Next, we examined whether O6-BG can increase the activity of TMZ or the TMZ and irinotecan combination in neuroblastomas using three drug-sensitive (CHLA-15, CHLA-42 and SMS-KCNR) and two multidrug-resistant (CHLA-90 and CHLA-136) cell lines, including the one that does not express MGMT (CHLA-90) (Figures 2 and 3). This evidence concerns the gene MGMT and neuroblastoma.