Activity of temozolomide in the treatment of central nervous system tumor xenografts.

The activity of 8-carbamoyl-3-methylimidazo[5,1-d]-1,2,3,5-tetrazin- 4(3H)-one (temozolomide) in the treatment of a panel of xenografts derived from ependymoma, medulloblastoma, and childhood and adult high-grade glioma was evaluated in athymic nude mice bearing s.c. and intracranial tumors. Temozolomide administered daily for a total of five doses demonstrated marked activity against a panel of Mer+ xenografts despite marginal to moderate activity of 1,3-bis(2-chloroethyl)-1-nitrosourea. The growth delays produced by temozolomide in these xenografts were 1.8-7.5-fold greater than those produced by procarbazine. Although temozolomide demonstrated marginal activity against the Mer+ cell line D341 Med when a 5-day schedule was used, a high-dose 1-day schedule resulted in moderate activity. Temozolomide produced increases in median survival of 1285% (adult glioma D-54 MG), 323% (childhood glioma D-456 MG), and 68% (ependymoma D612 EP). Pretreatment of mice with O6-benzylguanine increased temozolomide-induced mortality, requiring reduction of the dosage from 1200 to 750 mg/m2 on the single-day regimen. O6-Benzylguanine pretreatment of mice bearing Mer+ D341 Med increased the growth delay of temozolomide, in duplicate experiments, from -3.1 to 4.8 and 1.1 to 4.9 days. These studies suggest that temozolomide may be active in the treatment of a broad spectrum of central nervous system cancers, including Mer+ tumors resistant to 1,3-bis(2-chloroethyl)-1-nitrosourea.