with hypersensitivity to its components or to dacarbazine. The use of temozolomide is not recommended in patients with severe myelosuppression. Temozolomide is genotoxic, teratogenic and fetotoxic and should not be used in pregnancy. Nursing should be discontinued while receiving the drug because of the risk of secretion into breast milk. In male patients, temozolomide can have genotoxic effects. Men are advised not to father a child during or up to six months after treatment and to seek advice on cryoconservation of sperm prior to treatment, because of the possibility of irreversible infertility due to temozolomide therapy.

TEMOZM

[edit] Formulations

Temozolomide is available in the United States in 5 mg, 20 mg, 100 mg, 140 mg, 180 mg & 250 mg capsules. Now also available in an IV form for people who can not swallow capsules or who have insurance that does not cover oral cancer agents!

[edit] Further improvement of anticancer potency

Laboratory studies and clinical trials are investigating whether it might be possible to further increase the anticancer potency of temozolomide by combining it with other pharmacologic agents. For example, clinical trials have indicated that the addition of chloroquine might be beneficial for the treatment of glioma patients.^[5] In laboratory studies, it was found that temozolomide killed brain tumor cells more efficiently when epigallocatechin gallate (EGCG), a component of green tea, was added; however, the efficacy of this effect has not yet been confirmed in brain tumor patients.^[6]

Because tumor cells that synthesize the MGMT/AGT enzyme are more resistant to killing by temozolomide, it was investigated whether the inclusion of O-6-benzylguanine (O6-BG), an inhibitor of MGMT, would be able to overcome this resistance and improve the drug's therapeutic effectiveness. In the laboratory, this combination indeed showed increased activity in tumor cell culture in vitro and in animal models in vivo.^[7] However, a recently completed phase II clinical trial with brain tumor patients yielded mixed outcomes; while there was some improved therapeutic activity when O6-BG and temozolomide were given to patients with temozolomide-resistant anaplastic glioma, there seemed to be no significant restoration of temozolomide sensitivity in patients with temozolomide-resistant glioblastoma multiforme.^[8]

There are also efforts to engineer hematopoietic stem cells to carry MGMT prior to transplanting them into brain tumor patients. This would allow for the patients to receive stronger doses of temozolomide, since the patient's hematopoietic cells would be resistant to the drug. ^[9]

High - doses of temozolomide in high - grade gliomas yeld low toxicity but the results are comparable to the standard doses. ^[10]

[edit] See also

• treatment of glioblastoma multiforme
• glioblastoma multiforme
• astrocytoma

[edit] References

[edit] External links

• Chemotherapy Drug Shrinks Brain Tumors American Academy of Neurology, May 21, 2007

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Temozolomide".