Functional profiling of circulating tumor cells with an integrated vortex capture and single-cell protease activity assay

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Abstract

<p id="d5572592e276">The current paradigm in liquid biopsies focuses on circulating tumor cell (CTC) count and genomics to provide clinically actionable information. We push beyond current capabilities to introduce a functional assay that quantifies protease secretion from live CTCs with single-cell resolution. In this assay, an integrated microfluidic device captures CTCs from blood and washes and encapsulates them into nanoliter-scale droplets with fluorogenic substrates within minutes, maintaining physiologic conditions. Our data support the presence of outlier CTCs with high protease activity that may drive metastasis or immune evasion. We reveal an intriguing correlation between CTC protease activity and metastatic progression. Such functional liquid biopsy approaches provide avenues to understand the metastatic process and potential for companion diagnostics. </p><p class="first" id="d5572592e279">Tumor cells are hypothesized to use proteolytic enzymes to facilitate invasion. Whether circulating tumor cells (CTCs) secrete these enzymes to aid metastasis is unknown. A quantitative and high-throughput approach to assay CTC secretion is needed to address this question. We developed an integrated microfluidic system that concentrates rare cancer cells >100,000-fold from 1 mL of whole blood into ∼50,000 2-nL drops composed of assay reagents within 15 min. The system isolates CTCs by size, exchanges fluid around CTCs to remove contaminants, introduces a matrix metalloprotease (MMP) substrate, and encapsulates CTCs into microdroplets. We found CTCs from prostate cancer patients possessed above baseline levels of MMP activity (1.7- to 200-fold). Activity of CTCs was generally higher than leukocytes from the same patient (average CTC/leukocyte MMP activity ratio, 2.6 ± 1.5). Higher MMP activity of CTCs suggests active proteolytic processes that may facilitate invasion or immune evasion and be relevant phenotypic biomarkers enabling companion diagnostics for anti-MMP therapies. </p>

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Antibody-mediated inhibition of MICA and MICB shedding promotes NK cell–driven tumor immunity

Bettina Franz, Kai Wucherpfennig, Lucas Ferrari de Andrade … (2018)

MICA and MICB are expressed by many human cancers as a result of cellular stress, and can tag cells for elimination by cytotoxic lymphocytes through natural killer group 2D (NKG2D) receptor activation. However, tumors evade this immune recognition pathway through proteolytic shedding of MICA and MICB proteins. We rationally designed antibodies targeting the MICA α 3 domain, the site of proteolytic shedding, and found that these antibodies prevented loss of cell surface MICA and MICB by human cancer cells. These antibodies inhibited tumor growth in multiple fully immunocompetent mouse models and reduced human melanoma metastases in a humanized mouse model. Antitumor immunity was mediated mainly by natural killer (NK) cells through activation of NKG2D and CD16 Fc receptors. This approach prevents the loss of important immunostimulatory ligands by human cancers and reactivates antitumor immunity.

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Circulating tumor cell number and prognosis in progressive castration-resistant prostate cancer.

Daniel Danila, Glenn Heller, Gretchen Gignac … (2007)

The development of tumor-specific markers to select targeted therapies and to assess clinical outcome remains a significant area of unmet need. We evaluated the association of baseline circulating tumor cell (CTC) number with clinical characteristics and survival in patients with castrate metastatic disease considered for different hormonal and cytotoxic therapies. CTC were isolated by immunomagnetic capture from 7.5-mL samples of blood from 120 patients with progressive clinical castrate metastatic disease. We estimated the probability of survival over time by the Kaplan-Meier method. The concordance probability estimate was used to gauge the discriminatory strength of the informative prognostic factors. Sixty-nine (57%) patients had five or more CTC whereas 30 (25%) had two cells or less. Higher CTC numbers were observed in patients with bone metastases relative to those with soft tissue disease and in patients who had received prior cytotoxic chemotherapy relative to those who had not. CTC counts were modestly correlated to measurements of tumor burden such as prostate-specific antigen and bone scan index, reflecting the percentage of boney skeleton involved with tumor. Baseline CTC number was strongly associated with survival, without a threshold effect, which increased further when baseline prostate-specific antigen and albumin were included. Baseline CTC was predictive of survival, with no threshold effect. The shedding of cells into the circulation represents an intrinsic property of the tumor, distinct from extent of disease, and provides unique information relative to prognosis.

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Circulating tumor cell detection predicts early metastatic relapse after neoadjuvant chemotherapy in large operable and locally advanced breast cancer in a phase II randomized trial.

Suzette Delaloge, Jean-Yves Pierga, Etienne Brain … (2008)

Circulating tumor cells in blood from metastatic breast cancer patients have been reported as a surrogate marker for tumor response and shorter survival. The aim of this study was to determine whether circulating tumor cells are present in the blood of patients with large operable or locally advanced breast cancer before neoadjuvant chemotherapy and after neoadjuvant chemotherapy before surgery. Blood samples of 7.5 mL were obtained on CellSave tubes from patients included in a phase II trial (REMAGUS 02). Circulating tumor cells were immunomagnetically separated and fluorescently stained by the CellSearch system. Blood from 20 metastatic breast cancer patients was used as a positive control. From October 2004 to July 2006, preneoadjuvant chemotherapy and/or postneoadjuvant chemotherapy blood samples were obtained from 118 patients. At least 1 circulating tumor cell was detected in 22 of 97 patients with preneoadjuvant chemotherapy samples (23%; 95% confidence interval, 15-31%; median, 2 cells; range, 1-17 cells). Circulating tumor cell positivity rates were 17% in 86 postneoadjuvant chemotherapy samples and 27% in all 118 patients. Persistence of circulating tumor cells at the end of neoadjuvant chemotherapy was not correlated with treatment response. After a short median follow-up of 18 months, the presence of circulating tumor cells (P=0.017), hormone receptor negativity, and large tumor size were independent prognostic factors for shorter distant metastasis-free survival. Circulating tumor cells can be detected by the CellSearch system at a low cutoff of 1 cell in 27% of patients receiving neoadjuvant chemotherapy. Circulating tumor cell detection was not correlated to the primary tumor response but is an independent prognostic factor for early relapse.