Phenotype independent capture of circulating tumor cells using magnetic probes

K. Morris, C. Bilynsky, A-L. Papa
The George Washington University,
United States

Keywords: cancer, metastasis, CTCs, platelets


Metastasis is the leading cause of cancer related deaths. Circulating tumors cells (CTCs) that have shed from the primary tumor and have entered the bloodstream are critical for metastatic progression in cancer patients. Because CTCs can be valuable for patient diagnosis, patient prognosis, and patient therapy, CTCs are an essential biomarker for cancer progression and metastatic disease (Ju et al., Biomark Res, 2022; Jiang at al., Biomark Res, 2021). The epithelial to mesenchymal transition (EMT) is the process by which cancer cells assume a more aggressive phenotype and gain enhanced invasive and migratory properties (Jiang at al., 2021). Currently, the CELLSEARCH® Circulating Tumor Cell Test and CELLSEARCH® system is the only FDA approved test for the identifying, isolating, and enumerating CTCs from a liquid biopsy (Dirix et al., Breast Cancer Res Treat, 2022). However, because CELLSEARCH® only identifies CTCs with positive EpCAM expression, it is not applicable for detecting CTCs of a non-epithelial phenotype (i.e. mesenchymal phenotype or CTCs in between epithelial and mesenchymal states) that have little to no EpCAM expression. In addition to their primary role of maintaining hemostasis, platelets have a significant role in metastatic progression (Morris et al., Biochim. Biophys Acta (BBA), 2022). Platelets interact with CTCs immediately after CTCs enter the bloodstream, thus promoting CTC survival and promoting CTC arrest in the vasculature (Morris et al., 2022; Liu et al., Crit. Rev. in Onc./Hemo., 2021). Therefore, we propose a system that leverages naturally occurring platelet and CTC interactions and thus, will be applicable for the detection of all CTCs, regardless of origin or phenotype. Our system utilizes magnetic platelet probes that are engineered using platelet decoys (Papa et al., Sci. Transl. Med., 2019) to interact with CTCs in whole blood for magnetic retrieval (Figure 1). Our system has shown effective and consistent retrieval rates of mesenchymal-like MDA-MB-231, high EpCAM MCF-7, and low EpCAM A549 (76.7 ± 10.6%, of 60.8 ± 15.6%, and 74.4 ± 16.8%, respectively) in spiked whole blood samples (Figure 2). Our results indeed demonstrate that our system is effective in isolating cancer cells of various origins and phenotypes. We aim to further elucidate the mechanisms of CTC capture via the magnetic probes and validate our system for clinical application by assessing CTC retrieval from cancer patient blood samples. We hypothesize that our system captures a significant fraction of missed cells of broader phenotypes. Thus, we will present a comparison with CTCs retrieved from cancer patient samples with both, an EpCAM-based technology and our system. A future clinical application of our system is that CTCs could undergo further characterization once captured and isolated from a patient’s liquid biopsy to aid in patient monitoring, prognosis, and personalized therapy.