Exploring the Role of Hypoxia-Inducible Carbonic Anhydrase IX (CAIX) in Circulating Tumor Cells (CTCs) of Breast Cancer

Abstract

Circulating tumor cells (CTCs) in the peripheral blood are believed to be the source of metastasis and can be used as a liquid biopsy to monitor cancer progression and therapeutic response. However, it has been challenging to accurately detect CTCs because of their low frequency and the heterogeneity of the population. In this study, we have developed an in vitro model of CTCs by using non-adherent suspension culture. We used this model to study a group of breast cancer cell lines with distinct molecular subtypes (TNBC, HER2+, and ER+/PR+). We found that, when these breast cancer cell lines lost their attachment to the extracellular matrix, they accumulated a subtype of cancer stem cells (CSC) that expressed the surface markers of stem cells (e.g., CD44+CD24−). These stem-like CTCs also showed high expressions of hypoxia-inducible gene products, particularly the hypoxia-inducible carbonic anhydrase IX (CAIX). Inhibition of CAIX activity was found to reduce CAIX expression and stem cell phenotypes in the targeted CTCs. Further studies are needed, using CTC samples from breast cancer patients, to determine the role of CAIX in CTC survival, CSC transition, and metastasis. CAIX may be a useful surface marker for the detection of CSCs in the blood, and a potential target for treating metastatic breast cancers.

Molecular, Cellular, and Technical Aspects of Breast Cancer Cell Lines as a Foundational Tool in Cancer Research

“…The environment within which all these breast cancer cell lines must remain to grow is a laboratory-validated incubator at 37 • C. While a 5-10% CO 2 and air mixture is used in association with most available culture media, Leibovitz's L-15 medium (used for the UACC-812 cell line) is detrimental to cell cultivation in a CO 2 and air mixture environment [32]. Hs 578T RPMI/DMEM 10% FBS, 0.01 mg/mL human insulin [7,111] 1 Foundational media must be used for each breast cancer cell line: EMEM (Eagle's Minimum Essential Medium), L-15 (Leibovitz's L-15 Medium), RPMI (Roswell Park Memorial Institute-1640 medium), DMEM (Dulbecco's Modified Eagle Medium), and Ham's F12 (Ham's F-12 (Kaighn's) Medium). CO2 and air mixture are detrimental to UACC-812 cells when using an L-15 medium for cultivation.…”