A facile in vitro platform to study cancer cell dormancy under hypoxic microenvironments using CoCl(2)

BACKGROUND: While hypoxia has been well-studied in various tumor microenvironments, its role in cancer cell dormancy is poorly understood, in part due to a lack of well-established in vitro and in vivo models. Hypoxic conditions under conventional hypoxia chambers are relatively unstable and cannot be maintained during characterization outside the chamber since normoxic response is quickly established. To address this challenge, we report a robust in vitro cancer dormancy model under a hypoxia-mimicking microenvironment using cobalt chloride (CoCl(2)), a hypoxia-mimetic agent, which stabilizes hypoxia inducible factor 1-alpha (HIF1α), a major regulator of hypoxia signaling. METHODS: We compared cellular responses to CoCl(2) and true hypoxia (0.1% O(2)) in different breast cancer cell lines (MCF-7 and MDA-MB-231) to investigate whether hypoxic regulation of breast cancer dormancy could be mimicked by CoCl(2). To this end, expression levels of hypoxia markers HIF1α and GLUT1 and proliferation marker Ki67, cell growth, cell cycle distribution, and protein and gene expression were evaluated under both CoCl(2) and true hypoxia. To further validate our platform, the ovarian cancer cell line OVCAR-3 was also tested. RESULTS: Our results demonstrate that CoCl(2) can mimic hypoxic regulation of cancer dormancy in MCF-7 and MDA-MB-231 breast cancer cell lines, recapitulating the differential responses of these cell lines to true hypoxia in 2D and 3D. Moreover, distinct gene expression profiles in MCF-7 and MDA-MB-231 cells under CoCl(2) treatment suggest that key cell cycle components are differentially regulated by the same hypoxic stress. In addition, the induction of dormancy in MCF-7 cells under CoCl(2) treatment is HIF1α-dependent, as evidenced by the inability of HIF1α-suppressed MCF-7 cells to exhibit dormant behavior upon CoCl(2) treatment. Furthermore, CoCl(2) also induces and stably maintains dormancy in OVCAR-3 ovarian cancer cells. CONCLUSIONS: These results demonstrate that this CoCl(2)-based model could provide a widely applicable in vitro platform for understanding induction of cancer cell dormancy under hypoxic stress. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13036-018-0106-7) contains supplementary material, which is available to authorized users.