Division of Hematology-Oncology, MS#119, Childrens Hospital Los Angeles, 4650 Sunset Boulevard, Los Angeles, CA 90027, USA.
Br J Cancer. 2010 Oct 26;103(9):1369-79. doi: 10.1038/sj.bjc.6605927. Epub 2010 Oct 5.
The combination of temozolomide (TMZ) and irinotecan is a regimen used in neuroblastoma patients with recurrent disease. O(6)-methylguanine-DNA methyltransferase (MGMT) may have a function in resistance to TMZ. Using neuroblastoma pre-clinical models, we determined whether the inhibition of MGMT by O(6)-benzylguanine (O6-BG) could enhance the anti-tumour activity of TMZ and irinotecan.
The cytotoxicity of TMZ and irinotecan, either alone or in combination, was measured in five neuroblastoma cell lines in the presence or absence of O6-BG with a fluorescence-based cell viability assay (DIMSCAN). Anti-tumour activity was measured in three neuroblastoma xenograft models.
MGMT mRNA and protein were expressed in 9 out of 10 examined cell lines. Pretreatment of cells with 25 μM O6-BG decreased MGMT protein expression and enhanced The TMZ cytotoxicity by up to 0.3-1.4 logs in four out of five tested cell lines. TMZ (25 mg kg(-1) per day for 5 days every 3 weeks for four cycles) did not significantly improve mice survival, whereas the same schedule of irinotecan (7.5 mg kg(-1) per day) significantly improved survival (P<0.0001) in all three xenograft models. Combining O6-BG and/or TMZ with irinotecan further enhanced survival.
Our in vitro and in vivo findings suggest that irinotecan drives the activity of irinotecan and TMZ in recurrent neuroblastoma. Inhibitors of MGMT warrant further investigation for enhancing the activity of regimens that include TMZ.
替莫唑胺（TMZ）和伊立替康的联合方案用于治疗复发性神经母细胞瘤患者。O(6)-甲基鸟嘌呤-DNA 甲基转移酶（MGMT）可能在 TMZ 耐药中发挥作用。我们使用神经母细胞瘤临床前模型，确定 O(6)-苯甲基鸟嘌呤（O6-BG）对 MGMT 的抑制作用是否可以增强 TMZ 和伊立替康的抗肿瘤活性。
使用荧光细胞活力测定法（DIMSCAN），在存在或不存在 O6-BG 的情况下，测定 TMZ 和伊立替康单独或联合使用时对五种神经母细胞瘤细胞系的细胞毒性。在三种神经母细胞瘤异种移植模型中测量抗肿瘤活性。
在检查的 10 个细胞系中的 9 个中表达了 MGMT mRNA 和蛋白。用 25 μM O6-BG 预处理细胞可降低 MGMT 蛋白表达，并使四种测试细胞系中的四种细胞系中的 TMZ 细胞毒性增强多达 0.3-1.4 对数级。TMZ（25 mg/kg 每天，每 3 周连用 5 天，连用 4 个周期）并未显著改善小鼠的存活率，而相同方案的伊立替康（7.5 mg/kg 每天）在所有三种异种移植模型中均显著提高了存活率（P<0.0001）。将 O6-BG 和/或 TMZ 与伊立替康联合使用进一步提高了存活率。
我们的体外和体内研究结果表明，伊立替康驱动复发性神经母细胞瘤中伊立替康和 TMZ 的活性。MGMT 抑制剂值得进一步研究，以增强包括 TMZ 在内的方案的活性。
