Circulating Tumor Cell Clustering Shapes DNA Methylation to Enable Metastasis Seeding.

The ability of circulating tumor cells (CTCs) to form clusters has been linked to increased metastatic potential. Yet biological features and vulnerabilities of CTC clusters remain largely unknown. Here, we profile the DNA methylation landscape of single CTCs and CTC clusters from breast cancer patients and mouse models on a genome-wide scale. We find that binding sites for stemness- and proliferation-associated transcription factors are specifically hypomethylated in CTC clusters, including binding sites for OCT4, NANOG, SOX2, and SIN3A, paralleling embryonic stem cell biology. Among 2,486 FDA-approved compounds, we identify Na+/K+ ATPase inhibitors that enable the dissociation of CTC clusters into single cells, leading to DNA methylation remodeling at critical sites and metastasis suppression. Thus, our results link CTC clustering to specific changes in DNA methylation that promote stemness and metastasis and point to cluster-targeting compounds to suppress the spread of cancer.

Neutrophils escort circulating tumour cells to enable cell cycle progression.

A better understanding of the features that define the interaction between cancer cells and immune cells is important for the development of new cancer therapies1. However, focus is often given to interactions that occur within the primary tumour and its microenvironment, whereas the role of immune cells during cancer dissemination in patients remains largely uncharacterized2,3. Circulating tumour cells (CTCs) are precursors of metastasis in several types of cancer4-6, and are occasionally found within the bloodstream in association with non-malignant cells such as white blood cells (WBCs)7,8. The identity and function of these CTC-associated WBCs, as well as the molecular features that define the interaction between WBCs and CTCs, are unknown. Here we isolate and characterize individual CTC-associated WBCs, as well as corresponding cancer cells within each CTC-WBC cluster, from patients with breast cancer and from mouse models. We use single-cell RNA sequencing to show that in the majority of these cases, CTCs were associated with neutrophils. When comparing the transcriptome profiles of CTCs associated with neutrophils against those of CTCs alone, we detect a number of differentially expressed genes that outline cell cycle progression, leading to more efficient metastasis formation. Further, we identify cell-cell junction and cytokine-receptor pairs that define CTC-neutrophil clusters, representing key vulnerabilities of the metastatic process. Thus, the association between neutrophils and CTCs drives cell cycle progression within the bloodstream and expands the metastatic potential of CTCs, providing a rationale for targeting this interaction in treatment of breast cancer.

Computational Analysis of DNA and RNA Sequencing Data Obtained from Liquid Biopsies.

Next-generation sequencing of DNA and RNA obtained from liquid biopsies of cancer patients may reveal important insights into disease progression and metastasis formation, and it holds the promise to enable new methods for noninvasive screening and clinical decision support. However, implementing liquid biopsy sequencing protocols is challenged by capturing circulating tumor cells or cell-free tumor DNA from blood samples, by amplifying genomic DNA and RNA in a reliable and unbiased manner, and by extracting biologically meaningful signals from the noisy sequencing data. In this chapter, we discuss computational methods for the analysis of DNA and RNA sequencing data obtained from liquid biopsies, addressing these challenges.

Denosumab treatment is associated with the absence of circulating tumor cells in patients with breast cancer.

BACKGROUND: The presence of circulating tumor cells (CTCs) in patients with breast cancer correlates to a bad prognosis. Yet, CTCs are detectable in only a minority of patients with progressive breast cancer, and factors that influence the abundance of CTCs remain elusive. METHODS: We conducted CTC isolation and enumeration in a selected group of 73 consecutive patients characterized by progressive invasive breast cancer, high tumor load and treatment discontinuation at the time of CTC isolation. CTCs were quantified with the Parsortix microfluidic device. Clinicopathological variables, blood counts at the time of CTC isolation and detailed treatment history prior to blood sampling were evaluated for each patient. RESULTS: Among 73 patients, we detected at least one CTC per 7.5 ml of blood in 34 (46%). Of these, 22 (65%) had single CTCs only, whereas 12 (35%) featured both single CTCs and CTC clusters. Treatment with the monoclonal antibody denosumab correlated with the absence of CTCs, both when considering all patients and when considering only those with bone metastasis. We also found that low red blood cell count was associated with the presence of CTCs, whereas high CA 15-3 tumor marker, high mean corpuscular volume, high white blood cell count and high mean platelet volume associated specifically with CTC clusters. CONCLUSIONS: In addition to blood count correlatives to single and clustered CTCs, we found that denosumab treatment associates with most patients lacking CTCs from their peripheral circulation. Prospective studies will be needed to validate the involvement of denosumab in the prevention of CTC generation.

Detection of circulating tumour cell clusters in human glioblastoma.

Human glioblastoma (GBM) is a highly aggressive, invasive and hypervascularised malignant brain cancer. Individual circulating tumour cells (CTCs) are sporadically found in GBM patients, yet it is unclear whether multicellular CTC clusters are generated in this disease and whether they can bypass the physical hurdle of the blood-brain barrier.  Here, we assessed CTC presence and composition at multiple time points in 13 patients with progressing GBM during an open-label phase 1/2a study with the microtubule inhibitor BAL101553. We observe CTC clusters ranging from 2 to 23 cells and present at multiple sampling time points in a GBM patient with pleomorphism and extensive necrosis, throughout disease progression. Exome sequencing of GBM CTC clusters highlights variants in 58 cancer-associated genes including ATM, PMS2, POLE, APC, XPO1, TFRC, JAK2, ERBB4 and ALK. Together, our findings represent the first evidence of the presence of CTC clusters in GBM.

Prospective observational study of the role of the microbiome in BCG responsiveness prediction (SILENT-EMPIRE): a study protocol.

INTRODUCTION: The human microbiota, the community of micro-organisms in different cavities, has been increasingly linked with inflammatory and neoplastic diseases. While investigation into the gut microbiome has been robust, the urinary microbiome has only recently been described. Investigation into the relationship between bladder cancer (BC) and the bladder and the intestinal microbiome may elucidate a pathophysiological relationship between the two. The bladder or the intestinal microbiome or the interplay between both may also act as a non-invasive biomarker for tumour behaviour. While these associations have not yet been fully investigated, urologists have been manipulating the bladder microbiome for treatment of BC for more than 40 years, treating high grade non-muscle invasive BC (NMIBC) with intravesical BCG immunotherapy. Neither the association between the microbiome sampled directly from bladder tissue and the response to BCG-therapy nor the association between response to BCG-therapy with the faecal microbiome has been studied until now. A prognostic tool prior to initiation of BCG-therapy is still needed. METHODS AND ANALYSIS: In patients with NMIBC bladder samples will be collected during surgery (bladder microbiome assessment), faecal samples (microbiome assessment), instrumented urine and blood samples (biobank) will also be taken. We will analyse the microbial community by 16S rDNA gene amplicon sequencing. The difference in alpha diversity (diversity of species within each sample) and beta diversity (change in species diversity) between BCG-candidates will be assessed. Subgroup analysis will be performed which will lead to the development of a clinical prediction model estimating risk of BCG-response. ETHICS AND DISSEMINATION: The study has been approved by the Cantonal Ethics Committee Zurich (2021-01783) and it is being conducted in accordance with the Declaration of Helsinki and Good Clinical Practice. Study results will be disseminated through peer-reviewed journals and national and international scientific conferences. TRIAL REGISTRATION NUMBER: NCT05204199.

Multi-color clonal tracking reveals intra-stage proliferative heterogeneity during mammary tumor progression.

Despite major progress in breast cancer research, the functional contribution of distinct cancer cell clones to malignant tumor progression and metastasis remains largely elusive. We have assessed clonal heterogeneity within individual primary tumors and metastases and also during the distinct stages of malignant tumor progression using clonal tracking of cancer cells in the MMTV-PyMT mouse model of metastatic breast cancer. Comparative gene expression analysis of clonal subpopulations reveals a substantial level of heterogeneity across and also within the various stages of breast carcinogenesis. The intra-stage heterogeneity is primarily manifested by differences in cell proliferation, also found within invasive carcinomas of luminal A-, luminal B-, and HER2-enriched human breast cancer. Surprisingly, in the mouse model of clonal tracing of cancer cells, chemotherapy mainly targets the slow-proliferative clonal populations and fails to efficiently repress the fast-proliferative populations. These insights may have considerable impact on therapy selection and response in breast cancer patients.

Quantification of Protein Secretion from Circulating Tumor Cells in Microfluidic Chambers.

Cancer cells can be released from a cancerous lesion and migrate into the circulatory system, from whereon they may form metastases at distant sites. Today, it is possible to infer cancer progression and treatment efficacy by determining the number of circulating tumor cells (CTCs) in the patient's blood at multiple time points; further valuable information about CTC phenotypes remains inaccessible. In this article, a microfluidic method for integrated capture, isolation, and analysis of membrane markers as well as quantification of proteins secreted by single CTCs and CTC clusters is introduced. CTCs are isolated from whole blood with extraordinary efficiencies above 95% using dedicated trapping structures that allow co-capture of functionalized magnetic beads to assess protein secretion. The patform is tested with multiple breast cancer cell lines spiked into human blood and mouse-model-derived CTCs. In addition to immunostaining, the secretion level of granulocyte growth stimulating factor (G-CSF), which is shown to be involved in neutrophil recruitment, is quantified The bead-based assay provides a limit of detection of 1.5 ng mL-1 or less than 3700 molecules per cell. Employing barcoded magnetic beads, this platform can be adapted for multiplexed analysis and can enable comprehensive functional CTC profiling in the future.

Hypoxia Triggers the Intravasation of Clustered Circulating Tumor Cells.

Circulating tumor cells (CTCs) are shed from solid cancers in the form of single or clustered cells, and the latter display an extraordinary ability to initiate metastasis. Yet, the biological phenomena that trigger the shedding of CTC clusters from a primary cancerous lesion are poorly understood. Here, when dynamically labeling breast cancer cells along cancer progression, we observe that the majority of CTC clusters are undergoing hypoxia, while single CTCs are largely normoxic. Strikingly, we find that vascular endothelial growth factor (VEGF) targeting leads to primary tumor shrinkage, but it increases intra-tumor hypoxia, resulting in a higher CTC cluster shedding rate and metastasis formation. Conversely, pro-angiogenic treatment increases primary tumor size, yet it dramatically suppresses the formation of CTC clusters and metastasis. Thus, intra-tumor hypoxia leads to the formation of clustered CTCs with high metastatic ability, and a pro-angiogenic therapy suppresses metastasis formation through prevention of CTC cluster generation.