Tumor cycling hypoxia induces chemoresistance in glioblastoma multiforme by upregulating the expression and function of ABCB1

Abstract

Tumor cycling hypoxia is now a well-recognized phenomenon in animal and human solid tumors. However, how tumor cycling hypoxia impacts chemotherapy is unclear. In the present study, we explored the impact and the mechanism of cycling hypoxia on tumor microenvironment-mediated chemoresistance. Hoechst 33342 staining and hypoxia-inducible factor-1 (HIF-1) activation labeling together with immunofluorescence imaging and fluorescence-activated cell sorting were used to isolate hypoxic tumor subpopulations from human glioblastoma xenografts. ABCB1 expression, P-glycoprotein function, and chemosensitivity in tumor cells derived from human glioblastoma xenografts or in vitro cycling hypoxic stress-treated glioblastoma cells were determined using Western blot analysis, drug accumulation and efflux assays, and MTT assay, respectively. ABCB1 expression and P-glycoprotein function were upregulated under cycling hypoxia in glioblastoma cells concomitant with decreased responses to doxorubicin and BCNU. However, ABCB1 knockdown inhibited these effects. Moreover, immunofluorescence imaging and flow cytometric analysis for ABCB1, HIF-1 activation, and Hoechst 3342 in glioblastoma revealed highly localized ABCB1 expression predominantly in potentially cycling hypoxic areas with HIF-1 activation and blood perfusion in the solid tumor microenvironment. The cycling hypoxic tumor cells derived from glioblastoma xenografts exhibited higher ABCB1 expression, P-glycoprotein function, and chemoresistance, compared with chronic hypoxic and normoxic cells. Tumor-bearing mice that received YC-1, an HIF-1α inhibitor, exhibited suppressed tumor microenvironment-induced ABCB1 induction and enhanced survival rate in BCNU chemotherapy. Cycling hypoxia plays a vital role in tumor microenvironment-mediated chemoresistance through the HIF-1-dependent induction of ABCB1. HIF-1 blockade before and concurrent with chemotherapy could suppress cycling hypoxia-induced chemoresistance.

Hypoxia Induced Multidrug Resistance of Laryngeal Cancer Cells via Hypoxia-inducible Factor-1α

“…The underlying mechanisms of HIF-1α in suppression of apoptosis in laryngeal cancer cells induced by chemotherapeutic drugs remains to be further determined. Besides, it has already been confirmed that the enhancement of drug transport function is another important mechanism of MDR acquired by hypoxia in several kinds of tumor cells (Thews et al, 2011;Chou et al, 2012). The present study demonstrated that hypoxia carried out an increased function of transporting a variety of chemotherapeutic drugs such as 5-FU, cisplatin, adriamycin, paclitaxel and gemcitabine, leading to decreased intracellular drug concentration and reduced cytotoxicity.…”

miR-218 opposes a critical RTK-HIF pathway in mesenchymal glioblastoma

“…These studies indicate that miR-218 repression results in enhanced RTK activity in GBM, contributing to tumor cell survival under challenging microenvironmental conditions, including chemotherapeutic stress and severe hypoxia. Tumor hypoxia has been linked to chemoresistance, and recent studies demonstrate that low O 2 concentrations maintain tumor stem cells in an undifferentiated state (34,35). HIFs (and HIF2α in particular) promote GSC self-renewal, proliferation, and survival (36).…”

The Role of Hypoxia-Inducible Factors in Cancer Resistance

“…They also used cultured human colon carcinoma cells (HCT-116, HT-29, LoVo, and SW480), and observed that HIF-1α expression was significantly associated with MDR1/P-gp expression in human colon carcinoma cells as well [65]. In addition, the expression of the multidrug resistance-associated protein 1 (MRP1), another ABC transporter, is also induced by hypoxia, and have been reported in the majority of brain tumors, including glioblastomas [66].…”