Simon P. Duffy

Morphological Differences between Circulating Tumor Cells from Prostate Cancer Patients and Cultured Prostate Cancer Cells

Circulating tumor cell (CTC) enumeration promises to be an important predictor of clinical outcome for a range of cancers. Established CTC enumeration methods primarily rely on affinity capture of cell surface antigens, and have been criticized for underestimation of CTC numbers due to antigenic bias. Emerging CTC capture strategies typically distinguish these cells based on their assumed biomechanical characteristics, which are often validated using cultured cancer cells. In this study, we developed a software tool to investigate the morphological properties of CTCs from patients with castrate resistant prostate cancer and cultured prostate cancer cells in order to establish whether the latter is an appropriate model for the former. We isolated both CTCs and cultured cancer cells from whole blood using the CellSearch® system and examined various cytomorphological characteristics. In contrast with cultured cancer cells, CTCs enriched by CellSearch® system were found to have significantly smaller size, larger nuclear-cytoplasmic ratio, and more elongated shape. These CTCs were also found to exhibit significantly more variability than cultured cancer cells in nuclear-cytoplasmic ratio and shape profile.

Continuous Flow Deformability‐Based Separation of Circulating Tumor Cells Using Microfluidic Ratchets

Circulating tumor cells (CTCs) offer tremendous potential for the detection and characterization of cancer. A key challenge for their isolation and subsequent analysis is the extreme rarity of these cells in circulation. Here, a novel label-free method is described to enrich viable CTCs directly from whole blood based on their distinct deformability relative to hematological cells. This mechanism leverages the deformation of single cells through tapered micrometer scale constrictions using oscillatory flow in order to generate a ratcheting effect that produces distinct flow paths for CTCs, leukocytes, and erythrocytes. A label-free separation of circulating tumor cells from whole blood is demonstrated, where target cells can be separated from background cells based on deformability despite their nearly identical size. In doping experiments, this microfluidic device is able to capture >90% of cancer cells from unprocessed whole blood to achieve 10(4) -fold enrichment of target cells relative to leukocytes. In patients with metastatic castration-resistant prostate cancer, where CTCs are not significantly larger than leukocytes, CTCs can be captured based on deformability at 25× greater yield than with the conventional CellSearch system. Finally, the CTCs separated using this approach are collected in suspension and are available for downstream molecular characterization.

Microfluidic analysis of red blood cell deformability.

A common indicator of rheological dysfunction is a measurable decrease in the deformability of red blood cells (RBCs). Decreased RBC deformability is associated with cellular stress or pathology and can impede the transit of these cells through the microvasculature, where RBCs play a central role in the oxygenation of tissues. Therefore, RBC deformability has been recognized as a sensitive biomarker for rheological disease. In the current study, we present a strategy to measure RBC cortical tension as an indicator of RBC deformability based on the critical pressure required for RBC transit through microscale funnel constrictions. By modeling RBCs as a Newtonian liquid drop, we were able to discriminate cells fixed with glutaraldehyde concentrations that vary as little as 0.001%. When RBCs were sampled from healthy donors on different days, the RBC cortical tension was found to be highly reproducible. Inter-individual variability was similarly reproducible, showing only slightly greater variability, which might reflect biological differences between normal individuals. Both the sensitivity and reproducibility of cortical tension, as an indicator of RBC deformability, make it well-suited for biological and clinical analysis of RBC microrheology.

Microfluidic deformability analysis of the red cell storage lesion

A key challenge in transfusion medicine research and clinical hematology is to develop a simple and non-destructive method to measure the quality of each blood unit prior to use. RBC deformability has long been proposed as an indicator of blood quality. We measured RBC deformability using the pressure required for single cells to transit through a micrometer scale constriction to examine longitudinal changes in RBC deformability, as well as the variability in blood quality and storage capacity across donors. We used a microfluidic device to monitor deformability changes in RBCs stored in plastic tubes and in blood bags over 14 and 56 days respectively. We found consistent storage based degradation of RBC deformability with statistically significant variability in both the initial RBC deformability and storage capacity among donors. Furthermore, all samples exhibited a transient recovery phenomenon. Deformability profiling of stored RBCs using transiting pressure showed significant donor variability in initial quality and storage capacity. This measurement approach shows promise as a rapid method to individually assess the quality of stored RBC units.

Microfluidic enrichment of circulating tumor cells in patients with clinically localized prostate cancer

BACKGROUND Circulating tumor cells (CTC) have become an important tool in the monitoring of patients with advanced prostate cancer (PC). The role of CTC in localized disease has been addressed by only few studies. However, results of CTC analyses are strongly dependent on the platform used for CTC enrichment and detection. In the present study, a microfluidic platform allowing for antigen-independent enrichment of CTC was investigated for its ability to detect CTC in patients with clinically localized PC. PATIENTS AND METHODS Blood (2ml) was collected preoperatively from 50 consecutive patients undergoing radical prostatectomy for clinically localized PC. CTC were enriched using a microfluidic ratchet mechanism allowing separation of CTC from white blood cells based on differences in size and deformability. Enriched cells were stained for immunofluorescence with antibodies targeting pancytokeratin, epithelial cell adhesion molecule, and CD45. In 21 patients, we performed staining for the androgen receptor. CTC counts were correlated with clinical and pathological parameters using the Wilcoxon-Mann-Whitney test for continuous parameters and Chi-square test for categorical parameters. RESULTS CTC were detected in 25 (50%) patients. The median number of CTC in CTC-positive patients was 9 CTC/2ml (range: 1-417). Pancytokeratin positive CTC showed expression of androgen the receptor. We observed no correlation between CTC counts and prostate-specific antigen concentration, tumor stage, lymph node stage, or Gleason grade. CONCLUSION In a representative cohort of patients with clinically localized PC, CTC can be detected in a considerable proportion of patients when using a new microfluidic ratchet mechanism. This encourages further studies assessing the prognostic effect of antigen-independent enriched CTC in patients with PC.

Deformability based Cell Sorting using Microfluidic Ratchets Enabling Phenotypic Separation of Leukocytes Directly from Whole Blood

The separation of leukocytes from whole blood is a prerequisite for many biological assays. Traditional methods require significant sample volumes and are often undesirable because they expose leukocytes to harsh physical or chemical treatment. Existing microfluidic approaches can work with smaller volumes, but lack selectivity. In particular, the selectivity of microfluidic systems based on microfiltration is limited by fouling due to clogging. Here, we developed a method to separate leukocytes from whole blood using the microfluidic ratchet mechanism, which filters the blood sample using a matrix of micrometer-scale tapered constrictions. Deforming single cells through such constrictions requires directionally asymmetrical forces, which enables oscillatory flow to create a ratcheting transport that depends on cell size and deformability. Simultaneously, oscillatory flow continuously agitates the cells to limit the contact time with the filter microstructure to prevent adsorption and clogging. We show this device is capable of isolating leukocytes from whole blood with 100% purity (i.e. no contaminant erythrocytes) and <2% leukocytes loss. We further demonstrate the potential to phenotypically sort leukocytes to enrich for granulocytes and lymphocytes subpopulations. Together, this process provides a sensitive method to isolate and sort leukocytes directly from whole blood based on their biophysical properties.

Reduced deformability of parasitized red blood cells as a biomarker for anti-malarial drug efficacy

BackgroundMalaria remains a challenging and fatal infectious disease in developing nations and the urgency for the development of new drugs is even greater due to the rapid spread of anti-malarial drug resistance. While numerous parasite genetic, protein and metabolite biomarkers have been proposed for testing emerging anti-malarial compounds, they do not universally correspond with drug efficacy. The biophysical character of parasitized cells is a compelling alternative to these conventional biomarkers because parasitized erythrocytes become specifically rigidified and this effect is potentiated by anti-malarial compounds, such as chloroquine and artesunate. This biophysical biomarker is particularly relevant because of the mechanistic link between cell deformability and enhanced splenic clearance of parasitized erythrocytes.MethodsRecently a microfluidic mechanism, called the multiplexed fluidic plunger that provides sensitive and rapid measurement of single red blood cell deformability was developed. Here it was systematically used to evaluate the deformability changes of late-stage trophozoite-infected red blood cells (iRBCs) after treatment with established clinical and pre-clinical anti-malarial compounds.ResultsIt was found that rapid and specific iRBC rigidification was a universal outcome of all but one of these drug treatments. The greatest change in iRBC rigidity was observed for (+)-SJ733 and NITD246 spiroindolone compounds, which target the Plasmodium falciparum cation-transporting ATPase ATP4. As a proof-of-principle, compounds of the bisindole alkaloid class were screened, where cladoniamide A was identified based on rigidification of iRBCs and was found to have previously unreported anti-malarial activity with an IC50 lower than chloroquine.ConclusionThese results demonstrate that rigidification of iRBCs may be used as a biomarker for anti-malarial drug efficacy, as well as for new drug screening. The novel anti-malarial properties of cladoniamide A were revealed in a proof-of-principle drug screen.

Microfluidic Technologies for Deformability-Based Cell Sorting

There are many situations in medicine and biology where it is desirable to distinguish specific cells within a population based on their mechanical deformability, which can potentially serve as a proxy for morphology or pathology. This biophysical characteristic is particularly relevant for cells in the circulatory system because deformability determines the capacity for these cells to transit through the microvasculature. These circulating cells include the abundant hematological cells such as erythrocytes (red blood cells, RBCs) and leukocytes (white blood cells, WBCs), as well as rare cells, such as circulating tumor cells (CTCs). Since deformability is such a fundamental characteristic of blood cells, deviations in normal cell deformability can contribute to a range of pathological conditions and potentially serve as a biomarker to evaluate them during treatment. In this chapter, we first discuss the role of deformability in circulating cells, including erythrocytes, leukocytes, and CTCs. We then briefly introduce our recent efforts in measuring cell deformability, and then compare the deformability of various circulating cells. Subsequently, we review the principles and applications of established strategies for deformability-based cell separation, including hydrodynamic chromatography and microfiltration. Finally, we will describe a recently developed method to sort cells based on deformability using the microfluidic ratchet mechanism, as well as its application in deformability-based separation of CTCs and deformability-based sorting of RBC infected with P. falciparum, the parasite that causes malaria.

Microfluidic Separation of Circulating Tumor Cells Based on Size and Deformability

Circulating tumor cells (CTCs) have been implicated as the seeds of cancer metastasis and therefore have the potential to provide significant prognostic and diagnostic values. Here, we describe a procedure for separating CTCs from whole blood based on size and deformability using the microfluidic ratchet device. This device leverages the ratcheting motion of single cells created as they are deformed through funnel-shaped constrictions using oscillatory flow in order to divert cells based on differences in size and deformability. Subsequent methods for CTC identification and enumeration using immunofluorescence after separation are also described.