RESUMO
Although temozolomide has shown clinical activity against neuroblastoma, this activity is likely limited by the DNA repair enzyme O6-methylguanine DNA methyltransferase (MGMT). We hypothesized that IFN-beta 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-beta 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-beta 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-beta 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-beta 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-beta); 352 +/- 110%, P = 0.0001 (combo)] and disseminated [bioluminescent signal: control (1.32e10 +/- 6.5e9) versus IFN-beta (2.78e8 +/- 3.09e8), P = 0.025, versus temozolomide (2.06e9 +/- 1.55e9), P = 0.1, versus combination (2.13e7 +/- 7.67e6), P = 0.009]. IFN-beta appears to sensitize neuroblastoma cells to the cytotoxic effects of temozolomide through attenuation of MGMT expression. Thus, IFN-beta and temozolomide may be a useful combination for treating children with this difficult disease.
