Targeting highly expressed extracellular HSP90 in breast cancer stem cells inhibits tumor growthin vitroandin vivo

Abstract

Breast cancer stem cells (BCSC) have been identified in breast carcinoma as CD44 C /CD24 ¡/low cells, which display tumorigenic activity and have the ability to self-renew, differentiate and metastasize. Previous studies showed that extracellular HSP90 (eHSP90) participates in the invasion and metastatic processes of various cancers including breast cancer. Here, we show for the first time that eHSP90 is over-expressed in mammosphere cultures that are derived from the MDA-MB-231, MDA-MB-453 and MCF-7 breast cancer cell lines. These mammospheres are highly enriched in cells of the CD44 C /CD24 ¡/low BCSC phenotype and additionally show high expression of the BCSC markers CD49f and Sox2. Thus our results indicate that eHSP90 represents a potential novel BCSC marker. Moreover, we present evidence that eHSP90 is functionally involved in BCSC activity in vitro and in vivo. Selective neutralization of eHSP90, using the monoclonal antibody mAb 4C5, has the capacity to inhibit stem cell activity in vitro because the formation of mammosphere-derived colonies is dramatically reduced in its presence. In vivo, the treatment of mice with mAb4C5 using a prophylactic protocol, significantly inhibited the primary growth of MDA-MB-231 and mammosphere-derived tumors. More importantly, administration of this antibody in a therapeutic protocol caused a statistically significant regression of established tumors derived from MDA-MB-231 originating mammospheres. Tumor regression was even greater when mAb 4C5 was administered in combination with paclitaxel. Overall, our findings implicate eHSP90 as a potential novel BCSC biomarker. Moreover they show that eHSP90 participates in BCSC-derived primary tumor growth. Finally, we provide additional support for the possible therapeutic value of mAb4C5 in the treatment of breast cancer.Abbreviations: ALDH1, aldehyde dehydrogenase 1; BCSC, breast cancer stem cells; eHSP90, extracellular heat shock protein 90; ER, estrogen receptor; EGF, epidermal growth factor; FGF, fibroblast growth factor; MMP-2, matrix metalloproteinase 2

Anti-Breast Cancer Activities of 8-Hydroxydaidzein by Targeting Breast Cancer Stem-Like Cells

“…According to previous reports and results of our study, breast cancer cells-derived mammospheres are highly enriched with cells that have BCSC phenotype and generally show increased expression of the BCSC markers (27). In our study, we also examined the effect of 8-OHD (70 μM) on stemness markers such as Wnt1, Notch1, β-catenin, CXCR4, SOX2, and ALDH3A1 in mammosphere cell culture.…”

Molecular Chaperones in Cancer Stem Cells: Determinants of Stemness and Potential Targets for Antitumor Therapy

“…In turn, extracellular (secreted or cell surface bound) HSP90 can also play an important role in the development and manifestations of cancer cell stemness. At least, the implication of extracellular HSP90 in CSC phenotype regulation was clearly demonstrated for prostate cancer [102][103][104][105], breast cancer [106,107], and colorectal cancer [108].…”

“…Studying breast cancer-derived cell lines, Stivarou et al found that extracellular HSP90 was overexpressed in mammosphere-forming cell cultures, while the mammospheres were enriched with CSC-like CD44(+)/CD24(−/low) cells; the authors suggested that extracellular HSP90 represents a phenotypic marker of breast CSCs [106]. It was recently reported that the secretion of HSP90 by breast CSCs is required for cancer-related signaling pathways and breast tumor xenograft growth in mice [109]; inhibiting the HSP90 secretion and/or extracellular HSP90 functions was therefore suggested as a potential approach to CSC-based therapy of cancer.…”

“…Finally, HSP90 expressed on the CSC surface may be a target for immunotherapy of cancer. As HSP90 was suggested to be a specific surface marker of human breast CSCs, an anti-HSP90 monoclonal antibody 4C5 was produced, which inhibited both the cancer stemness-related activity of human breast cancer cells in vitro and the primary growth of mammosphere-derived tumors in immunodeficient mice [106]. Monoclonal antibodies with a high specificity/affinity for CSC surface-bound HSP90 may be conjugated to certain toxins or radionuclides and thus be used in vivo as vectors for the targeted delivery of cell-killing agents to CSCs.…”

Cytosolic Hsp90α and its mitochondrial isoform Trap1 are differentially required in a breast cancer model

“…eHsp90α has been proposed to be important in a number of physiological and pathophysiological processes including tumor growth [13], invasion and metastasis [7, 14], wound healing [15], and angiogenesis [16]. It has been suggested that Hsp90 secretion in normal cells only occurs under stress, but is constitutive in certain tumor cells [17], although not in all [18].…”