Tumor cell capture from blood by flowing across antibody-coated surfaces

Ultrathin silicon nitride membrane with slit-shaped pores for high-performance separation of circulating tumor cells

In this study, we developed an ultrathin filtering membrane with slit-shaped pores which can achieve circulating tumor cell (CTC) separation from whole blood with high performance (high capture efficiency, high white blood cell (WBC) depletion, and high viability). The silicon nitride (Si₃N₄) filtering membrane was fabricated via the standard microfabrication technology, which can be easily scaled up to mass-production. 6 μm was determined as the optimum width of the filtering pores to better separate CTCs in whole blood, which can reach a high capture efficiency of ∼96%. Meanwhile, the filtering membrane with a high porosity of 34% demonstrated high WBC depletion (∼99.99%). Furthermore, the ultrathin (thickness: 200 nm) Si₃N₄ membrane facilitated the capture of CTCs with high viability (∼90%). Finally, the microfluidic chip was successfully applied to separate CTCs in whole blood samples from cancer patients and used for molecular examination. These results indicate that this microfluidic chip facilitates the clinical application of CTC-based liquid biopsy technology.

A Transparent Semiconducting Surface for Capturing and Releasing Single Cells from a Complex Cell Mixture

Selective isolation of individual target cells from a heterogeneous population is technically challenging; however, the ability to retrieve single cells can have high significance in various aspects of biological research. Here, we present a new photoelectrochemical surface based on a transparent electrode that is compatible with high-resolution fluorescence microscopy for isolating individual rare cells from complex biological samples. This is underpinned by two important factors: (i) careful design of the electrode by patterning discrete Au disks of micron dimension on amorphous silicon-indium tin oxide films and (ii) orthogonal surface chemistry, which modifies the patterned electrode with self-assembly layers of different functionalities, to selectively capture target cells on the Au disks and resist cell binding to the amorphous silicon surface. The co-stimulation of the surface using light from a microscope and an electric potential triggers the reductive desorption of the alkanethiol monolayer from the Au disks to release the single cells of interest from the illuminated regions only. Using circulating tumor cells as a model, we demonstrate the capture of cancer cells on an antibody-coated surface and selective release of single cancer cells with low expression of epithelial cell adhesion molecules.

Enhancing interactions between cells and hierarchical micro/nanostructured TiO2films for efficient capture of circulating tumor cells

Micro/nano hierarchical substrates with different micropillar spacings were designed and prepared for capture of tumor cells. The cell capture efficiency of hierarchical substrates with low-density micropillar arrays was similar to that of nanostructured substrate. Increasing the density of micopillars could significantly improve the capture efficiency. The maximum capture efficiency was achieved on the hierarchical substrate with micropillar spacings of 15μm, but further reducing the micropillar spacings did not increase the cell capture efficiency. It was also found that hierarchical substrates with appropriate spacing of micropillars appeared more favorable for cell attachment and spreading, and thus enhancing the cell-material interaction. These results suggested that optimizing the micropillar arrays, such as the spacing between adjacent micropillars, could give full play to the synergistic effect of hierarchical hybrid micro/nanostructures in the interaction with cells. This study may provide promising guidance to design and optimize micro/nano hierarchical structures of biointerfaces for biomedical application.

Magnetic Particles for CTC Enrichment

Simple Summary

For the enrichment of very rare cells, such as Circulating Tumor Cells (CTCs), immunomagnetic enrichment is frequently used. For this purpose, magnetic nanoparticles (MNPs) coated with specific antibodies directed against cancer cells are used. In this review, we look at the properties such a particle needs to have in order to be used successfully, and describe the different methods used in the production of such a particle as well as the methods for their separation. Additionally, an overview is given of the antibodies that could potentially be used for this purpose.

Abstract

Here, we review the characteristics and synthesis of magnetic nanoparticles (MNPs) and place these in the context of their usage in the immunomagnetic enrichment of Circulating Tumor Cells (CTCs). The importance of the different characteristics is explained, the need for a very specific enrichment is emphasized and different (commercial) magnetic separation techniques are shown. As the specificity of an MNP is in a large part dependent on the antibody coated onto the particle, different strategies in the coupling of specific antibodies as well as an overview of the available antibodies is given.

A microfluidic device for differential capture of heterogeneous rare tumor cells with epithelial and mesenchymal phenotypes

Accumulating evidence suggests that the features associated with epithelial to mesenchymal transition (EMT) in circulating tumor cells (CTCs) reflect intrinsic metastatic potential and associate with therapy resistance. Thus, profiling the EMT phenotypes of CTCs is increasingly important for cancer diagnosis and prediction of therapeutic responses. However, rapid assessment of the EMT status of a global CTC population is still a challenge due to the difficulty in enriching and phenotyping CTCs simultaneously. Here, we report a microfluidic device consisting of an enrichment section and a capture section for differential capture of rare tumor cells from blood according to their EMT phenotypes. A row of micropillars was constructed in the enrichment section to provide cross-flows for the size-dependent filtration of cells. Thus, MCF-7 and MDA-MB-231 tumor cells mimicking CTCs were first separated from white blood cells through the micropillars and continually flowed into the capture section at a reduced velocity under a differential hydrodynamic pressure. In the capture section, the heterogeneous tumor cells were then phenotypically sorted and captured in two cascaded compartments functionalized with either an anti-EpCAM antibody or a cocktail of antibodies against mesenchymal markers including Axl, PD-L1, and EGFR. Direct counting of the captured cells in each compartment resulted in the enumeration of epithelial and mesenchymal subpopulations of the tumor cells without additional labeling. Furthermore, the captured tumor cells were successfully maintained for up to six days in the device with high viability and marked proliferation for downstream analysis. Thus, this integrated microfluidic device may have great potential in phenotyping EMT status of CTCs for precision cancer therapy.

Dynamically Monitoring the Clonal Evolution of Lung Cancer Based on the Molecular Characterization of Circulating Tumor Cells Using Aptamer Cocktail-Modified Nanosubstrates

Dynamically monitoring the clonal evolution of lung cancer and performing molecular analyses on tumor cells are challenging but necessary tasks to adjust therapeutic interventions and evaluate treatment efficacy. Circulating tumor cells (CTCs), as a "liquid biopsy", may offer an auxiliary tool to identify phenotypic transformation of solid tumors at primary or metastatic sites and uncover their corresponding molecular variation. Herein, we developed an aptamer-modified PEG-PLGA-nanofiber (PPN) microfluidic system optimized for recognizing rare CTC subtypes in lung cancer patients. This unique purification system can be adopted to monitor the clonal evolution of solid tumors by following the intrinsic immunophenotypes of CTCs, while significantly enhancing capture efficiency for polyclonal-derived tumor cells, further facilitating therapeutic evaluation via dynamic CTC enumeration. Combining with downstream single-cell sequencing, the aptamer-modified-PPN microfluidic system was able to provide early insight into tumor heterogeneity and predict histologic transformation in advance, broadening its clinical applications in lung cancer patients.

Antibody-Functional Microsphere-Integrated Filter Chip with Inertial Microflow for Size-Immune-Capturing and Digital Detection of Circulating Tumor Cells

Circulating tumor cells (CTCs) in blood is the direct cause of tumor metastasis. The isolation and detection of CTCs in the whole blood is very important and of clinical value in early diagnosis, postoperative review, and personalized treatment. It is difficult to separate all types of CTCs that efficiently rely on a single path due to cancer cell heterogenicity. Here, we designed a new kind of "filter chip" for the retention of CTCs with very high efficiency by integrating the effects of cell size and specific antigens on the surface of tumor cells. The filter chip consists of a semicircle arc and arrays and can separate large-scale CTC microspheres, which combined with CTCs automatically. We synthesized interfacial zinc oxide coating with nanostructure on the surface of the microsphere to increase the specific surface area to enhance the capturing efficiency of CTCs. Microspheres, trapped in the arrays, would entrap CTCs, too. The combination of the three kinds of strategies resulted in more than 90% capture efficiency of different tumor cell lines. Furthermore, it is easy to find and isolate the circulating tumor cells from the chip as tumor cells would be fixed inside the structure of a filter chip. To avoid the high background contamination when a few CTCs are surrounded by millions of nontarget cells, a digital detection method was applied to improve the detection sensitivity. The CTCs in the whole blood were specifically labeled by the antibody-DNA conjugates and detected via the DNA of the conjugates with a signal amplification. The strategy of the antibody-functional microsphere-integrated microchip for cell sorting and detection of CTCs may find broad implications that favor the fundamental cancer biology research, the precise diagnosis, and monitoring of cancer in the clinics.

Glass Chemistry to Analyze Human Cells under Adverse Conditions

Emerging point-of-care diagnostic tests capable of analyzing whole mammalian cells often rely on the attachment of harvested cells to glass surfaces for subsequent molecular characterization. We set out to develop and optimize a kit for the diagnosis of lymphoma in low- and middle-income countries where access to advanced healthcare testing is often absent or prone to error. Here, we optimized a process for the lyophilization of neutravidin-coated glass and cocktails of antibodies relevant to lymphoma diagnosis to establish long-term stability of reagents required for point-of-care cell capture technology. Lyophilized glass slides showed no decline in their performance compared to freshly prepared neutravidin glass and preserved capture efficiency for 5 weeks under easily attainable storage conditions. We demonstrate the successful performance of the low-cost, lyophilized kit in a cell capture assay to enable true point-of-care analyses under adverse conditions. We anticipate that the strategy can be expanded to other cancer cell types or cell-derived vesicle analysis.

Heterogeneity in Circulating Tumor Cells: The Relevance of the Stem-Cell Subset

The release of circulating tumor cells (CTCs) into vasculature is an early event in the metastatic process. The analysis of CTCs in patients has recently received widespread attention because of its clinical implications, particularly for precision medicine. Accumulated evidence documents a large heterogeneity in CTCs across patients. Currently, the most accepted view is that tumor cells with an intermediate phenotype between epithelial and mesenchymal have the highest plasticity. Indeed, the existence of a meta-stable or partial epithelial–mesenchymal transition (EMT) cell state, with both epithelial and mesenchymal features, can be easily reconciled with the concept of a highly plastic stem-like state. A close connection between EMT and cancer stem cells (CSC) traits, with enhanced metastatic competence and drug resistance, has also been described. Accordingly, a subset of CTCs consisting of CSC, present a stemness profile, are able to survive chemotherapy, and generate metastases after xenotransplantation in immunodeficient mice. In the present review, we discuss the current evidence connecting CTCs, EMT, and stemness. An improved understanding of the CTC/EMT/CSC connections may uncover novel therapeutic targets, irrespective of the tumor type, since most cancers seem to harbor a pool of CSCs, and disclose important mechanisms underlying tumorigenicity.