Table 1.
Overview of the main technologies used for enrichment and detection of CTCs in SCLC.
| Technology [Refs] |
CTC Enrichment | CTC Detection and Characterization |
% of CTC Detection § | Comments |
|---|---|---|---|---|
| Protein marker-based devices | ||||
| CellSearch System [12,22] | EpCAM antibodies-coated ferromagnetic beads | IF for CK8, 18, 19, DAPI and CD45 | ≥85% | FDA-approved semi-automated system. Do not detect EpCAM-negative CTCs. Do not recover viable cells. |
| CellCollector [23] | Functionalized medical wire associated with EpCAM antibodies | IF for EpCAM, CK and DAPI | Not applicable | CE-approved as medical device for in vivo CTC isolation. Capacity to process large volumes of blood with a high CTC detection rate. |
| RosetteSep System [24,25] | Depletion of leukocytes and erythrocytes by specific antibodies followed by density gradient centrifugation | ICC | 46.9% | Fast and easy-to-use. Collection of live cells with high purity for many applications (cell cultures, DNA/RNA extraction, implantation in mice). |
| Physical properties-based devices | ||||
| ISET [26,27] | Size-based filtration for isolation of CTCs | IF; FISH | 95% | Isolation of clusters and viable cells of epithelial and non-epithelial origin. Low recovery and purity. |
| ClearCell FX [28,29] | Microfluidic technology for CTC enrichment based on drag and size-dependent lift forces | IF; FISH | 85% | Capacity to capture viable and intact CTCs for in vivo and in vitro experiments and for NGS analysis. Small CTCs may escape detection. |
| CTC-iChip [30,31] | Microfluidic platform for size-based isolation in combination with EpCAM-based positive selection or CD45 negative depletion | IF; RT-PCR for tumor associated transcripts |
>77% | Detection of both epithelial and non-epithelial CTCs. Capture and in vitro culture of viable CTCs for functional studies. |
| Parsortix [32] | Microfluidic platform for cell size and deformability-based separation | IF for CK, DAPI and CD45 | 78% | CE-marked for use as in vitro diagnostic device. Collection of viable CTCs for molecular and functional analysis. |
| VTX-1 Liquid Biopsy System [33,34] | Microfluidic separation of CTCs based on cell size and deformability | IF; FISH, RT-PCR; NGS for tumor-associated transcripts | 69%-79.5% | High recovery and purity of intact CTCs. No red blood cell lysis required. Suitable for many applications (genomic and proteomic analyses, enumeration, IF staining). |
| DEPArray [35] | Requires a pre-enrichment step with other technologies (e.g., CellSearch or Parsortix) | IF for CK, CD45, DAPI or Hoechst staining |
99.7% | Recovery of single viable cells. |
| Other Assays | ||||
| TelomeScan [36,37] | Detection of GFP-positive CTCs following incubation with a telomerase-specific conditionally replicating adenovirus expressing the GFP gene | IF | >70% | Isolation of live CTCs, including EpCAM negative cells and cells undergoing EMT. A modified assay has been developed to reduce false-positive results, based on targeting miR-142-3p to inhibit GFP-expressing blood cells. |
§ calculated by spiking tumor cells into peripheral blood of healthy donors. Abbreviations: EpCAM: epithelial cell adhesion molecule; IF: immunofluorescence; CK: cytokeratins; DAPI: 4’,6-diamidino-2-phenylindole; ICC: immunocytochemistry; FDA: US Food and Drug Administration; CTCs: circulating tumor cells; NGS: next-generation sequencing; RT-PCR: reverse transcriptase polymerase chain reaction; FISH: fluorescence in situ hybridization; DEP: Dielectrophoresis; GFP: green fluorescent protein.