IFN-β sensitizes neuroblastoma to the antitumor activity of temozolomide by modulating O6-methylguanine DNA methyltransferase expression

Although temozolomide has shown clinical activity against neuroblastoma, this activity is likely limited by the DNA repair enzyme O 6 -methylguanine DNA methyltransferase (MGMT). We hypothesized that IFN-β could sensitize neuroblastoma cells to the cytotoxic effects of temozolomide through its ability to down-regulate MGMT expression. In vitro proliferation of three neuroblastoma cell lines treated with IFN-β and temozolomide alone or in combination was examined. Antitumor activity was assessed in both localized and disseminated neuroblastoma xenografts using single-agent and combination therapy, with continuous delivery of IFN-β being established by a liver-targeted adeno-associated virus-mediated approach. Two neuroblastoma cell lines (NB-1691 and SK-N-AS) were found to have high baseline levels of MGMT expression, whereas a third cell line (CHLA-255) had low levels. Temozolomide had little effect on in vitro proliferation of the neuroblastoma cell lines with high MGMT expression, but pretreatment with IFN-β significantly decreased MGMT expression and cell counts (NB-1691: 36 ± 3% of control, P = 0.0008; SK-N-AS: 54 ± 7% control, P = 0.003). In vivo , NB-1691 tumors in CB17-SCID mice treated with the combination of IFN-β and temozolomide had lower MGMT expression and a significantly reduced tumor burden, both localized [percent initial tumor volume: 2,516 ± 680% (control) versus 1,272 ± 330% (temozolomide), P = 0.01; 1,348 ± 220%, P = 0.03 (IFN-β); 352 ± 110%, P = 0.0001 (combo)] and disseminated [bioluminescent signal: control (1.32e 10 ± 6.5e 9 ) versus IFN-β (2.78e 8 ± 3.09e 8 ), P = 0.025, versus temozolomide (2.06e 9 ± 1.55e 9 ), P = 0.1, versus combination (2.13e 7 ± 7.67e 6 ), P = 0.009]. IFN-β appears to sensitize neuroblastoma cells to the cytotoxic effects of temozolomide through attenuation of MGMT expression. Thus, IFN-β and temozolomide may be a useful combination for treating children with this difficult disease. [Mol Cancer Ther 2008;7(12):3852–8]