An ultrasensitive tumor enriched flow-cytometric assay for detection of isolated tumor cells in bone marrow of patients with breast cancer

A novel approach for detecting viable and tissue-specific circulating tumor cells through an adenovirus-based reporter vector

BACKGROUND

Circulating tumor cells (CTCs) hold great promise as biomarkers and are a direct source of tumor cells through a simple blood draw. However, CTCs are rare and their detection requires sensitive and specific methods to overcome the overwhelming hematocyte population. Therefore, CTC detection remains technically challenging.

METHODS

An assay was developed for detecting viable and tissue-specific CTCs using a tropism-enhanced and conditionally replicating reporter adenovirus (CTC-RV). Adenoviral replication was made prostate-specific by placing the E1A gene under the control of the probasin promoter and prostate-specific antigen enhancer (PSE-PBN). Viral tropism was expanded through capsid-displayed integrin targeting peptides. A secreted reporter, humanized Metridia Luciferase (hMLuc), was engineered for expression during the major late phase of viral replication. The assay involves red blood cell lysis, cell collection, viral infection, and subsequent quantification of reporter activity from cellular media. Assay and reporter stability, cell specificity and sensitivity were evaluated in cell dilution models in human blood.

RESULTS

A conditionally replicating prostate-selective adenovirus reporter and CTC assay system were generated. The secreted reporter, MLuc, was found to be stable for at least 3 days under assay conditions. CTC detection, modeled by cell dilution in blood, was selective for androgen receptor positive prostate cancer (PCa) cells. Serial dilution demonstrated assay linearity and sensitivity to as few as three cells. Prostate cancer cell viability declined after several hours in anticoagulated blood at ambient temperatures.

CONCLUSIONS

Conditionally replicative adenoviral vectors and secreted reporters offer a functional method to detect viable CTCs with cell specificity and high sensitivity.

Carboxybetaine methacrylate-modified nylon surface for circulating tumor cell capture

Conventional in vitro circulating tumor cell (CTC) detection methods are always limited by blood sample volume because of the requirement of a large amount of blood. The aim of this study was to overcome the limitation by designing and making an in vivo CTC capture device. In this study, we designed and prepared a kind of proper material to serve the purpose of intervention. A method employing 3-aminopropyltriethoxysilane (γ-APS) as the coupling reagent to graft carboxybetaine methacrylate (CBMA) and to immobilize an anti-epithelial cell adhesion molecular (EpCAM) antibody on Nylon was developed. The results of X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy proved the successful graft of γ-APS and CBMA to Nylon. Furthermore, the predicted improvement in the biocompatibilities of our modified Nylon was confirmed by water contact angle measurement, bovine serum albumin adhesion, platelet adhesion, plasma recalcification time determination, and cytotoxicity tests. The tumor cells adhesion experiment revealed that Nylon with the antibody immobilized on it had an affinity for EpCAM positive tumor cells higher than that of pristine Nylon. Additionally, the capture ability of the CTCs was demonstrated in a nude mouse tumor model using the interventional device made of the modified Nylon wire. The positive results suggest that CBMA-grafted and anti-EpCAM antibody-immobilized Nylon is a promising new material for in vivo CTC capture devices.

Circulating tumor cell analysis: technical and statistical considerations for application to the clinic

Solid cancers are a leading cause of death worldwide, primarily due to the failure of effective clinical detection and treatment of metastatic disease in distant sites. There is growing evidence that the presence of circulating tumor cells (CTCs) in the blood of cancer patients may be an important indicator of the potential for metastatic disease and poor prognosis. Technological advances have now facilitated the enumeration and characterization of CTCs using methods such as PCR, flow cytometry, image-based immunologic approaches, immunomagnetic techniques, and microchip technology. However, the rare nature of these cells requires that very sensitive and robust detection/enumeration methods be developed and validated in order to implement CTC analysis for widespread use in the clinic. This review will focus on the important technical and statistical considerations that must be taken into account when designing and implementing CTC assays, as well as the subsequent interpretation of these results for the purposes of clinical decision making.

Characterization of tumor cell dissemination patterns in preclinical models of cancer metastasis using flow cytometry and laser scanning cytometry

The inability to sensitively detect metastatic cells in preclinical models of cancer has created challenges for studying metastasis in experimental systems. We previously developed a flow cytometry (FCM) method for quantifying circulating tumor cells (CTCs) in mouse models of breast cancer. We have adapted this methodology for analysis of tumor dissemination to bone marrow (BM) and lymph node (LN), and for analysis of these samples by laser scanning cytometry (LSC). Our objective was to implement these methodologies for characterization of tumor cell dissemination in preclinical models of cancer metastasis. Human cancer cells were injected into mice via mammary fat pad (MFP; spontaneous metastasis), tail vein (TV; targets lung), or intracardiac (IC; targets bone) routes. At several time points postinjection (4 h to 8 weeks), mice were sacrificed and blood, LNs, and BM were collected. Samples were immunomagnetically enriched and labeled with human leukocytic antigen-fluorescein isothiocyanate and CD45-PE antibodies (FCM/LSC), and propidium iodide (FCM) prior to quantitative analysis. Following MFP injection, CTCs increased over time, as did disseminated cells to the LN. Interestingly, tumor cells also spontaneously disseminated to BM, peaking at 2 weeks postinjection. Following TV injection, CTCs were initially high but decreased rapidly by 1 week before increasing to peak at endpoint. Combined with an observed concurrent increase in disseminated cells to LN and BM, this suggests that tumor cells may shed into the circulation from lung metastases that establish following initial cell delivery. Following IC injection, CTCs increased over time, peaking at 4 weeks. Tumor cells in the BM (most prevalent site of metastasis after IC injection) remained at moderate levels until peaking at endpoint. Combined use of FCM and LSC allows sensitive quantification of disseminated tumor cells in preclinical models of metastasis. These methods will be valuable for future studies aimed at testing new therapeutics in the metastatic setting.

Detection of disseminated tumor cells in bone marrow of gastric cancer using magnetic activated cell sorting and fluorescent activated cell sorting

BACKGROUND AND AIM

Magnetic activated cell sorting (MACS) and fluorescent activated cell sorting (FACS) were employed to enrich and detect the gastric cancer cells from a cell line in a model system, and to enrich and detect disseminated tumor cells (DTCs) from bone marrow (BM) of patients with gastric cancer.

METHODS

Fifteen patients with benign gastric lesions and 35 patients with gastric cancer who received curative operations between December 2002 and June 2003 were selected. Mononuclear cells were separated from their BM. Cells from cell line OCUM-2M were seeded with 10-grade ratio into mononuclear cells from patients with benign gastric lesion. After labeling by MACS minibeads conjugated with cytokeratin (CK) 7/8 antibodies, anti-CK-fluorescein isothiocyanate (FITC), and anti-CD45-perdinin chlorophyll protein (PerCP), the samples were enriched twice using an MS+/RS+ positive separation column. The FACS analysis was conducted on these samples before and after MACS enrichment. The results were analyzed using clinopathological parameters.

RESULTS

Disseminated tumor cells were detected in the BM of 25 (71.43%) patients with gastric cancer. The frequencies of DTCs were 1.38 x 10(-8)-2.40 x 10(-5), 2.19 x 10(-7)-3.70 x 10(-5), 4.01 x 10(-6)-8.57 x 10(-5) in patients with well, moderately, and poorly differentiated carcinoma, respectively (P = 0.026). Disseminated tumor cells in BM had close correlation with tumor tumor-node-metastasis (TNM) stage (P = 0.034) and cancer-free survival (P = 0.035).

CONCLUSION

Disseminated tumor cells are very common in the BM of gastric cancer patients. Poor histological differentiation and more advanced TNM stage have more DTCs in the BM of gastric cancer patients. Patients with DTCs tend to have a poor prognosis.

Dielectric cell separation of fine needle aspirates from tumor xenografts

As an approach to isolating tumor cells from fine needle biopsy specimens, we investigated a dielectric cell preparation method using an in vivo xenographic tumor model. Cultured human MDA-MB-435 tumor cells were grown as solid tumors in nude mice and fine needle aspiration biopsies were conducted. Biopsied cells were suspended in sucrose medium and collected on slides patterned with microelectrode arrays (electrosmears) energized by electrical signals in the range 10 to 960 kHz. The unlabeled cells adhered to characteristic regions of the slides in accordance with their morphology as a result of dielectric forces. Tumor cells were trapped between 40 and 60 kHz and were separated according to whether they were mitotic, large and complex, or small. Damaged tumor cells were captured at between 60 and 120 kHz; granulocytes between 70 and 90 kHz; lymphocytes between 85 and 105 kHz; healthy erythrocytes between 140 and 180 kHz, and damaged erythrocytes above 180 kHz. Using intrinsic cell characteristics, the electrosmear presented cell subpopulations from fine needle aspiration biopsy specimens in a manner that is compatible with automated slide-based analysis systems. The approach has the potential to facilitate the analysis of the role of cell subpopulations in disease.

A comprehensivein vitroinvestigation of a portable magnetic separator device for human blood detoxification

A portable magnetic separator device is being developed for a proposed magnetically based detoxification system. In this paper, the performance of this device was evaluated via preliminary in vitro flow experiments using simple fluids and a separator unit consisting of one tube and two metal wires, each at the top and bottom of the tube. The effects of the following factors were observed: mean flow velocity U(o) (0.14-45 cm s(-1)), magnetic field strength micro(o)H(o) (0.125-0.50 T), wire size R(w) (0.125, 0.250 and 0.500 mm), wire length L(w) (2, 5 and 10 cm), wire materials (nickel, stainless steel 304 and 430) and tube size (outer radius R(o) = 0.30 mm and inner radius R(i) = 0.25 mm; R(o) = 0.50 mm and R(i) = 0.375 mm; and R(o) = 2.0 mm and R(i) = 1.0 mm). Our observations showed that the experimental results fit well with the corresponding theoretical results from the model we previously developed at a low flow velocity area (for example, U(o) < or = 20 cm s(-1)), strong external magnetic field (for example, > or = 0.30 T) and long wire length (for example, L(w) = 10 cm). The experimental results also showed that more than 90% capture efficiency is indeed achievable under moderate systemic and operational conditions. Pressure drop measurements revealed that the device could work well under human physiological and clinical conditions, and sphere buildup would not have any considerable effect on the pressure drop of the device. The breakthrough experiments demonstrated that a lower flow rate V, higher applied magnetic field micro(o)H(o) and diluted sphere suspension, i.e. lower C(o), would delay the breakthrough. All the results indicate the promise of this portable magnetic separator device to efficiently in vivo sequestrate nano-/micro-spheres from blood flow in the future magnetically based detoxification system.

Microsystems for isolation and electrophysiological analysis of breast cancer cells from blood

This paper presents the development of a microsystem for separating suspended breast cancer cells in peripheral blood and for sorting them based on their electrophysiological characteristics. A continuous paramagnetic capture mode (PMC) magnetophoretic microseparator was utilized for the isolation of suspended breast cancer cells in peripheral blood based on the native magnetic properties of blood cells without any tagging such as with magnetic probes. A micro-electrical impedance spectroscopy (mu-EIS) system was used as a downstream cell analysis tool to extract the pathological characteristics from the breast cancer cells. The system was fabricated on silicon and glass substrates utilizing microfabrication and stereolithography technologies. The experimental results of the PMC microseparator show that 94.8% of the breast cancer cells could be continuously separated out from a spiked blood sample with a 0.2 T external magnetic flux. The electrical impedances of human breast cancer cell lines of different pathological stages (MCF-7, MDA-MB-231, and MDA-MB-435) were measured using mu-EIS and compared to those of normal human breast tissue cell line MCF-10A.

Chemokine receptor CXCR4 expression in breast cancer as a potential predictive marker of isolated tumor cells in bone marrow

Interactions between the CXCR4 chemokine receptor in breast cancer cells and the ligand CXCL12/SDF-1alpha are thought to play an important role in breast cancer metastases. In this pilot study, CXCR4 expression along with other biomarkers including HER2-neu and EGFR, were measured in primary tumor samples of patients with operable breast cancer to test whether any of these biomarkers alone and in combination could indicate breast cancer with high likelihood of metastasizing to bone marrow. Cytokeratin (CK) positive cells in bone marrow were identified by flow-cytometry following enrichment with CK 7/8 antibody-coupled magnetic beads. Primary tumors (n = 18) were stained with specific antibodies for CXCR4, HER2-neu, EGFR, and PCNA using an indirect avidin-biotin horseradish peroxidase method. The majority of the patients had T2/T3 tumors (72%), or lymph node involvement (67%) as pathologic characteristics that were more indicative of high-risk breast cancer. High CXCR4 cytoplasmic expression was found in 7 of 18 patients (39%), whereas 6 of 18 patients (33%) were found to have CK positivity in bone marrow. The median number of CK(+) cells was 236 (range, 20-847) per 5 x 10(4) enriched BM cells. The presence of CK(+) cells in bone marrow was found to be associated with increased expression of CXCR4 alone or in addition to EGFR and/or HER2-neu expression (P = 0.013, P = 0.005, and P = 0.025, respectively) in primary tumors. Furthermore, three patients with high CK positivity (>236 CK(+) per 5 x 10(4) enriched bone marrow cells) in bone marrow exclusively expressed high levels of CXCR4 with EGFR/HER2-neu (P = 0.001). Our data suggest that high CXCR4 expression in breast cancer may be a potential marker in predicting isolated tumor cells in bone marrow. CXCR4 coexpression with EGFR/HER2-neu might further predict a particular subset of patients with high CK positivity in bone marrow.

Evaluation of multiparameter flow cytometry for the detection of breast cancer tumor cells in blood samples

We comparatively evaluated different cytokeratin (CK) reagents analyzed by flow cytometry (FCM) for the identification of the best combination of DNA/CK staining for detecting minimal numbers of breast cancer cells in peripheral blood (PB). In 59 primary breast cancer tumors, we comparatively analyzed the reactivity for up to 6 different anti-CK reagents using multiparameter FCM: anti-CK7, anti-CK20, anti-pan-CK, anti-CK8/CK18, anti-CK8, and anti-CK18. Afterward, dilutional experiments of Michigan Cancer Foundation (MCF)7 breast cancer cells in PB were performed, and the sensitivity of a DNA/CK18 staining was evaluated. Our results showed that anti-CK18 reagents were those providing the brightest and more sensitive staining for primary breast cancer tumor cells by FCM. Dilutional experiments of MCF cells in PB showed that the DNA/anti-CK18 double staining was highly specific for the identification of epithelial cells; its sensitivity ranged between 10(-6) and 10(-7) (detection of 1 tumor cell among 10(6) to 10(7) nucleated blood cells). Combined assessment of DNA cell contents and reactivity for CK18 by FCM is a sensitive method for the specific identification of breast cancer cells in PB.