Is small smarter? Nanomaterial-based detection and elimination of circulating tumor cells: current knowledge and perspectives

Figures & data

Figure 1 Timeline of PubMed entries.

Notes: Search criteria included “nanotechnology” AND “CTCs”, “nano” AND “CTCs”, and “nano” AND “circulating tumor cells” to determine number of publications (columns). Timeline of World Health Organization International Clinical Trials Registry Platform entries to display the number of registered clinical trials using search criteria “circulating tumor cells” AND “nano”.

Figure 2 Workflow of patient-derived CTCs for CTC analysis, drug-resistance detection, and personalized drug-delivery systems.

Notes: Patients’ blood samples are screened and potential CTCs captured and isolated. Potential CTCs can be enumerated, determined, and stained or cultivated for further analysis. CTC culture can be used for drug-resistance detection and personalized drug development, thereby increasing patient-survival rates.

Abbreviation: CTCs, circulating tumor cells.

Figure 3 Characteristic stages of tumor-cell dissemination during metastasis.

Notes: Cells from primary tumors undergo epithelial–mesenchymal transition (EMT), leading to the loss of cell–cell adhesion and promoting local invasion into the blood vessels (intravasation). The CTCs produced are able to escape from blood vessels into distant organs of future metastasis (extravasation) after the reverse process (MET), induced by interaction with the local microenvironment.

Abbreviations: CTCs, circulating tumor cells; MET, mesenchymal-to-epithelial transition.

Table 1 Summary of key biomarkers used for CTC detection

Epithelial markers	Mesenchymal markers	Stem-cell markers	Lymphocyte, platelet, and apoptosis markers
EpCAM	N-cadherin	ALDH1	CD45 (lymphocytes)
CK8, CK18, CK19	Cell-surface vimentin	CD44	CD61 (megakaryocytes, platelets)
E-cadherin	Twist1	Gangliosides (GD2, GD3, GD1a)	M30 (apoptosis)
ZO1	Akt and PI3K	ABC proteins
ESPR1	Zeb1
HER2	Alternative splicing proteins (FGFR2IIIc, Mena, p120 catenin)
	Pls3

Abbreviation: CTC, circulating tumor cell.

Figure 4 Illustration of methods for CTC isolation by magnetic separation using magnetic nanoparticles (NPs).

Notes: (A) The CellSearch system enriches CTCs using iron NPs linked with anti-EpCAM antibodies (Abs). Labeled cells are magnetically separated, and can be evaluated by immunofluorescence staining. (B) AdnaTest allows the immunomagnetic enrichment of CTCs via epithelial and tumor-specific antigens. After separation of potential CTCs from PBMCs, labeled cells are lysed, in order to analyze CTC gene expression via multiplex PCR. (C) Process of MACS using superparamagnetic Fe NPs within a magnetized steel-wool column.

Abbreviations: CTCs, circulating tumor cells; PBMCs, peripheral blood mononuclear cells; MACS, magnetically activated cell sorting; RT, real time.

Figure 5 Microfluidic chip design of CTC chip (A) and herringbone chip (B).

Notes: Whole-blood sample is pushed through the surface of the chip, which is coated with a CTC-specific antibody, such as EpCAM. Chips differ in their architecture, containing either Ab-coated microposts (A) or herringbone-etched microchannels (B). Captured cells are stained for CK, CD45, and DAPI. Identified CTCs can be enumerated.

Abbreviations: CTC, circulating tumor cell; Ab, antibody; MNPs, magnetic nanoparticles.

Figure 6 Synergetic detection and destruction of CTCs by a “sense-and-treat” DNA nanosystem.

Notes: Reproduced with permission from Chen N, Qin S, Yang X, Wang Q, Huang J, Wang K. “Sense-and-treat” DNA nanodevice for synergetic destruction of circulating tumor cells. ACS Appl Mater Interfaces. 2016;8(40):26552–26558. Copyright © 2016 American Chemical Society.¹⁴²

Abbreviations: CTCs, circulating tumor cells; Dox, doxorubicin.

Table 2 Overview of NP-based CTC detection methods

Nanomaterial	Pros	Cons	References
MNPs/nanoclusters	Biocompatibility, magnetic separation, high sensitivity	Magnetic aggregation; dependence on binding capacity of MNPs (affinity-based)	^Citation42, ^Citation109^–^Citation112
Fe-core MNPs	High magnetic moments, superparamagnetic	Rapid oxidation → protective shells needed	^Citation57
Magnetic–optical bifunctional NPs	Simultaneous detection and isolation of various tumor-cell types, killing by X-ray-based detection possible	Affinity-based	^Citation53
Micro-NMR	Rapid, highly sensitive biomarker detection, only minimal sample purification necessary	Variation in NMR frequency depending on temperature	^Citation57
Quantum dots	Quantitative detection with high sensitivity, various fluorescence types enable capture of heterogeneous CTCs	Toxicity affects viability (no further investigations possible), intermittence under continuous excitation	^Citation21, ^Citation53
Gold NPs	Microsurgical removal/laser-controlled detection and direct ablation of CTCs, postcapture analysis	Nonbiodegradability, complicated preparation	^Citation21, ^Citation53, ^Citation113, ^Citation114
Graphene/graphene oxides	High specificity, multiplex functionalization, label-free detection, high conductivity, no toxicity, easy functionalization	Aspecific cellular internalization, hybrid sensors not reproducible yet	^Citation21, ^Citation53, ^Citation92, ^Citation115^–^Citation118
Liposomes	Biocompatibility, long blood-circulation time	Low stability	^Citation21, ^Citation119, ^Citation120
Polymeric nanomaterials	Biocompatibility and biodegradability, ease of chemical modification, drug encapsulation/conjugation, improves sensitivity/selectivity of surfaces for CTC detection	Low stability	^Citation53, ^Citation97, ^Citation121
Hybrid NPs	Recovery of viable cells, can proliferate in vitro	Different hybrid NPs for different types of CTCs necessary, all trials still in vitro	^Citation100
SWCNTs/MWCNTs	High stability, bioactivity, capable of cell capture, high sensitivity, even in whole blood	One type of aptamer binds only one specific target	^Citation122
Microfabricated filters	Label-free, unbiased	Sensitivity to size	^Citation12, ^Citation42
Microfluidic-enabled immunoseparation	High efficiency, sensitivity, throughput, automatic, further molecular analysis	Relied on microscopy imaging for CTC identification after isolation	^Citation12, ^Citation36, ^Citation42, ^Citation65, ^Citation123
Herringbone chip	Transparent device for better imaging		^Citation12, ^Citation36, ^Citation116
CTC chip	High throughput, combination of immunomagnetic sorting with micropost-based enrichment		^Citation12, ^Citation36, ^Citation116, ^Citation124
Micro–Hall detector	Rapid detection, high contrast against blood cells, detection of multiple biomarkers	Limited throughput (about 10^7 cells)	^Citation124, ^Citation125
Gilupi nanodetector	Large volume analyzed	Affinity-based, complex procedure	^Citation12, ^Citation36

Note: Data from Zhang and King.²¹

Abbreviations: MNPs, magnetic nanoparticles; CTC, circulating tumor cell; SWCNTs, single-walled carbon nanotubes; MWCNTs, multiwalled CNTs; NMR, nuclear magnetic resonance; NP, nanoparticle.

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