David T. Ting

Circulating Breast Tumor Cells Exhibit Dynamic Changes in Epithelial and Mesenchymal Composition

Cells in Transit(ion) Epithelial-mesenchymal transition (EMT) is a developmental program that converts adherent epithelial cells to a migratory mesenchymal state. This cell-fate change has been linked to tumor metastasis in preclinical models. To investigate whether EMT occurs in human cancer, Yu et al. (p. 580) isolated circulating tumor cells (CTCs) from breast cancer patients and analyzed their expression of epithelial and mesenchymal markers by RNA–in situ hybridization and RNA sequencing. Biphenotypic cells expressing both types of markers were rare in primary breast tumors but were enriched among CTCs, as were cells expressing only mesenchymal markers. Serial blood samples from one patient revealed that CTCs in the mesenchymal state declined in number when the patient responded to therapy but rebounded when the disease began to progress—a pattern repeated when a different therapy was administered. Thus, EMT may facilitate tumor cell dissemination in humans. Tumor cells circulating in the blood of cancer patients undergo a phenotypic change that may facilitate their spread. Epithelial-mesenchymal transition (EMT) of adherent epithelial cells to a migratory mesenchymal state has been implicated in tumor metastasis in preclinical models. To investigate its role in human cancer, we characterized EMT in circulating tumor cells (CTCs) from breast cancer patients. Rare primary tumor cells simultaneously expressed mesenchymal and epithelial markers, but mesenchymal cells were highly enriched in CTCs. Serial CTC monitoring in 11 patients suggested an association of mesenchymal CTCs with disease progression. In an index patient, reversible shifts between these cell fates accompanied each cycle of response to therapy and disease progression. Mesenchymal CTCs occurred as both single cells and multicellular clusters, expressing known EMT regulators, including transforming growth factor (TGF)–β pathway components and the FOXC1 transcription factor. These data support a role for EMT in the blood-borne dissemination of human breast cancer.

Circulating Tumor Cell Clusters Are Oligoclonal Precursors of Breast Cancer Metastasis

Circulating tumor cell clusters (CTC clusters) are present in the blood of patients with cancer but their contribution to metastasis is not well defined. Using mouse models with tagged mammary tumors, we demonstrate that CTC clusters arise from oligoclonal tumor cell groupings and not from intravascular aggregation events. Although rare in the circulation compared with single CTCs, CTC clusters have 23- to 50-fold increased metastatic potential. In patients with breast cancer, single-cell resolution RNA sequencing of CTC clusters and single CTCs, matched within individual blood samples, identifies the cell junction component plakoglobin as highly differentially expressed. In mouse models, knockdown of plakoglobin abrogates CTC cluster formation and suppresses lung metastases. In breast cancer patients, both abundance of CTC clusters and high tumor plakoglobin levels denote adverse outcomes. Thus, CTC clusters are derived from multicellular groupings of primary tumor cells held together through plakoglobin-dependent intercellular adhesion, and though rare, they greatly contribute to the metastatic spread of cancer.

Inertial Focusing for Tumor Antigen–Dependent and –Independent Sorting of Rare Circulating Tumor Cells

A multistage microfluidic chip is capable of sorting rare EpCAM+ and EpCAM− CTCs from cancer patients’ whole blood. Positive and Negative Outcomes Usually people want the good news first, to help cope with the bad news that inevitably follows. However, patients will soon desire both the positive and the negative outcomes together, according to the latest study by Ozkumur and colleagues. These authors have developed a multistage microfluidic device that is capable of sorting rare circulating tumor cells (CTCs) that are either positive or negative for the surface antigen epithelial cell adhesion molecule (EpCAM). EpCAM+ cells found in the bloodstream have long defined the typical CTC. Many sorting technologies have been developed to enumerate EpCAM+ CTCs in cancer patient’s blood; however, these cells are not always detectable in cancers with low EpCAM expression, like triple-negative breast cancer or melanoma. Ozkumur et al. engineered an automated platform, called the “CTC-iChip,” that captured both EpCAM+ and EpCAM− cancer cells in clinical samples using a series of debulking, inertial focusing, and magnetic separation steps. The sorted CTCs could then be interrogated using standard clinical protocols, such as immunocytochemistry. The authors tested the “positive mode” of their device using whole blood from patients with prostate, lung, breast, pancreatic, and colorectal cancers. After successfully separating out the EpCAM+ CTCs, they confirmed that the cells were viable and had high-quality RNA for molecular analysis, in one example, detecting the EML4-ALK gene fusion in lung cancer. Using the “negative mode” of their device, the authors were able to capture EpCAM− CTCs from patients with metastatic breast cancer, pancreatic cancer, and melanoma. The isolated CTCs showed similar morphology when compared with primary tumor tissue from these patients, suggesting that the microfluidic device can be used for clinical diagnoses—delivering both positive and negative news at once. Ozkumur et al. also demonstrated that CTCs isolated using the iChip could be analyzed on the single-cell level. One such demonstration with 15 CTCs from a prostate cancer patient reveals marked heterogeneity in the expression of mesenchymal and stem cell markers as well as typical prostate cancer–related antigens. The CTC-iChip can therefore process large volumes of patient blood to obtain not just EpCAM+ CTCs but also the EpCAM− ones, thus giving a broader picture of an individual’s cancer status and also allowing the device to be used for more cancer types. With the ability to further analyze the molecular characteristics of CTCs, this CTC-iChip could be a promising addition to current diagnostic tools used in the clinic. Circulating tumor cells (CTCs) are shed into the bloodstream from primary and metastatic tumor deposits. Their isolation and analysis hold great promise for the early detection of invasive cancer and the management of advanced disease, but technological hurdles have limited their broad clinical utility. We describe an inertial focusing–enhanced microfluidic CTC capture platform, termed “CTC-iChip,” that is capable of sorting rare CTCs from whole blood at 107 cells/s. Most importantly, the iChip is capable of isolating CTCs using strategies that are either dependent or independent of tumor membrane epitopes, and thus applicable to virtually all cancers. We specifically demonstrate the use of the iChip in an expanded set of both epithelial and nonepithelial cancers including lung, prostate, pancreas, breast, and melanoma. The sorting of CTCs as unfixed cells in solution allows for the application of high-quality clinically standardized morphological and immunohistochemical analyses, as well as RNA-based single-cell molecular characterization. The combination of an unbiased, broadly applicable, high-throughput, and automatable rare cell sorting technology with generally accepted molecular assays and cytology standards will enable the integration of CTC-based diagnostics into the clinical management of cancer.

Ex vivo culture of circulating breast tumor cells for individualized testing of drug susceptibility

Staying one step ahead of tumors Cancer treatments require continual adjustment. A drug that works initially will lose its potency as the tumor acquires new mutations that allow it to bypass the drugs lethal effects. To stay ahead of the tumor, oncologists need a noninvasive way to collect tumor cells from patients over the course of their treatment. Analyzing the mutations in these samples may help them choose the right drugs as the tumors change. In a small study of breast cancer patients, Yu et al. show that rare tumor cells circulating in the blood can be captured in viable form and used for this purpose. Science, this issue p. 216 Mutational analysis of tumor cells isolated from the blood of cancer patients may help optimize treatment selection. Circulating tumor cells (CTCs) are present at low concentrations in the peripheral blood of patients with solid tumors. It has been proposed that the isolation, ex vivo culture, and characterization of CTCs may provide an opportunity to noninvasively monitor the changing patterns of drug susceptibility in individual patients as their tumors acquire new mutations. In a proof-of-concept study, we established CTC cultures from six patients with estrogen receptor–positive breast cancer. Three of five CTC lines tested were tumorigenic in mice. Genome sequencing of the CTC lines revealed preexisting mutations in the PIK3CA gene and newly acquired mutations in the estrogen receptor gene (ESR1), PIK3CA gene, and fibroblast growth factor receptor gene (FGFR2), among others. Drug sensitivity testing of CTC lines with multiple mutations revealed potential new therapeutic targets. With optimization of CTC culture conditions, this strategy may help identify the best therapies for individual cancer patients over the course of their disease.

RNA sequencing of pancreatic circulating tumour cells implicates WNT signalling in metastasis

Circulating tumour cells (CTCs) shed into blood from primary cancers include putative precursors that initiate distal metastases. Although these cells are extraordinarily rare, they may identify cellular pathways contributing to the blood-borne dissemination of cancer. Here, we adapted a microfluidic device for efficient capture of CTCs from an endogenous mouse pancreatic cancer model and subjected CTCs to single-molecule RNA sequencing, identifying Wnt2 as a candidate gene enriched in CTCs. Expression of WNT2 in pancreatic cancer cells suppresses anoikis, enhances anchorage-independent sphere formation, and increases metastatic propensity in vivo. This effect is correlated with fibronectin upregulation and suppressed by inhibition of MAP3K7 (also known as TAK1) kinase. In humans, formation of non-adherent tumour spheres by pancreatic cancer cells is associated with upregulation of multiple WNT genes, and pancreatic CTCs revealed enrichment for WNT signalling in 5 out of 11 cases. Thus, molecular analysis of CTCs may identify candidate therapeutic targets to prevent the distal spread of cancer.

Aberrant Overexpression of Satellite Repeats in Pancreatic and Other Epithelial Cancers

Noncoding RNAs transcribed from DNA repeats in heterochromatin are expressed at surprisingly high levels in tumors. Satellite repeats in heterochromatin are transcribed into noncoding RNAs that have been linked to gene silencing and maintenance of chromosomal integrity. Using digital gene expression analysis, we showed that these transcripts are greatly overexpressed in mouse and human epithelial cancers. In 8 of 10 mouse pancreatic ductal adenocarcinomas (PDACs), pericentromeric satellites accounted for a mean 12% (range 1 to 50%) of all cellular transcripts, a mean 40-fold increase over that in normal tissue. In 15 of 15 human PDACs, alpha satellite transcripts were most abundant and HSATII transcripts were highly specific for cancer. Similar patterns were observed in cancers of the lung, kidney, ovary, colon, and prostate. Derepression of satellite transcripts correlated with overexpression of the long interspersed nuclear element 1 (LINE-1) retrotransposon and with aberrant expression of neuroendocrine-associated genes proximal to LINE-1 insertions. The overexpression of satellite transcripts in cancer may reflect global alterations in heterochromatin silencing and could potentially be useful as a biomarker for cancer detection.

Poly(lactic acid)-poly(ethylene glycol) nanoparticles as new carriers for the delivery of plasmid DNA

The purpose of the present work was to produce and characterize poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) nanoparticles (size lower than 300 nm) containing a high loading of plasmid DNA in a free form or co-encapsulated with either poly(vinyl alcohol) (PVA) or poly(vinylpyrrolidone) (PVP). The plasmid alone or with PVA or PVP was encapsulated by two different techniques: an optimized w/o/w emulsion-solvent evaporation technique as well as by a new w/o emulsion-solvent diffusion technique. Particle size, zeta potential, plasmid DNA loading and in vitro release were determined for the three plasmid-loaded formulations. The influence of the initial plasmid loadings (5, 10, 20 microg plasmid DNA/mg PLA-PEG) on those parameters was also investigated. The plasmid loaded into the nanoparticles and released in vitro was quantified by fluorimetry and the different molecular forms were identified by gel electrophoresis. PLA-PEG nanoparticles containing plasmid DNA in a free form or co-encapsulated with PVA or PVP were obtained in the range size of 150-300 nm and with a negative zeta potential, both parameters being affected by the preparation technique. Encapsulation efficiencies were high irrespective of the presence of PVA or PVP (60-90%) and were slightly affected by the preparation technique and by the initial loading. The final plasmid DNA loading in the nanoparticles was up to 10-12 microg plasmid DNA/mg polymer. Plasmid DNA release kinetics varied depending on the plasmid incorporation technique: nanoparticles prepared by the w/o diffusion technique released their content rapidly whereas those obtained by the w/o/w showed an initial burst followed by a slow release for at least 28 days. No significant influence of the plasmid DNA loading and of the co-encapsulation of PVP or PVA on the in vitro release rate was observed. In all cases the conversion of the supercoiled form to the open circular and linear forms was detected. In conclusion, plasmid DNA can be very efficiently encapsulated, either in a free form or in combination with PVP and PVA, into PLA-PEG nanoparticles. Additionally, depending on the processing conditions, these nanoparticles release plasmid DNA either very rapidly or in a controlled manner.

Radiological and surgical implications of neoadjuvant treatment with FOLFIRINOX for locally advanced and borderline resectable pancreatic cancer.

PURPOSE On the basis of the ACCORD trial, FOLFIRINOX is effective in metastatic pancreatic adenocarcinoma (PDAC), making it a rational choice for locally advanced PDAC (LA). Aims of this study are to evaluate the accuracy of imaging in determining the resectability of PDAC and to determine the surgical and clinicopathologic outcomes of pancreatic resections after neoadjuvant FOLFIRINOX therapy. PATIENTS AND METHODS Clinicopathologic data were retrospectively collected for surgical PDAC patients receiving neoadjuvant FOLFIRINOX or no neoadjuvant therapy between April 2011 and February 2014. Americas Hepato-Pancreato-Biliary Association/Society of Surgical Oncology/Society for Surgery of the Alimentary Tract consensus guidelines defined LA and borderline. Imaging was reviewed by a blinded senior pancreatic surgeon. RESULTS Of 188 patients undergoing resection for PDAC, 40 LA/borderline received FOLFIRINOX and 87 received no neoadjuvant therapy. FOLFIRINOX resulted in a significant decrease in tumor size, yet 19 patients were still classified as LA and 9 as borderline. Despite post-FOLFIRINOX imaging suggesting continued unresectability, 92% had an R0 resection. When compared with no neoadjuvant therapy, FOLFIRINOX resulted in significantly longer operative times (393 vs 300 minutes) and blood loss (600 vs 400 mL), but significantly lower operative morbidity (36% vs 63%) and no postoperative pancreatic fistulas. Length of stay (6 vs 7 days), readmissions (20% vs 30%), and mortality were equivalent (1% vs 0%). On final pathology, the FOLFIRINOX group had a significant decrease in lymph node positivity (35% vs 79%) and perineural invasion (72% vs 95%). Median follow-up was 11 months with a significant increase in overall survival with FOLFIRINOX. CONCLUSIONS After neoadjuvant FOLFIRINOX imaging no longer predicts unresectability. Traditional pathologic predictors of survival are improved, and morbidity is decreased in comparison to patients with clearly resectable cancers at the time of presentation.

A microfluidic device for label-free, physical capture of circulating tumor cell clusters

Cancer cells metastasize through the bloodstream either as single migratory circulating tumor cells (CTCs) or as multicellular groupings (CTC clusters). Existing technologies for CTC enrichment are designed to isolate single CTCs, and although CTC clusters are detectable in some cases, their true prevalence and significance remain to be determined. Here we developed a microchip technology (the Cluster-Chip) to capture CTC clusters independently of tumor-specific markers from unprocessed blood. CTC clusters are isolated through specialized bifurcating traps under low–shear stress conditions that preserve their integrity, and even two-cell clusters are captured efficiently. Using the Cluster-Chip, we identified CTC clusters in 30–40% of patients with metastatic breast or prostate cancer or with melanoma. RNA sequencing of CTC clusters confirmed their tumor origin and identified tissue-derived macrophages within the clusters. Efficient capture of CTC clusters will enable the detailed characterization of their biological properties and role in metastasis.

RNA-Seq of single prostate CTCs implicates noncanonical Wnt signaling in antiandrogen resistance.

Circulating signals of drug resistance Cancer drugs often lose their effectiveness because tumors acquire genetic changes that confer drug resistance. Ideally, patients would be switched to a different drug before tumor growth resumes, but this requires early knowledge of how resistance arose. Miyamoto et al. have developed a non-invasive method to spot resistance by sequencing RNA transcripts in single circulating tumor cells (CTCs) (see the Perspective by Nanus and Giannakakou). For example, in prostate cancer patients, drug resistance was triggered by activation of the Wnt signaling pathway. But CTCs are rare and fragile, and the technology needs further development before it is used in clinical practice. Science, this issue p. 1351; see also p. 1283 Analysis of circulating tumor cells from prostate cancer patients reveals a mechanism that contributes to treatment failure. [Also see Perspective by Nanus and Giannakakou] Prostate cancer is initially responsive to androgen deprivation, but the effectiveness of androgen receptor (AR) inhibitors in recurrent disease is variable. Biopsy of bone metastases is challenging; hence, sampling circulating tumor cells (CTCs) may reveal drug-resistance mechanisms. We established single-cell RNA-sequencing (RNA-Seq) profiles of 77 intact CTCs isolated from 13 patients (mean six CTCs per patient), by using microfluidic enrichment. Single CTCs from each individual display considerable heterogeneity, including expression of AR gene mutations and splicing variants. Retrospective analysis of CTCs from patients progressing under treatment with an AR inhibitor, compared with untreated cases, indicates activation of noncanonical Wnt signaling (P = 0.0064). Ectopic expression of Wnt5a in prostate cancer cells attenuates the antiproliferative effect of AR inhibition, whereas its suppression in drug-resistant cells restores partial sensitivity, a correlation also evident in an established mouse model. Thus, single-cell analysis of prostate CTCs reveals heterogeneity in signaling pathways that could contribute to treatment failure.