Abstract
Free-floating tumor cells located in the blood of cancer patients, known as circulating tumor cells (CTCs), have become key targets for studying metastasis. However, effective strategies to study the free-floating behavior of tumor cells in vitro have been a major barrier limiting the understanding of the functional properties of CTCs. Upon extracellular-matrix (ECM) detachment, breast tumor cells form tubulin-based protrusions known as microtentacles (McTNs) that play a role in the aggregation and re-attachment of tumor cells to increase their metastatic efficiency. In this study, we have designed a strategy to spatially immobilize ECM-detached tumor cells while maintaining their free-floating character. We use polyelectrolyte multilayers deposited on microfluidic substrates to prevent tumor cell adhesion and the addition of lipid moieties to tether tumor cells to these surfaces through interactions with the cell membranes. This coating remains optically clear, allowing capture of high-resolution images and videos of McTNs on viable free-floating cells. In addition, we show that tethering allows for the real-time analysis of McTN dynamics on individual tumor cells and in response to tubulin-targeting drugs. The ability to image detached tumor cells can vastly enhance our understanding of CTCs under conditions that better recapitulate the microenvironments they encounter during metastasis.
Highlights
Cancer metastasis occurs when epithelial tumor cells travel through non-adherent microenvironments, like the bloodstream or lymphatics, to a distant organ
Since human breast tumor cells lines have not yet been tested on Polyelectrolyte multilayers (PEMs)-coated substrates, we first confirmed that poly(methacrylic acid) (PMA)/PAAm multilayers could prevent cell adhesion in two NCI breast cancer cell lines, MDA-MB-436 and MCF-7
While www.impactjournals.com/oncotarget in the circulation, tumor cells are in a non-adherent microenvironment that is unlike the conditions in a primary tumor or the metastatic site
Summary
Cancer metastasis occurs when epithelial tumor cells travel through non-adherent microenvironments, like the bloodstream or lymphatics, to a distant organ. The presence of tumor cells in the non-adherent microenvironment of the bloodstream, known as circulating tumor cells (CTCs), has been detected in numerous epithelial cancers including breast, prostate, colon, and lung [1]. Some of the techniques currently being employed to analyze CTCs include fluorescence in situ hybridization, sequencing, immunostaining, xenograft transplantation, and RNA or protein-based analysis [1, 4, 6, 7]. These methods do not allow for real-time analysis of CTCs in an environment that preserves their free-floating nature
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