Malignant gliomas are the most common
primary brain tumor and have a poor clinical prognosis. 1, 3-Bis (2-chloroethyl)-1-nitrosourea (
BCNU) is an
alkylating agent that is commonly used in
glioma therapy. However,
BCNU chemotherapy often fails due to drug resistance. To gain better understanding of molecular mechanisms underlying the drug resistance of
glioma, a
BCNU-resistant variant (C6R) of C6 rat
glioma cells was selected and characterized. The established C6R cells were resistant to
BCNU-induced cell death and cell cycle arrest as confirmed by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium
bromide reduction assay and flow cytometric analysis of
DNA content. C6R cells showed an increased expression of common drug resistance-related genes such as O6-methylguanine-DNA
methyltransferase and multiple drug resistance 1. In contrast, C6R cells showed a decreased expression of
glial fibrillary acidic protein, therefore, displaying shorter cellular processes compared with parental C6 cells. More importantly, in conjunction with the morphological changes, the expression of
lipocalin-2 (lcn2), a 25-kDa secreted proapoptotic
protein, was markedly reduced in the
BCNU-resistant C6R cells. However, there was no significant change in the expression of lcn2 receptors. Addition of recombinant LCN2
protein or introduction of lcn2
cDNA significantly increased the sensitivity of C6 cells and human
glioma cells to
BCNU or other anticancer drugs, while knockdown of lcn2 expression by antisense
cDNA transfection decreased the sensitivity. When lcn2 was re-expressed in C6R cells, the
BCNU sensitivity was restored. Lcn2 enhanced
BCNU-induced Akt dephosphorylation providing a molecular basis of apoptosis sensitization. These results suggest that LCN2
protein may be involved in
glioma drug resistance and may provide a new approach to sensitizing
glioblastoma to
chemotherapy.