gms | German Medical Science

Objective: Human glioblastoma multiforme (GBM) has a poor prognosis and several new target drugs were not able to improve survival. Drug resistance through the expression of O6-methylguanine methyltransferase (MGMT) is one mechanism that is associated with temozolomide (TMZ) resistance and poor outcome. For other tumor entities such as melanoma it has been shown that hyperthermia can increase TMZ sensitivity. The aim of this study was to evaluate the effects of additional hyperthermia on human GBM specimens in vitro.

Methods: Human GBM specimens from 18 patients were cultured and incubated with 150 µmol TMZ for 72 hours (h). Hyperthermia (43°) was induced after TMZ incubation for 1h. Cell proliferation was measured using an MTT assay. Viable cells were calculated for TMZ in combination with hyperthermia at 72h and compared to TMZ effects without hyperthermia. Gene expression of downstream pathways was quantified by real-time PCR.

Results: After 72h TMZ reduced viable cells to less than 69.6%% in MGMT-methylated GBM specimens and to 92.9% in MGMT-unmethylated GBM specimens (P<0.001). With additional hyperthermia viable cells for MGMT-methylated and MGMT-unmethylated GBM specimens were 70.8% and 80.9%, respectively. The total reduction in viable cells with additional hyperthermia compared to normothermia was +1.2% for MGMT-methylated and –12.0% (P=0.025) for MGMT-unmethylated GBM specimens. Downregulation of p53 expression was found in MGMT-unmethylated GBM specimens after hyperthermia and TMZ incubation (1.80; IQR 0.88-6.18) compared to TMZ incubation alone (4.82; IQR 1.86-105.78).

Conclusion: In vitro the addition of hyperthermia treatment increases TMZ-induced cell death in MGMT-umethylated GBM specimens. Furthermore, the downregulation of p53 expression in MGMT-unmethylated specimens could support the hypothesis that hyperthermia increases TMZ induced apoptosis. No significant additional effect was seen in MGMT-methylated specimens.