The metastatic dissemination and spread of malignant circulating tumor cells (CTCs) accounts for more than 90% of cancer-related deaths. CTCs detach from a primary tumor, travel through the circulatory system, and then invade and proliferate in distant organs. The detection of CTCs from blood has been established for prognostic monitoring and is predictive of patient outcome. Analysis of CTCs could enable the means for early detection and screening in cancer, as well as provide diagnostic access to tumor tissues in a minimally invasive way. The fundamental challenge with analyzing CTCs is the fact that they occur at extremely low concentrations in blood, on the order of one out of a billion cells. Various technologies have been proposed to isolate CTCs for enrichment. Here we focus on antigen-independent approaches that are not limited by specific capture antibodies. Intrinsic physical properties of CTCs, including cell size, deformability, and electrical properties, are reviewed, and technologies developed to exploit them for enrichment from blood are summarized. Physical enrichment technologies are of particular interest as they have the potential to increase yield and enable the analysis of rare CTC phenotypes that may not be otherwise obtained.

Introduction: PARP inhibitors have shown promising results in early studies for treatment of breast cancer susceptibility gene (BRCA)–deficient breast cancers; however, resistance ultimately develops. Furthermore, the benefit of PARP inhibitors (PARPi) in triple-negative breast cancers (TNBC) remains unknown. Recent evidence indicates that in TNBCs, cells that display “cancer stem cell” properties are resistant to conventional treatments, mediate tumor metastasis, and contribute to recurrence. The sensitivity of breast cancer stem cells (CSC) to PARPi is unknown. Experimental Design: We determined the sensitivity of breast CSCs to PARP inhibition in BRCA1-mutant and -wild-type TNBC cell lines and tumor xenografts. We also investigated the role of RAD51 in mediating CSC resistance to PARPi in these in vitro and in vivo models. Results: We demonstrated that the CSCs in BRCA1-mutant TNBCs were resistant to PARP inhibition, and that these cells had both elevated RAD51 protein levels and activity. Downregulation of RAD51 by shRNA sensitized CSCs to PARP inhibition and reduced tumor growth. BRCA1–wild-type cells were relatively resistant to PARP inhibition alone, but reduction of RAD51 sensitized both CSC and bulk cells in these tumors to PARPi treatment. Conclusions: Our data suggest that in both BRCA1-mutant and BRCA1–wild-type TNBCs, CSCs are relatively resistant to PARP inhibition. This resistance is mediated by RAD51, suggesting that strategies aimed at targeting RAD51 may increase the therapeutic efficacy of PARPi. Clin Cancer Res; 23(2); 514–22. ©2016 AACR.

During development, the mammary gland undergoes extensive remodeling driven by stem cells. Breast cancers are also hierarchically organized and driven by cancer stem cells characterized by CD44+CD24low/- or aldehyde dehydrogenase (ALDH) expression. These markers identify mesenchymal and epithelial populations both capable of tumor initiation. Less is known about these populations in non-cancerous mammary glands. From RNA sequencing, ALDH+ and ALDH-CD44+CD24- human mammary cells have epithelial-like and mesenchymal-like characteristics, respectively, with some co-expressing ALDH+ and CD44+CD24- by flow cytometry. At the single-cell level, these cells have the greatest mammosphere-forming capacity and express high levels of stemness and epithelial-to-mesenchymal transition-associated genes including ID1, SOX2, TWIST1, and ZEB2. We further identify single ALDH+ cells with a hybrid epithelial/mesenchymal phenotype that express genes associated with aggressive triple-negative breast cancers. These results highlight single-cell analyses to characterize tissue heterogeneity, even in marker-enriched populations, and identify genes and pathways that define this heterogeneity.

BACKGROUND: The dissemination of circulating tumor cells (CTCs) that cause metastases in distant organs accounts for the majority of cancer-related deaths. CTCs have been established as a cancer biomarker of known prognostic value. The enrichment of viable CTCs for ex vivo analysis could further improve cancer diagnosis and guide treatment selection. We designed a new flexible micro spring array (FMSA) device for the enrichment of viable CTCs independent of antigen expression. METHODS: Unlike previous microfiltration devices, flexible structures at the micro scale minimize cell damage to preserve viability, while maximizing throughput to allow rapid enrichment directly from whole blood with no need for sample preprocessing. Device performance with respect to capture efficiency, enrichment against leukocytes, viability, and proliferability was characterized. CTCs and CTC microclusters were enriched from clinical samples obtained from breast, lung, and colorectal cancer patients. RESULTS: The FMSA device enriched tumor cells with 90% capture efficiency, higher than 104 enrichment, and better than 80% viability from 7.5-mL whole blood samples in <10 min on a 0.5-cm2 device. The FMSA detected at least 1 CTC in 16 out of 21 clinical samples (approximately 76%) compared to 4 out of 18 (approximately 22%) detected with the commercial CellSearch® system. There was no incidence of clogging in over 100 tested fresh whole blood samples. CONCLUSIONS: The FMSA device provides a versatile platform capable of viable enrichment and analysis of CTCs from clinically relevant volumes of whole blood.