Temozolomide (TMZ) is a methylating agent which prolongs survival when administered during and after radiotherapy in the first-line treatment of glioblastoma and which also has significant activity in recurrent disease. O 6 -methylguanine DNA methyltransferase (MGMT) is a DNA repair enzyme attributed a role in cancer cell resistance to O 6 -alkylating agent-based chemotherapy. Using a panel of 12 human glioma cell lines, we here defined the sensitivity to TMZ in acute cytotoxicity and clonogenic survival assays in relation to MGMT, mismatch repair and p53 status and its modulation by dexamethasone, irradiation and BCL-X L . We found that the levels of MGMT expression were a major predictor of TMZ sensitivity in human glioma cells. MGMT activity and clonogenic survival after TMZ exposure are highly correlated (p < 0.0001, r 2 ¼ 0.92). In contrast, clonogenic survival after TMZ exposure does not correlate with the expression levels of the mismatch repair proteins mutS homologue 2, mutS homologue 6 or post-meiotic segregation increased 2. The MGMT inhibitor O 6 -benzylguanine sensitizes MGMT-positive glioma cells to TMZ whereas MGMT gene transfer into MGMT-negative cells confers protection. The antiapoptotic BCL-X L protein attenuates TMZ cytotoxicity in MGMT-negative LNT-229 but not in MGMT-positive LN-18 cells. Neither ionizing radiation (4 Gy) nor clinically relevant concentrations of dexamethasone modulate MGMT activity or TMZ sensitivity. Abrogation of p53 wild-type function strongly attenuates TMZ cytotoxicity. Conversely, p53 mimetic agents designed to stabilize the wild-type conformation of p53 sensitize glioma cells for TMZ cytotoxicity. Collectively, these results suggest that the determination of MGMT expression and p53 status will help to identify glioma patients who will or will not respond to TMZ. Keywords: BCL-X L , glioblastoma, O 6 -methylguanine DNA methyltransferase, p53, temozolomide. Temozolomide (TMZ) is a cytotoxic alkylating agent which has shown activity in recurrent anaplastic glioma and glioblastoma (Yung et al. 1999(Yung et al. , 2000. Moreover, the recent European Organisation for Research and Treatment of Cancer/National Cancer Institute of Canada trial on concomitant and adjuvant TMZ in addition to radiotherapy as the first-line treatment of glioblastoma produced an increase in median survival from 12.1 to 14.6 months and an increase in the 2-year survival rate from 10 to 26% compared with radiotherapy alone (Stupp et al. 2005).Temozolomide is rapidly and completely absorbed after oral administration and undergoes spontaneous hydrolysis at physiological pH to its active metabolite 5-(3-methyltriazeno)-imidazole-4-carboxamide. 5-(3-methyltriazeno)-imidazole-4-carboxamide causes DNA damage by methylation of the O 6 position of guanine. However, DNA adducts different from O 6 -methylguanine might also be involved in the cytotoxicity induced by methylating agents and poly (ADP-ribose) polymerase (PARP) inhibitors may also sensitize tumour cells to TMZ-induced cell death (Tentori e...

Picard, M; Weller, M (2010). Phase I/IIa study of cilengitide and temozolomide with concomitant radiotherapy followed by cilengitide and temozolomide maintenance therapy in patients with newly diagnosed glioblastoma. Patients and MethodsPatients (≥18 to ≤70 years) were treated with cilengitide (500 mg) administered twice weekly i.v. in addition to standard radiotherapy with comcomitant and adjuvant temozolomide. Treatment was continued until disease progression or for a maximum of 35 weeks. The primary endpoint was progression-free survival (PFS) at 6 months. ResultsFifty-two patients (median age 57 years; 62% male) were included. Six-and 12-month PFS rates were 69% (95% confidence interval [CI], 54-80%) and 33% (95% CI, 21-46%). Median PFS was 8 months (95% CI, 6.0-10.7). Twelve-and 24-month overall survival (OS) rates were 68% (95% CI, 53-79%) and 35% (95% CI, 22-48%). Median ConclusionCompared with historical controls, the addition of concomitant and adjuvant cilengitide to standard chemoradiation demonstrated promising activity in patients with glioblastoma with MGMT promoter methylation.5