Nimotuzumab enhances temozolomide‐induced growth suppression of glioma cells expressing mutant EGFR in vivo

Abstract A mutant form of epidermal growth factor receptor ( EGFR ), EGFR v III , is common in glioblastoma ( GBM ) and confers enhanced tumorigenic activity and drug resistance. Nimotuzumab, an anti‐ EGFR antibody, has shown preclinical and clinical activity to GBM , but its specific activity against EGFR v III has not been fully investigated. Human glioma U87 MG or LNZ 308 cells overexpressing either wild‐type (wt) EGFR or EGFR v III were treated with nimotuzumab, temozolomide, or both. Expression and phosphorylation status of molecules were determined by Western blot analysis. Methylation status of promoter region of O 6 ‐methylguanine‐ DNA methyltransferase ( MGMT ) was detected by methylation‐specific PCR . Antitumor activity was tested using nude mice bearing either subcutaneous or intracerebral xenografts along with analyses of EGFR phosphorylation status, proliferation, apoptosis, and vessel density. Nimotuzumab treatment resulted in reduction of EGFR v III tyrosine phosphorylation with a decrease in Akt phosphorylation that was greater than that of wt EGFR . Correspondingly, antitumor effects, growth suppression and survival elongation, were more significant in mice bearing either subcutaneous or intracerebral tumor expressing EGFR v III than in those expressing wt EGFR . These effects were markedly increased when temozolomide was combined with nimotuzumab. The post‐treatment recurrent brain tumors exhibited a decrease in expression of the mismatch repair ( MMR ) proteins, MSH 6 and MLH 1, but their methylated MGMT status did not changed. Nimotuzumab has in vivo antitumor activity against GBM , especially those expressing EGFR v III , when combined with temozolomide. This could provide a basis for preselection of patients with GBM by EGFR status who might benefit from the nimotuzumab and temozolomide combination therapy.