Intercellular cell adhesion molecule 1 (ICAM-1; also known as CD54) is overexpressed in bevacizumab-resistant glioblastoma. In the present study, we tested our hypothesis that highly expressed ICAM-1 mediates glioblastoma's resistance to antiangiogenic therapy. We validated ICAM-1 overexpression in tumors resistant to antiangiogenic therapy using real-time polymerase chain reaction, immunohistochemistry, and Western blotting. We also detected ICAM1 expression in most glioma stem cells (GSCs). We investigated the mechanism of ICAM-1 overexpression after bevacizumab treatment and found that ICAM-1 protein expression was markedly increased in a time-dependent manner in GSC11 and GSC17 cells under hypoxic conditions in vitro. We also found that hypoxia induced ICAM-1 overexpression through the up-regulation of phosphorylated signal transducer and activator of transcription (p-STAT3). Hypoxia-induced p-STAT3 increased the mRNA transcription of ICAM-1, which we could inhibit with the STAT3 inhibitor AZD1480. Next, we used GFP-tagged ICAM-1 shRNA lentivirus to knock down ICAM-1 in GSC11 and GSC17 glioma cell lines. Then, we injected shICAM-1 GSC11 and scramble glioma stem cells into the brains of nude mice. Mice bearing tumors from shICAM-1 GSC11 cells survived significantly longer than mice injected with control cells did. The tumor sizes was significantly decreased in mice bearing tumors from shICAM-1 cells than that in mice bearing tumors from GFP-tagged GSC11 control cells. Knocking down ICAM-1 suppressed tumor invasion in vitro and in vivo and inhibited macrophage infiltration to the tumor site in bevacizumab-treated mice. Our findings suggest that ICAM-1 is a potentially important mediator of tumor migration and invasion in bevacizumab-resistant glioblastoma. Targeting ICAM-1 may provide a new strategy for enhancing the efficacy of antiangiogenic therapy against glioblastoma and preventing the invasive phenotype of the disease.
Keywords: bevacizumab; intercellular cell adhesion molecule-1; macrophage; signal transducer and activator of transcription 3.