Targeting the ABC transporter ABCB5 sensitizes glioblastoma to temozolomide-induced apoptosis through a cell-cycle checkpoint regulation mechanism

Abstract

Glioblastoma multiforme (GBM) is a malignant brain tumor with a poor prognosis resulting from tumor resistance to anticancer therapy and a high recurrence rate. Compelling evidence suggests that this is driven by subpopulations of cancer stem cells (CSCs) with tumor-initiating potential. ABC subfamily B member 5 (ABCB5) has been identified as a molecular marker for distinct subsets of chemoresistant tumor-initiating cell populations in diverse human malignancies. In the current study, we examined the potential role of ABCB5 in growth and chemoresistance of GBM. We found that ABCB5 is expressed in primary GBM tumors, in which its expression was significantly correlated with the CSC marker protein CD133 and with overall poor survival. Moreover, ABCB5 was also expressed by CD133-positive CSCs in the established human U-87 MG, LN-18, and LN-229 GBM cell lines. Antibody- or shRNA-mediated functional ABCB5 blockade inhibited proliferation and survival of GBM cells and sensitized them to temozolomide (TMZ)-induced apoptosis in vitro. Likewise, in in vivo human GBM xenograft experiments with immunodeficient mice, mAb treatment inhibited growth of mutant TP53, WT PTEN LN-229 tumors, and sensitized LN-229 tumors to TMZ therapy. Mechanistically, we demonstrate that ABCB5 blockade inhibits TMZ-induced G2/M arrest and augments TMZ-mediated cell death. Our results identify ABCB5 as a GBM chemoresistance marker and point to the potential utility of targeting ABCB5 to improve current GBM therapies.

Anticancer Properties of the Antipsychotic Drug Chlorpromazine and Its Synergism With Temozolomide in Restraining Human Glioblastoma Proliferation In Vitro

“…Cytofluorimetric assay with Calcein-AM, coupled with Annexin V/PI analysis, allowed us quantifying cell death and apoptosis in the same experimental setup. The data reported in Figure 6A, for anchorage-dependent GBM cells indicate that cells treated with TMZ became positive to Annexin V, thus suggesting an apoptotic cell death, as previously described (35,36). By contrast, CPZ appeared to induce toxicity via its ability to generate aberrant mitoses that cause nuclear fragmentation and cell death.…”

“…Indeed, while TMZ is known to block the DNA replication fork, thus arresting the cell cycle in the G2/M phase, [see Figure 2 and refs. (35,36)], CPZ, besides its ability to hinder GBM cells at the G2/M boundary (see Figure 2), appears capable of protecting aberrant or defective cells from apoptosis. Such a feature would drive these cells towards a mitosis with very little chances of being completed, eliciting, on the contrary, the generation of daughter cells with abnormal chromosomal makeup [see Figure 2 and ref (8)] and death by mitotic catastrophe.…”

Glioma stem cells and their roles within the hypoxic tumor microenvironment

“…The greater expression of the ABC transporters, in turn, strengthens chemoresistance 192 . Furthermore, ABCB5, which has been suggested to be a CSC marker in some tumors, is expressed in GSCs and mediated TMZ-resistance in GBM cells 194 .…”

Clinical Implications of Colorectal Cancer Stem Cells in the Age of Single-Cell Omics and Targeted Therapies

“…MDR has been attributed to the function of ATPbinding cassette (ABC) transporter family members, which are highly expressed in CSCs. 119 Among them, ABCB5 is a clinically relevant MDR mediator, 120 which is expressed at high levels on CSCs in several human malignancies, including malignant melanoma, [120][121][122][123][124] glioblastoma, 125 hepatocellular carcinoma, 126 breast cancer, 127 lung cancer, 128 oral cancer, 129 and CRC. 10,130 In melanoma, ABCB5 identifies CSCs that correlate with clinical disease progression, 122,131,132 which can be specifically targeted through ABCB5 to reverse drug resistance and abrogate tumor growth.…”