Targeting methylguanine-DNA methyltransferase in the treatment of neuroblastoma.
OBJECTIVE
The combination of temozolomide and irinotecan has preclinical schedule-dependent synergy against neuroblastoma but is not curative for relapsed high-risk patients. We hypothesized that the DNA repair protein methylguanine-DNA methyltransferase (MGMT) is an important resistance factor, and that inactivation of MGMT would sensitize neuroblastoma cells to these agents.


METHODS
MGMT protein expression was assessed in 74 primary neuroblastoma tumors. Growth inhibition assays were done to determine the IC(50) and the extent of synergy observed with various concentrations of temozolomide, irinotecan, and the MGMT-inactivating agent O(6)-benzylguanine, using cultured syngeneic neuroblastoma cells with either low or high levels of MGMT expression. We then assessed efficacy in a mouse xenograft model of metastatic neuroblastoma.


RESULTS
MGMT was expressed by all 74 tumors evaluated. Pretreatment of neuroblastoma cells with O(6)-benzylguanine reduced the IC(50) of temozolomide by 10-fold regardless of level of MGMT expression, and pretreatment with BG followed by temozolomide + irinotecan further reduced the IC(50) in cells with high MGMT expression another 10-fold, to well below clinically achievable concentrations. The combination index was 0.27 to 0.30 for all three drugs in both cell lines, indicating strong synergy. Survival at 100 days for mice with metastatic neuroblastoma was 56% with three-drug treatment, compared with untreated controls (0%, P < 0.001) or temozolomide + irinotecan (10%, P = 0.081).


CONCLUSIONS
MGMT is widely expressed in primary neuroblastoma tumors, and is a relevant therapeutic target. Both in vitro and in vivo studies suggest inactivation of MGMT with O(6)-benzylguanine may increase the activity of temozolomide and irinotecan against neuroblastoma.
Wagner
Lars M
LM
Division of Pediatric Hematology/Oncology, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, Ohio 45229, USA. lars.wagner@cchmc.org
McLendon
Roger E
RE
Yoon
K Jin
KJ
Weiss
Brian D
BD
Billups
Catherine A
CA
Danks
Mary K
MK
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015254:DNA Modification Methylases / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000378:metabolism; D045643:DNA Repair Enzymes / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000378:metabolism; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006147:Guanine / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D000077146:Irinotecan; D051379:Mice; D016513:Mice, SCID; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000378:metabolism; D009447:Neuroblastoma / Q000201:enzymology* / Q000473:pathology; D009687:Nuclear Proteins / Q000378:metabolism; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D000972:Antineoplastic Agents, Phytogenic; D004791:Enzyme Inhibitors; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D025521:Tumor Suppressor Proteins; C064976:O(6)-benzylguanine; D006147:Guanine; D000077146:Irinotecan; D003606:Dacarbazine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D045643:DNA Repair Enzymes; D002166:Camptothecin; D000077204:Temozolomide