Levetiracetam Sensitizes Glioblastoma Multiforme Cells to Temozolomide Plus Radiation Therapy

Abstract

Glioblastoma multiforme (GBM) is the most lethal brain cancer in adults. The maximum benefit from standard treatment, surgery plus radiation therapy (RT) with temozolomide (TMZ) has been shown in patients with the methylated O6-methylguanine-DNA-methyltransferase (MGMT) gene. Levetiracetam (Keppra), a third generation anticonvulsant, has been reported as inhibitor of cellular MGMT expression. We investigate the effect of Levetiracetam on RT+TMZ treatment in vitro and speculate on its possible clinical relevance. Three MGMT(+) cell lines (LN18, HCT116, H1299) were used to evaluate the effects of Levetiracetam on MGMT expression. The effects of Levetiracetam on the TMZ induced radiosensitization of LN18 and MGMT(-) U251 GBM cell lines were evaluated according to clonogenic assay and γH2AX expression. With data from 58 GBM patients, enrolled at NCI, we then retrospectively assessed the relationship between Levetiracetam treatment and clinical outcome. Levetiracetam exposure reduced MGMT expression in all three MGMT(+) cells. Specifically, exposure of LN18 to 50μM of Levetiracetam for 1 hour resulted in decreased MGMT expression that lasted 6 hours. Clonogenic analysis indicated that TMZ enhanced the radiosensitivity of the MGMT(+) LN18 with a DEF (at a surviving fraction of 0.1) of 1.28; addition of Levetiracetam increased the DEF to 1.51. In contrast, the DEFs for the MGMT(-) U251 cells were 1.34 and 1.36 for TMZ alone and Levetiracetam+TMZ, respectively. The number of γH2AX foci, a marker of DNA-DSBs, remaining at 24 hours post-irradiation was significantly increased in LN18 with RT+TMZ+Levetiractam as compared to RT+TMZ. A total of 58 patients were evaluated with median follow-up of 16 months (range, 2∼53 months). Overall survival was 27 months with Levetiracetam and RT+TMZ treatment (45 patients) and 18 months with RT+TMZ treatment (13 patients) (p = 0.63). However, progression-free survival was 4 and 11 months with RT+TMZ and RT+TMZ+Levetiracetam (p = 0.03), respectively. In vitro data indicate that Levetiracetam can enhance TMZ-induced radiosensitization in an MGMT(+) GBM cell line. Pilot clinical data suggest that Levetiracetam along with RT+TMZ may increase survival in GBM patients. Further investigation is needed to confirm these results.