The Mechanical Fingerprint of Circulating Tumor Cells (CTCs) in Breast Cancer Patients.

Ivonne Nel,Erik W Morawetz,Bahriye Aktas,Dimitrij Tschodu,Josef A Käs

doi:10.3390/cancers13051119

Abstract

Simple SummaryDetection of circulating tumor cells (CTCs) in the blood of cancer patients is a challenging issue, since they adapt to the biochemical and physical landscape of the bloodstream. We approached the issue of CTC identification on a biophysical level. For the first time, we recorded the mechanical deformation profiles of potential CTCs, which were isolated from the blood of breast cancer patients, at the force regime of the deforming blood flow. Mechanical fingerprints of CTCs were significantly different from healthy white blood cells. We used machine learning to further evaluate the differences and identify discrimination criteria. Our results suggest that mechanical characterization of CTCs at low forces is a promising path towards CTC detection.Circulating tumor cells (CTCs) are a potential predictive surrogate marker for disease monitoring. Due to the sparse knowledge about their phenotype and its changes during cancer progression and treatment response, CTC isolation remains challenging. Here we focused on the mechanical characterization of circulating non-hematopoietic cells from breast cancer patients to evaluate its utility for CTC detection. For proof of premise, we used healthy peripheral blood mononuclear cells (PBMCs), human MDA-MB 231 breast cancer cells and human HL-60 leukemia cells to create a CTC model system. For translational experiments CD45 negative cells—possible CTCs—were isolated from blood samples of patients with mamma carcinoma. Cells were mechanically characterized in the optical stretcher (OS). Active and passive cell mechanical data were related with physiological descriptors by a random forest (RF) classifier to identify cell type specific properties. Cancer cells were well distinguishable from PBMC in cell line tests. Analysis of clinical samples revealed that in PBMC the elliptic deformation was significantly increased compared to non-hematopoietic cells. Interestingly, non-hematopoietic cells showed significantly higher shape restoration. Based on Kelvin–Voigt modeling, the RF algorithm revealed that elliptic deformation and shape restoration were crucial parameters and that the OS discriminated non-hematopoietic cells from PBMC with an accuracy of 0.69, a sensitivity of 0.74, and specificity of 0.63. The CD45 negative cell population in the blood of breast cancer patients is mechanically distinguishable from healthy PBMC. Together with cell morphology, the mechanical fingerprint might be an appropriate tool for marker-free CTC detection.

Highlights

One reason for metastatic relapse in patients with breast cancer is hematogenous spread during early disease stages when single tumor cells detach from the primary tumor site and enter the vascular system [1]
We investigated mechanical profiles of peripheral blood mononuclear cells (PBMCs) samples from healthy donors (n = 3) compared to PBMC from breast cancer patients (n = 2)
We measured the mechanical characteristics of epithelial breast cancer cells from the highly invasive cell line MDA-MB 231, which represents a mesenchymal-like phenotype, and HL-60 leukemia cells, which are naturally habitant in blood

Summary

Introduction

One reason for metastatic relapse in patients with breast cancer is hematogenous spread during early disease stages when single tumor cells detach from the primary tumor site and enter the vascular system [1]. Circulating tumor cells (CTCs) in the blood might be useful as predictive markers to monitor treatment response in the clinical setting and the risk of relapse through distant metastasis Their ability to change phenotypical, mechanical and functional properties during cancer growth and treatment leads to a variety of subpopulations that complicate the use of CTCs as a biomarker. CTCs are supposed to have a negative counterstain against the leucocyte marker CD45 and a positive nuclear DNA staining This approach is complicated and assumes that CTCs express the same molecules as the host tissue. Morphological criteria define cancer cells as cells with an enlarged nucleus-to-cytoplasm ratio and a large cell size [21] These cytological properties are associated with altered mechanical characteristics such as dynamic modification of the cytoskeletal stiffness [22]. Mechanical and functional changes during cancer progression and treatment, isolation of CTC subpopulations remains challenging and cannot be guided by the phenotype alone; cell mechanics have to be considered

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