Cryopreservation of Circulating Tumor Cells for Enumeration and Characterization

Microfluidic Isolation of Disseminated Tumor Cells from the Bone Marrow of Breast Cancer Patients

Disseminated tumor cells (DTCs) in the bone marrow (BM) of breast cancer (BC) patients are putative precursors of metastatic disease, and their presence is associated with an adverse clinical outcome. To achieve the personalization of therapy on a clinical routine level, the characterization of DTCs and in vitro drug testing on DTCs are of great interest. Therefore, biobanking methods, as well as novel approaches to DTC isolation, need to be developed. In this study, we established a protocol for the biobanking of BM samples and evaluated a microfluidic-based separation system (Parsortix®) for the enrichment of cryopreserved DTCs. We were able to successfully isolate viable DTCs after the prior cryopreservation of BM samples. We calculated a significant increase of up to 90-fold in harvested DTCs with the proposed method compared to the current standard techniques, opening up new analysis possibilities for DTCs. Our advanced method further presents options for 3D DTC cultures, enabling the individualized testing of targeted therapies for BC patients. In conclusion, we present a novel approach for DTC enrichment, with possibilities for future clinical implications.

Technical Challenges for CTC Implementation in Breast Cancer

Breast cancer is the most common neoplasm in women worldwide. Tissue biopsy, currently the gold standard to obtain tumor molecular information, is invasive and might be affected by tumor heterogeneity rendering it incapable to portray the complete dynamic picture by the absence of specific genetic changes during the evolution of the disease. In contrast, liquid biopsy can provide unique opportunities for real-time monitoring of disease progression, treatment response and for studying tumor heterogeneity combining the information of DNA that tumors spread in the blood (circulating tumor DNA) with CTCs analysis. In this review, we analyze the technical and biological challenges for isolation and characterization of circulating tumor cells from breast cancer patients. Circulating tumor cell (CTC) enumeration value is included in numerous clinical studies due to the prognostic's role of these cells. Despite this, there are so many questions pending to answer. How to manage lymphocytes background, how to distinguish the CTCs subtypes or how to work with frozen samples, are some of the issues that will discuss in this review. Based on our experience, we try to address these issues and other technical limitations that should be solved to optimize the standardization of protocols, sample extraction procedures, circulating-tumor material isolation (CTCs vs. ctDNA) and the very diverse methodologies employed, aiming to consolidate the use of CTCs in the clinic. Furthermore, we think that new approaches focusing on isolation CTCs in other body fluids such as cerebrospinal or ascitic fluid are necessary to increase the opportunities of circulating tumor cells in the practice clinic as well as to study the promising role of CTC clusters and their prognostic value in metastatic breast cancer.

Feasibility of single-cell analysis of model cancer and foetal cells in blood after isolation by cell picking

The objective of the present feasibility study was to transfer single cell line cells to either microscopy slides for downstream immune characterization or to polymerase chain reaction tubes for downstream DNA quantitation. Tumour cell lines, SKBR3 and MCF7 and trophoblast cell line JEG-3 were spiked in healthy donor blood. The CytoTrack system was used to scan the spiked blood samples to identify target cells. Individual target cells were identified, picked by use of a CytoPicker and deposited to either a microscopic slide or a polymerase chain reaction tube (PCR). Single tumour cells on microscopic slides were further immunostained with human epidermal growth factor receptor 2 (Her2) and epithelial cell adhesion molecule (EpCAM). From the picked cells in polymerase chain reaction tubes, DNA was amplified, quantified and used for Short Tandem Repeat genotyping. Depositing rare cells to microscopy slides was laborious with only five cells per hour. In this study with a trained operator, the picked cells had an 80.5% recovery rate. Depositing single trophoblast cells in PCR tubes was a faster process with 10 cells in 5 min. Immunostaining of isolated cells by both Her2 and EpCAM was possible but showed varying staining intensity. Presence of trophoblasts and contaminating white blood cells in PCR tubes after cell picking was confirmed based on DNA yield and mixed Short Tandem Repeat profiles in five out of eight samples. Using the CytoPicker tool, single tumour and trophoblast cells were successfully isolated and moved from blood samples, allowing subsequent immunostaining or Short Tandem Repeat genotyping.

Cryopreservation for delayed circulating tumor cell isolation is a valid strategy for prognostic association of circulating tumor cells in gastroesophageal cancer

AIM

To demonstrate the feasibility of cryopreservation of peripheral blood mononuclear cells (PBMCs) for prognostic circulating tumor cell (CTC) detection in gastroesophageal cancer.

METHODS

Using 7.5 mL blood samples collected in EDTA tubes from patients with gastroesopheagal adenocarcinoma, CTCs were isolated by epithelial cell adhesion molecule based immunomagnetic capture using the IsoFlux platform. Paired specimens taken during the same blood draw (n = 15) were used to compare number of CTCs isolated from fresh and cryopreserved PBMCs. Blood samples were processed within 24 h to recover the PBMC fraction, with PBMCs used for fresh analysis immediately processed for CTC isolation. Cryopreservation of PBMCs lasted from 2 wk to 25.2 mo (median 14.6 mo). CTCs isolated from pre-treatment cryopreserved PBMCs (n = 43) were examined for associations with clinicopathological variables and survival outcomes.

RESULTS

While there was a significant trend to a decrease in CTC numbers associated with cryopreserved specimens (mean number of CTCs 34.4 vs 51.5, P = 0.04), this was predominately in samples with a total CTC count of > 50, with low CTC count samples less affected (P = 0.06). There was no significant association between the duration of cryopreservation and number of CTCs. In cryopreserved PBMCs from patient samples prior to treatment, a high CTC count (> 17) was associated with poorer overall survival (OS) (n = 43, HR = 4.4, 95%CI: 1.7-11.7, P = 0.0013). In multivariate analysis, after controlling for sex, age, stage, ECOG performance status, and primary tumor location, a high CTC count remained significantly associated with a poorer OS (HR = 3.7, 95%CI: 1.2-12.4, P = 0.03).

CONCLUSION

PBMC cryopreservation for delayed CTC isolation is a valid strategy to assist with sample collection, transporting and processing.