Adaptation of Semiautomated Circulating Tumor Cell (CTC) Assays for Clinical and Preclinical Research Applications

Summary

Circulating tumor cells (CTCs) are prognostic in several metastatic cancers. This manuscript describes the gold standard CellSearch system (CSS) CTC enumeration platform and highlights common misclassification errors. In addition, two adapted protocols are described for user-defined marker characterization of CTCs and CTC enumeration in preclinical mouse models of metastasis using this technology.

Abstract

The majority of cancer-related deaths occur subsequent to the development of metastatic disease. This highly lethal disease stage is associated with the presence of circulating tumor cells (CTCs). These rare cells have been demonstrated to be of clinical significance in metastatic breast, prostate, and colorectal cancers. The current gold standard in clinical CTC detection and enumeration is the FDA-cleared CellSearch system (CSS). This manuscript outlines the standard protocol utilized by this platform as well as two additional adapted protocols that describe the detailed process of user-defined marker optimization for protein characterization of patient CTCs and a comparable protocol for CTC capture in very low volumes of blood, using standard CSS reagents, for studying in vivo preclinical mouse models of metastasis. In addition, differences in CTC quality between healthy donor blood spiked with cells from tissue culture versus patient blood samples are highlighted. Finally, several commonly discrepant items that can lead to CTC misclassification errors are outlined. Taken together, these protocols will provide a useful resource for users of this platform interested in preclinical and clinical research pertaining to metastasis and CTCs.

Introduction

In 2013 it is estimated that 580,350 individuals will die from cancer and that 1,660,290 new cases of this disease will be diagnosed in the United States alone¹. The majority of these deaths occur subsequent to the development of metastatic disease². The current lack of effective therapies in treating metastases and a limited understanding of the metastatic cascade makes this stage of disease highly lethal. The presence of circulating tumor cells (CTCs) within the bloodstream have been demonstrated to correlate with metastatic disease³. These cells are extremely rare and their detection is indicative of overall survival in metastatic b....

Protocol

All human studies described in this manuscript were carried out under protocols approved by Western University's Human Research Ethics Board. All Animal studies were conducted in accordance with the recommendations of the Canadian Council on Animal Care, under protocols approved by the Western University Animal Use Subcommittee.

1. Standard CTC Enumeration from Patient Blood Samples Using the CSS

1. Human Blood Sample Collection and Preparation for Processing on the Preparation Instrument

1. Using standard aseptic phlebotomy techniques, draw a minimum of 8.0 ml of human blood into a 10 ml CellSave tube ....

Results

Standard CTC Enumeration Assay

The sensitivity and specificity of the CSS has been well documented in the literature. However, to validate equivalent CTC recovery, spiked (1,000 LNCaP human prostate cancer cells) and unspiked human blood samples from healthy volunteer donors were processed on the CSS using the standard CSSCTC protocol. As expected, unspiked samples were free of CTCs, 0.00±0.00%, and CTC recovery was demonstrated to be 86.9±4.71% for spiked samples (Figure 1A). CS.......

Discussion

Despite the development of many new CTC technologies since the introduction of the CSS in 2004, this technique is still the only clinically approved technology on the market today and therefore it is considered the current gold standard for CTC detection and enumeration. This manuscript has demonstrated that although the CSS has rigorous quality control standards it can be subject to interpretation bias and that CTC identification in patient samples is much different from identification in spiked samples. Six categories .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
0.5 M EDTA
Anti-human CD44-FITC	BD Pharmigen	555478
Anti-human CD44-PE	BD Pharmigen	555479
Anti-human HLA-Alexa Fluor 488	BioLegend	311415
Anti-mouse CD45-APC	eBioscience	17-0451-82
Bond Primary Antibody Diluent	Leica	AR9352
CellSave Preservative Tubes	Veridex	952820 (20 pack) 79100005 (100 pack)
CellSearch CTC Control Kit	Veridex	7900003
CellSearch CTC Kit	Veridex	7900001
CellSearch CXC Control Kit	Veridex	7900018RUO
CellSearch CXC Kit	Veridex	7900017RUO
Instrument Buffer	Veridex	7901003
Streck Cell Preservative (aka CytoChex)	Streck	213350
1 ml Syringe
10 ml Serological pipette
1,000 µl Pipette
1,000 µl Pipette tips
12 mm x 75 mm Flow tubes
200 µl Gel loading tips
200 µl Pipette
22 G Needle
5 3/4 in Disposible Pasteur pipet	VWR	14672-200
5 ml Serological pipette
Automated pipettor
Capillary Blood Collection Tube (EDTA)	BD Microtainer	365974
CellSearch Analyzer II	Veridex	9555	Includes magnests and verification cartirdges
CellSearch AutoPrep System	Veridex	9541
Centrifuge
MagCellect Magnet	R&D Systems	MAG997
Small Latex Bulb	VWR	82024-550
Vortex