The analysis of circulating tumor cells (CTCs) allows a noninvasive method of “real-time liquid biopsy” from the blood samples of cancer patients for the diagnosis of early-stage cancer, prognosis, and monitoring therapeutic response. In this study, we develop a simple, inexpensive, and reliable method that utilizes a small molecule peptide, the asparagine-glycine-arginine (NGR), as a capture probe for the selective enrichment and isolation of circulating tumor cells (CTCs). The multiscale TiO₂ nanofibers are obtained by electrospinning and calcination. Bovine serum albumin (BSA) is decorated onto TiO₂ nanofiber surfaces to inhibit non-target cell adhesion, while NGR peptides are conjugated onto the TiO₂-BSA surface through the glutaraldehyde (GA) to specifically capture the target cells. The TiO₂-BSA-NGR substrate exhibits a high capture sensitivity and efficiency from the mimical blood samples with PC-3 cancer cells as low as 10 cells/mL. The TiO₂ nanofiber substrate can be a promising strategy for the capture and enumeration of CTCs in cancer progression monitoring. Graphic Abstract

The isolation of specific and sensitive circulating tumor cells (CTCs) is significant for applying them in cancer diagnosis and monitoring. In this work, dual aptamer-modified poly(lactic-co-glycolic acid) (PLGA) nanofiber-based microfluidic devices were fabricated to achieve the highly efficient capture and specific release of epithelial and mesenchymal CTCs of ovarian cancer. Dual aptamer targeting epithelial cell adhesion molecules (EpCAM) and N-cadherin proteins to improve the capture sensitivity, bovine serum albumin (BSA) to guarantee the capture purity and the nanofibers to increase the capture efficiency via synchronously and effectively capturing the epithelial and mesenchymal CTCs with good capture specificity and sensitivity from blood samples were used. We used the target cells including the ovarian cancer A2780 cells (N-cadherin-high, EpCAM-low) and OVCAR-3 cells (EpCAM-high, N-cadherin-low) to test the devices, which exhibited good capture efficiency (91% for A2780 cells, 89% for OVCAR-3 cells), release efficiency (95% for A2780 cells, 88% for OVCAR-3 cells), and sensitivity for rare cells (92% for A2780 cells, 88% for OVCAR-3 cells). Finally, the clinical blood samples of ovarian cancer patients were detected by the PLGA nanofiber-based microfluidic device, and 1 to 13 CTCs were successfully confirmed to be captured with the help of immunofluorescence staining identification. The results exhibited that the dual aptamer-modified PLGA nanofiber-based microfluidic device used as a tool for CTC capture has the potential for clinical application to guide the diagnosis, treatment, and prognosis of ovarian cancer patients.

Circulating tumor cells (CTCs) acquire mesenchymal markers (e.g., N-cadherin) and lose epithelial markers (e.g., epithelial cell adhesion molecule, EpCAM) during the epithelial-mesenchymal transition (EMT) and are therefore ideal biomarkers of tumor metastasis. However, it is still a challenge to efficiently capture and detect circulating tumor cells with different phenotypes simultaneously. In this work, to obtain aptamers targeting N-cadherin in the native conformation on live cells, we established stable N-cadherin overexpressing cells (N-cadherin cells) and used these cells to identify a panel of N-cadherin-specific aptamers through the cell-SELEX approach. Two aptamer candidates obtained after 12 rounds of selection showed a low equilibrium dissociation constant in the nanomolar range, indicating high binding affinity. The truncated aptamer candidate NC3S showed the highest binding affinity to N-cadherin cells with a low K_d value of 20.08 nM. The SYL3C aptamer was reported to target cancer cell surface biomarker EpCAM. Then, we synthesized two kinds of aptamer-modified magnetic nanoparticles (SYL3C-MNPs and NC3S-MNPs). Both SYL3C and NC3S aptamers possess excellent capture specificity and efficiency for the target cells. The aptamer–MNP cocktail exhibits a considerable capture efficiency and sensitivity for rare cancer cells of epithelial and mesenchymal phenotypes. Furthermore, no CTCs were found in blood samples from healthy donors, while CTCs were successfully isolated by using the aptamer–MNP cocktail for 15 out of 16 samples collected from patients. In summary, the two kinds of aptamer-modified MNPs could be utilized as a promising tool for capturing CTCs from clinical samples.

This paper summarizes various aptamer-functionalized nanostructured interfaces for the detection and release of circulating tumor cells.