Temozolomide

Refractory anaplastic astrocytoma (WHO grade III) and Glioblastoma multiforme (WHO grade IV) are primary malignant brain tumours with poor prognosis and limited treatment options. Despite considerable genetic heterogeneity, these tumours often have impaired DNA repair systems, rendering them initially sensitive to alkylating agents, although they invariably develop resistance to these agents over time. Temozolomide is an imidazotetrazine prodrug that is stable at acidic pH but undergoes spontaneous nonenzymatic hydrolysis at neutral or slightly basic pH; these properties allow for both oral and intravenous administration. Following initial hydrolysis, further reactions liberate a highly reactive methyl diazonium cation capable of methylating various residues on adenosine and guanine bases leading to DNA lesions and eventual apoptosis. Temozomolide as an adjunct to radiotherapy followed by maintenance dosing remains the standard of care for both Glioblastoma and refractory anaplastic astrocytoma.

Temozolomide was granted FDA approval on August 11, 1999, as an oral capsule and subsequently on February 27, 2009, as an intravenous injection. It is currently marketed under the trademark TEMODAR® by Merck.