The effect of cycling hypoxia on MCF-7 cancer stem cells and the impact of their microenvironment on angiogenesis using human umbilical vein endothelial cells (HUVECs) as a model

Fuad M Alhawarat; Hana M Hammad; Majd S Hijjawi; Ahmad S Sharab; Duaa A Abuarqoub; Mohammad A Al Shhab; Malek A Zihlif

doi:10.7717/peerj.5990

The effect of cycling hypoxia on MCF-7 cancer stem cells and the impact of their microenvironment on angiogenesis using human umbilical vein endothelial cells (HUVECs) as a model

PeerJ. 2019 Jan 8:7:e5990. doi: 10.7717/peerj.5990. eCollection 2019.

Authors

Fuad M Alhawarat¹, Hana M Hammad¹, Majd S Hijjawi², Ahmad S Sharab², Duaa A Abuarqoub¹, Mohammad A Al Shhab², Malek A Zihlif²

Affiliations

¹ Department of Biological Sciences, School of Science, The University of Jordan, Amman, Jordan.
² Department of Pharmacology, School of Medicine, The University of Jordan, Amman, Jordan.

Abstract

Background: Breast cancer is the most common type of cancer among females. Hypoxia mediates cancer hallmarks and results from reduced oxygen level due to irregularities in tumor vascularization or when the tumor size prevents oxygen diffusion and triggers angiogenesis to compensate for low oxygen. Cancer stem cells (CSCs) are a rare subpopulation, able to self-renew and to give rise to tumor-initiating cells. It is proposed that CSCs' secretions help to recruit endothelial cells via angiogenic factors to establish tumor vascularization. In the tumor microenvironment, the effect of hypoxia on CSCs and the impact of their secretions on triggering angiogenesis and tumor vascularization remain questionable. In this study, three-dimensional (3D) CSCs derived from MCF-7 were directly exposed to repetitive long-term cycles of hypoxia to assess its effect on CSCs and then to evaluate the role of the hypoxic CSCs' (CSCs^HYP) secretions in angiogenesis using (HUVECs) as a model for tumor neovascularization response.

Methods: CSCs derived from MCF-7 cell-line were expanded under repetitive, strictly optimized, long-term/continuous and intermittent hypoxic shots for almost four months to assess hypoxic effect on CSCs, sorted based on CD44⁺/CD24^- biomarkers. Hypoxic phenotype of CSCs^HYP was evaluated by assessing the acquired chemoresistance using MTT assay and elevated stemness properties were assessed by flow cytometry. To evaluate the effect of the secretions from CSCs^HYP on angiogenesis, HUVECs were exposed to CSCs^HYP conditioned-medium (CdM)-in which CSCs had been previously grown-to mimic the tumor microenvironment and to assess the effect of the secretions from CSCs^HYP on the HUVECs' capability of tube formation, migration and wound healing. Additionally, co-culture of CSCs^HYP with HUVECs was performed.

Results: CSCs^HYP acquired higher chemoresistance, increased stemness properties and obtained greater propagation, migration, and wound healing capacities, when compared to CSCs in normoxic condition (CSCs^NOR). HUVECs' tube formation and migration abilities were mediated by hypoxic (CSCs) conditioned media (CdM).

Discussion: This study demonstrates that chemoresistant and migrational properties of CSCs are enhanced under hypoxia to a certain extent. The microenvironment of CSCs^HYP contributes to tumor angiogenesis and migration. Hypoxia is a key player in tumor angiogenesis mediated by CSCs.

Keywords: Angiogenesis; Breast Cancer; CSCs microenvironment; Cancer Stem Cell; Chemoresistance; Hypoxia; Mammosphere.

Grants and funding

This work was supported by the Deanship of Scientific Research, University of Jordan, Amman Jordan. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.