Circulating tumour cells: insights into tumour heterogeneity

Generally applicable circulating tumor cell enrichment and identification through a membrane glycoprotein-targeting strategy combining magnetic isolation and biological orthogonality labeling

Although the importance of circulating tumor cells (CTCs) has been widely recognized, it is still a challenge to realize high-efficiency and accurate enrichment and identification of highly heterogeneous CTCs derived from various types of tumors in complex cancer processes. Currently, the most widely used methods follow the general idea of sequential immunoaffinitive capture and immunostaining to achieve the abovementioned goal. However, different organ/tissue origins as well as the inherent heterogeneity of CTCs would lead to the missed detection of certain CTC subtypes using such methods. Further, immunocytochemistry (ICC) immunostaining disrupts the physiological structure of cells, severely limiting the detection and application scenarios that require the participation of live cells. To address these limitations, we have developed a generally applicable strategy for the isolation and labeling of CTCs. This strategy focuses on targeting the universal characteristics of all tumor cells, specifically the abnormally expressed cell membrane glycoproteins, such as the transferrin receptor and sialic acid. Strategically, transferrin-functionalized magnetic beads (TMBs) were applied to enrich CTCs, and azide-based bioorthogonal chemistry was employed to label target CTCs. Accordingly, the membrane glycoprotein-targeting strategy achieved unbiased enrichment and labeling of broad-spectrum CTCs that were both epithelial and non-epithelial phenotypic populations with varied organ/tissue origins (MCF-7, HepG2, A549, Jurkat, and B16), with a capture efficiency of >95% and a detection limit as low as 5 cells per mL in artificial blood. In particular, our developed strategy displayed excellent specificity, and the CTCs under capture and fluorescence labelling remained with good viability and could be further cultivated and analyzed. Finally, the membrane glycoprotein-targeting strategy successfully detected and identified 33-223 CTCs from 1 mL patient blood samples.

Combination of multiple nucleic acid aptamers for precision detection of tumors based on optical methods

BACKGROUND AND PURPOSE

Nucleic acid aptamers are a novel molecular recognition tool that is functionally similar to antibodies but superior to antibodies in terms of thermal stability, structural modification, preparation, and cost, and therefore hold great promise for molecular detection. However, due to the limitations of a single aptamer in molecular detection, the multiple aptamer combination for bioanalysis has received much attention. Here, we reviewed the progress of tumor precision detection based on the combination of multiple nucleic acid aptamers and optical methods and discussed its challenges and prospects.

METHODS

The relevant literature in PubMed was collected and reviewed.

RESULTS

The combination of two or more aptamers with modern nanomaterials and analytical methods allows the fabrication of various detection systems for the simultaneous detection of different structural domains of a substance and/or different substances, including soluble tumor markers, tumor cell surface and intracellular markers, circulating tumor cells, and other tumor-related biomolecules, which has great potential for application in efficient and precise tumor detection.

CONCLUSION

The combination of multiple nucleic acid aptamers provides a new approach for the precise detection of tumors and will play an important role in precision medicine for tumors.

Mutant-allele dispersion correlates with prognosis risk in patients with advanced non-small cell lung cancer

BACKGROUND

Intra-tumor heterogeneity (ITH) contributes to lung cancer progression and resistance to therapy. To evaluate ITH and determine whether it may be employed as a predictive biomarker of prognosis in patients with advanced non-small cell lung cancer (NSCLC), we used a novel algorithm called mutant-allele dispersion (MAD).

METHODS

In the study, 103 patients with advanced NSCLC were enrolled. Using a panel of 425 cancer-related genes, next-generation sequencing (NGS) was performed on tumor specimens that had been collected. From NGS data, we derived MAD values, and we next looked into their relationships with clinical variables and different mutation subtypes.

RESULTS

The median MAD among 103 NSCLC patients was 0.73. EGFR mutation, tyrosine kinase inhibitor (TKI) therapy, radiotherapy, and chemotherapy cycles were all substantially correlated with the MAD score. In patients with lung adenocarcinoma (LUAD), correlation analysis revealed that the MAD score was substantially linked with Notch pathway mutation (P = 0.021). A significant relationship between high MAD and shorter progression-free survival (PFS) was found (HR = 2.004, 95%CI 1.269-3.163, P = 0.003). In patients with advanced NSCLC, histological type (P = 0.004), SMARCA4 mutation (P = 0.038), and LRP1B mutation (P = 0.006) were all independently associated with prognosis. The disease control rate was considerably greater in the low MAD group compared to the high MAD group in 19 LUAD patients receiving immunotherapy (92.9% vs. 40%, P = 0.037). TKI-PFS was longer in 37 patients with low MAD who received first-line TKI therapy (P = 0.014).

CONCLUSION

Our findings suggested that MAD is a practical and simple algorithm for assessing ITH, and populations with high MAD values are more likely to have EGFR mutations. MAD can be used as a potential biomarker to predict not only the prognosis of NSCLC but also the efficacy of immunotherapy and TKI therapy in patients with advanced NSCLC.

Chemokines in Triple-Negative Breast Cancer Heterogeneity: New Challenges for Clinical Implications

Tumor heterogeneity is a hallmark of cancer and one of the primary causes of resistance to therapies. Triple-negative breast cancer (TNBC), which accounts for 15% to 20% of all breast cancers and is the most aggressive subtype, is very diverse, connected to metastatic potential and response to therapy. It is a very diverse disease at the molecular, pathologic, and clinical levels. TNBC is substantially more likely to recur and has a worse overall survival rate following diagnosis than other breast cancer subtypes. Chemokines, low molecular weight proteins that stimulate chemotaxis, have been shown to control the cues responsible for TNBC heterogeneity. In this review, we have focused on tumor heterogeneity and the role of chemokines in modulating tumor heterogeneity, since this is the most critical issue in treating TNBC. Additionally, we examined numerous cues mediated by chemokine networks that contribute to the heterogeneity of TNBC. Recent developments in our knowledge of the chemokine networks that regulate TNBC heterogeneity may pave the door for developing difficult-to-treat TNBC treatment options.

Seeding metastases: The role and clinical utility of circulating tumour cells

Peripheral human blood is a readily-accessible source of patient material in which circulating tumour cells (CTCs) can be found. Their isolation and characterization holds the potential to provide prognostic value for various solid cancers. Enumeration of CTCs from blood is becoming a common practice in informing prognosis and may guide therapy decisions. It is further recognized that enumeration alone does not capture perspective on the heterogeneity of tumours and varying functional abilities of the CTCs to interact with the secondary microenvironment. Characterizing the isolated CTCs further, in particular assessing their functional abilities, can track molecular changes in the disease progress. As a step towards identifying a suite of functional features of CTCs that could aid in clinical decisions, developing a CTC isolation technique based on extracellular matrix (ECM) interactions may provide a more solid foundation for isolating the cells of interest. Techniques based on size, charge, density, and single biomarkers are not sufficient as they underutilize other characteristics of cancer cells. The ability of cancer cells to interact with ECM proteins presents an opportunity to utilize their full character in capturing, and also allows assessment of the features that reveal how cells might behave at secondary sites during metastasis. This article will review some common techniques and recent advances in CTC capture technologies. It will further explore the heterogeneity of the CTC population, challenges they experience in their metastatic journey, and the advantages of utilizing an ECM-based platform for CTC capture. Lastly, we will discuss how tailored ECM approaches may present an optimal platform to capture an influential heterogeneous population of CTCs.

A double-tetrahedral DNA framework based electrochemical biosensor for ultrasensitive detection and release of circulating tumor cells

Detecting circulating tumor cells (CTCs) in patients' blood is essential for early diagnosis, precise treatment and prognosis of cancer. Yet due to CTCs being extremely rare in the peripheral blood of patients, it is still a challenge to detect CTCs with high sensitivity and high selectivity. Here, we developed a double-tetrahedral DNA framework (DTDF) based electrochemical biosensor system (E-CTC sensor system) for ultrasensitive detection and release of CTCs. In this work, an upright tetrahedral DNA framework (UTDF) was used as a rigid scaffold to modify a screen-printed gold electrode (SPGE), and an inverted tetrahedral DNA framework (ITDF) provided three vertex chains to multivalently bind with aptamers. Meanwhile, a streptavidin tagged horseradish peroxidase homopolymer (SA-polyHRP) was linked to biotin-modified aptamers to significantly amplify the signal. Moreover, the captured CTCs could be effectively released via benzonase nuclease with little cell damage. Our E-CTC sensor system achieved a linear range from 1 to 10⁵ MCF-7 cells with an ultralow detection limit of 1 cell. The release efficiency reached 88.1%-97.6% and the viability of the released cells reached up to 98%. We also detected the MCF-7 cells in mimic whole blood samples, suggesting that the E-CTC sensor system shows promise for use in clinical research.

Using single-cell sequencing technology to detect circulating tumor cells in solid tumors

Circulating tumor cells are tumor cells with high vitality and high metastatic potential that invade and shed into the peripheral blood from primary solid tumors or metastatic foci. Due to the heterogeneity of tumors, it is difficult for high-throughput sequencing analysis of tumor tissues to find the genomic characteristics of low-abundance tumor stem cells. Single-cell sequencing of circulating tumor cells avoids interference from tumor heterogeneity by comparing the differences between single-cell genomes, transcriptomes, and epigenetic groups among circulating tumor cells, primary and metastatic tumors, and metastatic lymph nodes in patients' peripheral blood, providing a new perspective for understanding the biological process of tumors. This article describes the identification, biological characteristics, and single-cell genome-wide variation in circulating tumor cells and summarizes the application of single-cell sequencing technology to tumor typing, metastasis analysis, progression detection, and adjuvant therapy.

Automated enumeration and phenotypic characterization of CTCs and tdEVs in patients with metastatic castration resistant prostate cancer

Background

Although most patients with metastatic castration-resistant prostate cancer (mCRPC) initially benefit from treatment with androgen receptor signaling inhibitors (ARSi), resistance inevitably occurs. Hence, we investigated the prognostic value of automated circulating tumor cell (CTC) and tumor-derived extracellular vesicle (tdEV) enumeration and their dynamics, in patients with mCRPC in the context of the initiation of treatment with ARSi. Furthermore, we hypothesize that CTC phenotypic heterogeneity might serve as a measurable biomarker under these circumstances.

Methods

Using an image analysis tool, we reanalyzed all CellSearch images previously acquired in the context of a prospective, multicenter clinical study for patients with mCRPC (n = 170) starting a new line of ARSi, for CTC and tdEV detection and enumeration. CTC (n = 19 129) phenotypic diversity was quantified by the Shannon index (SI). Progression-free survival (PFS) and overall survival (OS) were compared between groups of patients stratified according to CTC, tdEV, and SI levels.

Results

Automated CTC enumeration provided similar clinical prognostication compared with operator-based counts. Patients demonstrating high CTC phenotypic heterogeneity before therapy had a shorter median PFS (4.82 vs. 8.49 months, HR 1.79; P = 0.03) and OS (12.6 months vs. not reached, HR 2.32; P = 0.03), compared to patients with low diversity, irrespective of CTC level. Multivariable analysis showed how the prognostic value of the baseline SI was lost by pretreatment chemotherapy status, CTC counts, and PSA levels.

Conclusions

Automated CTC counts are a reliable substitute for reviewer-based enumeration, as they are equally informative for prognosis assessment in patients with mCRPC. Beyond enumeration, we demonstrated the added value of studying CTC phenotypic diversity for patient prognostication, warranting future investigation.

Protein glycosylation in head and neck cancers: From diagnosis to treatment

Glycosylation is the most common post-translational modification (PTM) of proteins. Malignant tumour cells frequently undergo an alteration in surface protein glycosylation. This phenomenon is also common in cancers of the head and neck, most of which are squamous cell carcinomas (HNSCC). It affects cell functions, including proliferation, motility and invasiveness, thus increasing the propensity to metastasise. HNSCC represents the sixth most frequent malignancy worldwide. These neoplasms, which arise from the mucous membranes of the various anatomical subsites of the upper aero-digestive tract, are heterogeneous in terms of aetiology and clinico-pathologic features. With current treatments, only about 50% of HNSCC patients survive beyond 5-years. Therefore, there is the pressing need to dissect NHSCC heterogeneity to inform treatment choices. In particular, reliable biomarkers of predictive and prognostic value are eagerly needed. This review describes the current state of the art and bio-pathological meaning of glycosylation signatures associated with HNSCC and explores the possible role of tumour specific glycoproteins as potential biomarkers and attractive therapeutic targets. We have also compiled data relating to altered glycosylation and the nature of glycoproteins as tools for the identification of circulating tumour cells (CTCs) in the new era of liquid biopsy.

Enumeration and molecular characterization of circulating tumor cells as an innovative tool for companion diagnostics in breast cancer

INTRODUCTION

Circulating tumor cells (CTC) and more recently, CTC clusters are implicated as a fundamental mechanism by which tumor cells break away from the primary site and travel to distant sites. Enumeration of CTC and CTC clusters represents a new approach to prognosis, prediction, and response to therapy in patients with early and metastatic breast cancer. Several recent studies have shown the predictive importance of monitoring CTCs levels in progression-free and overall survival in breast cancer patients. This review will focus on CTC enumeration and characterization in breast cancers.

AREAS COVERED

We will provide a historical perspective and clinical background of CTC detection in peripheral blood. The current methodologies for studying CTCs and newer technologies for CTC detection will be reviewed together with the current state of the art of CTCs as a biomarker in risk stratification and prognostication in breast cancers.

EXPERT OPINION

Currently, there is an FDA approved CTC assessment method for clinical use. While CTC enumeration, is a marker for prognostication and survival, molecular characterization of CTC, may be more accurate in monitoring response to treatment due to tumor heterogeneity rather than the tumor phenotype at the primary or metastatic sites.

A liquid biopsy-guided drug release system for cancer theranostics: integrating rapid circulating tumor cell detection and precision tumor therapy

Theranostics combining precision diagnosis and concurrent therapy has attracted significant attention as a promising strategy against life-threatening cancer. Liquid biopsy provides a real-time assessment of cancer by the analysis of tumor biomarkers, among which circulating tumor cells (CTCs) have been widely used to monitor disease progression and therapeutic response. In this study, a liquid biopsy-guided drug release system (LBDR system) integrating cancer diagnostic and therapeutic functions on a magnetically controlled microfluidic platform is presented. Two kinds of magnetic nanospheres (MNs), recognition MNs and drug-loaded MNs, are loaded onto the microfluidic chip to integrate the rapid detection of CTCs and controlled drug release. When CTCs bind to aptamers on the recognition MNs, complementary strands (cDNAs) hybridized with the aptamers are released and then conjugated with drug-loaded MNs to further trigger the release of anti-cancer drugs. The amount of drug released is controlled according to the number of detected CTCs, which can provide effective treatment for individual patients according to the diagnostic results. This LBDR system provides a novel strategy for cancer therapy and may facilitate the development of personalized cancer therapy.

Cell-Free DNA in the Liquid Biopsy Context: Role and Differences Between ctDNA and CTC Marker in Cancer Management

Liquid biopsy is a new diagnostic concept to investigate the molecular features of solid tumors by blood, saliva, urine, and any other body fluids which show a source of potential biomarkers. In cancer patients, it is a simple and less invasive mean, representing a sustainable alternative to interrogate all tumor cells longitudinally, quantifying and characterizing the biological materials (DNAs, RNAs, proteins) which originate from cancer tissues. Circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) analysis from a simple blood draw received enormous attention for the related clinical research results. A rich scientific literature demonstrates that liquid biopsy is a valid instrument to assess the tumor biomarkers in real time and profile the cancer genotype in diagnostic and prognostic field, as well to quantify minimal residual disease, during patient follow-up. This could be a breakthrough for a companion diagnostic and personalized medicine. Liquid biopsy needs further implementation in the methodological aspects as well as cost-based assessment. The number of new molecular diagnostic assays increases day by day, but the standards for their adoption and clinical validation are still to be achieved.

The Isolation and Analysis of Circulating Tumor Cells

Circulating tumor cells (CTCs), with their close association with cancer metastasis, the most aggressive feature of solid tumors, represent an important aspect of "liquid biopsy," which provides minimally- or noninvasive approaches for cancer detection and disease status monitoring. CTC analysis has shown the potential clinical applications in several cancer types and has been approved by FDA for clinical use in advanced breast, prostate, and colorectal cancer prognosis. In this chapter, we describe a CTC isolation method using a cell size and deformability-based system, Parsortix, and the immunofluorescence staining method to detect CTCs with both epithelial and mesenchymal features. We also describe a repeated fluorescence in situ hybridization (FISH) approach to detect alterations of multiple genomic regions on the same CTCs after immunofluorescence analysis. This approach allows the study of CTCs as a biomarker for cancer detection, prognosis, and therapeutic response monitoring, as well as the study of the heterogeneity of CTCs and cancers.

Nitric oxide is cytoprotective to breast cancer spheroids vulnerable to estrogen-induced apoptosis

Estrogen-induced apoptosis has become a successful treatment for postmenopausal metastatic, estrogen receptor-positive breast cancer. Nitric oxide involvement in the response to this endocrine treatment and its influence upon estrogen receptor-positive breast cancer progression is still unclear. Nitric oxide impact on the MCF7 breast cancer line, before and after estrogen-induced apoptosis, was investigated in 3D culture systems using unique live-cell imaging methodologies. Spheroids were established from MCF7 cells vulnerable to estrogen-induced apoptosis, before and after exposure to estrogen. Spheroids derived from estrogen-treated cells exhibited extensive apoptosis levels with downregulation of estrogen receptor expression, low proliferation rate and reduced metabolic activity, unlike spheroids derived from non-treated cells. In addition to basic phenotypic differences, these two cell cluster types are diverse in their reactions to exogenous nitric oxide. A dual effect of nitric oxide was observed in the breast cancer phenotype sensitive to estrogen-induced apoptosis. Nitric oxide, at the nanomolar level, induced cell proliferation, high metabolic activity, downregulation of estrogen receptor and enhanced collective invasion, contributing to a more aggressive phenotype. Following hormone supplementation, breast cancer 3D clusters were rescued from estrogen-induced apoptosis by these low nitric oxide-donor concentrations, since nitric oxide attenuates cell death levels, upregulates survivin expression and increases metabolic activity. Higher nitric oxide concentrations (100nM) inhibited cell growth, metabolism and promoted apoptosis. These results suggest that nitric oxide, in nanomolar concentrations, may inhibit estrogen-induced apoptosis, playing a major role in hormonal therapy. Inhibiting nitric oxide activity may benefit breast cancer patients and ultimately reduce tumor recurrence.

Tumor Heterogeneity in Breast Cancer

Breast cancer is a heterogeneous disease and differs greatly among different patients (intertumor heterogeneity) and even within each individual tumor (intratumor heterogeneity). Clinical and morphologic intertumor heterogeneity is reflected by staging systems and histopathologic classification of breast cancer. Heterogeneity in the expression of established prognostic and predictive biomarkers, hormone receptors, and human epidermal growth factor receptor 2 oncoprotein is the basis for targeted treatment. Molecular classifications are indicators of genetic tumor heterogeneity, which is probed with multigene assays and can lead to improved stratification into low- and high-risk groups for personalized therapy. Intratumor heterogeneity occurs at the morphologic, genomic, transcriptomic, and proteomic levels, creating diagnostic and therapeutic challenges. Understanding the molecular and cellular mechanisms of tumor heterogeneity that are relevant to the development of treatment resistance is a major area of research. Despite the improved knowledge of the complex genetic and phenotypic features underpinning tumor heterogeneity, there has been only limited advancement in diagnostic, prognostic, or predictive strategies for breast cancer. The current guidelines for reporting of biomarkers aim to maximize patient eligibility for targeted therapy, but do not take into account intratumor heterogeneity. The molecular classification of breast cancer is not implemented in routine clinical practice. Additional studies and in-depth analysis are required to understand the clinical significance of rapidly accumulating data. This review highlights inter- and intratumor heterogeneity of breast carcinoma with special emphasis on pathologic findings, and provides insights into the clinical significance of molecular and cellular mechanisms of heterogeneity.

Efficient leukocyte depletion by a novel microfluidic platform enables the molecular detection and characterization of circulating tumor cells

RT-qPCR is a highly sensitive approach to detect rare transcripts, as derived from circulating tumor cells (CTCs) in the blood of cancer patients. However, the presence of unwanted leukocytes often leads to false positive results. Here, we evaluated whether the micro-fluidic Parsortix™ technology is appropriate to remove these leukocytes and thereby finally to improve the overall approach.

In this study, we established a workflow including the micro-fluidic Parsortix™ technology for the molecular detection of CTC related transcripts. Background levels of EpCAM, PPIC, TUSC3, and MAL2 were efficiently removed due to an up to 10⁶-fold depletion of leukocytes. The presence of these gene markers was observed in Parsortix™-enriched blood samples from patients with primary and recurrent gynecological cancer (32% and 14%), as well as in 86% of the metastatic breast cancer samples, at a very high specificity. In the ovarian cancer samples, PPIC was the most prominent gene marker, contributing to all positive cases and at least to 70% of the positive cases after pre-amplification of the respective target genes. Expanding the analytical panel up to 29 gene markers further increased the positivity rate (primary gynecological cancer: 95%, recurrent gynecological cancer: 100%, metastatic breast cancer: 92%).

The established workflow strongly improved the overall molecular analysis of the target cells by the efficient removal of contaminating cells, and, thereby offers great promise for the molecular characterization of CTCs.

Circulating Tumor Cells as Cancer Biomarkers in the Clinic

It is believed that the development of metastatic cancer requires the presence of circulating tumor cells (CTCs) , which are found in a patient's circulation as rare abnormal cells comingled with billions of the normal red and white blood cells. The systems developed for detection of CTCs have brought progress to cancer treatment. The molecular characterization of CTCs can aid in the development of new drugs, and their presence during treatment can help clinicians determine the prognosis of the patient. Studies have been carried out in patients early in the disease course, with only primary tumors, and the role of CTCs in prognosis seems to be as important as it is in patients with metastatic disease. The published studies on CTCs have focused on their prognostic significance, their utility in real-time monitoring of therapies, the identification of therapeutic and resistance targets, and understanding the process of metastasis . The analysis of CTCs during the early stages, as a "liquid biopsy," helps to monitor patients at different points in the disease course, including minimal residual disease, providing valuable information about the very early assessment of treatment effectiveness. Finally, CTCs can be used to screen patients with family histories of cancer or with diseases that can lead to the development of cancer. With standard protocols, this easily obtained and practical tool can be used to prevent the growth and spread of cancer. In this chapter, we review some important aspects of CTCs , surveying the disease aspects where these cells have been investigated.

Mathematical models of cell phenotype regulation and reprogramming: Make cancer cells sensitive again!

A cell's phenotype is the observable actualization of complex interactions between its genome, epigenome, and local environment. While traditional views in cancer have held that cellular and tumor phenotypes are largely functions of genomic instability, increasing attention has recently been given to epigenetic and microenvironmental influences. Such non-genetic factors allow cancer cells to experience intrinsic diversity and plasticity, and at the tumor level can result in phenotypic heterogeneity and treatment evasion. In 2006, Takahashi and Yamanaka exploited the epigenome's plasticity by "reprogramming" differentiated cells into a pluripotent state by inducing expression of a cocktail of four transcription factors. Recent advances in cancer biology have shown not only that cellular reprogramming is possible for malignant cells, but it may provide a foundation for future therapies. Nevertheless, cell reprogramming experiments are frequently plagued by low efficiency, activation of aberrant transcriptional programs, instability, and often rely on expertise gathered from systems which may not translate directly to cancer. Here, we review a theoretical framework tracing back to Waddington's epigenetic landscape which may be used to derive quantitative and qualitative understanding of cellular reprogramming. Implications for tumor heterogeneity, evolution and adaptation are discussed in the context of designing new treatments to re-sensitize recalcitrant tumors. This article is part of a Special Issue entitled: Evolutionary principles - heterogeneity in cancer?, edited by Dr. Robert A. Gatenby.

Tumour Heterogeneity: The Key Advantages of Single-Cell Analysis

Tumour heterogeneity refers to the fact that different tumour cells can show distinct morphological and phenotypic profiles, including cellular morphology, gene expression, metabolism, motility, proliferation and metastatic potential. This phenomenon occurs both between tumours (inter-tumour heterogeneity) and within tumours (intra-tumour heterogeneity), and it is caused by genetic and non-genetic factors. The heterogeneity of cancer cells introduces significant challenges in using molecular prognostic markers as well as for classifying patients that might benefit from specific therapies. Thus, research efforts for characterizing heterogeneity would be useful for a better understanding of the causes and progression of disease. It has been suggested that the study of heterogeneity within Circulating Tumour Cells (CTCs) could also reflect the full spectrum of mutations of the disease more accurately than a single biopsy of a primary or metastatic tumour. In previous years, many high throughput methodologies have raised for the study of heterogeneity at different levels (i.e., RNA, DNA, protein and epigenetic events). The aim of the current review is to stress clinical implications of tumour heterogeneity, as well as current available methodologies for their study, paying specific attention to those able to assess heterogeneity at the single cell level.

Dual-patterned immunofiltration (DIF) device for the rapid efficient negative selection of heterogeneous circulating tumor cells

The analysis of circulating tumor cells (CTCs) is an emerging field for estimating the metastatic relapse and tumor burden of cancer patients. However, the isolation of CTCs is still challenging due to their ambiguity, rarity, and heterogeneity. Here, we present an anti-CD45 antibody based dual-patterned immunofiltration (DIF) device for the enrichment of heterogeneous CTC subtypes by effective elimination of leukocytes. Our uniquely designed dual-patterned layers significantly enhance the binding chance between immuno-patterns and leukocytes due to the fluidic whirling and the increased binding sites, thus achieving superior negative selection in terms of high-throughput and high purity. From the experiments using lung cancer cells, 97.07 ± 2.79% of leukocytes were eliminated with less than 10% loss of cancerous cells at the flow rate of 1 mL h^-1. To verify the device as a potential diagnostic tool, CTCs were collected from 11 cancer patients' blood and an average of 283.3 CTC-like cells were identified while less than 1 CTC-like cells were found from healthy donors. The samples were also analyzed by immunohistochemistry and the reverse transcription polymerase chain reaction to identify their heterogeneous characteristics. These remarkable results demonstrate that the present device could help to understand the unknown properties or undiscovered roles of CTCs with a non-biased view.

Circulating Tumor Cells and Circulating Tumor DNA Provide New Insights into Pancreatic Cancer

Pancreatic cancer has a rather dismal prognosis mainly due to high malignance of tumor biology. Up to now, the relevant researches on pancreatic cancer lag behind seriously partly due to the obstacles for tissue biopsy, which handicaps the understanding of molecular and genetic features of pancreatic cancer. In the last two decades, liquid biopsy, including circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA), is promising to provide new insights into the biological and clinical characteristics of malignant tumors. Both CTCs and ctDNA provide an opportunity for studying tumor heterogeneity, drug resistance, and metastatic mechanism for pancreatic cancer. Furthermore, they can also play important roles in detecting early-stage tumors, providing prognostic information, monitoring tumor progression and guiding treatment regimens. In this review, we will introduce the latest findings on biological features and clinical applications of both CTCs and ctDNA in pancreatic cancer. In a word, CTCs and ctDNA are promising to promote precision medicine in pancreatic cancer.

Delivery of nucleic acids for cancer gene therapy: overcoming extra- and intra-cellular barriers

The therapeutic potential of cancer gene therapy has been limited by the difficulty of delivering genetic material to target sites. Various biological and molecular barriers exist which need to be overcome before effective nonviral delivery systems can be applied successfully in oncology. Herein, various barriers are described and strategies to circumvent such obstacles are discussed, considering both the extracellular and intracellular setting. Development of multifunctional delivery systems holds much promise for the progression of gene delivery, and a growing body of evidence supports this approach involving rational design of vectors, with a unique molecular architecture. In addition, the potential application of composite gene delivery platforms is highlighted which may provide an alternative delivery strategy to traditional systemic administration.

Circulating Tumor Cells

Circulating Tumor Cells (CTC) are shed from primary or secondary tumors. Prior studies have demonstrated that enumeration of CTC is a robust independent prognostic factor of progression free and overall survival in patients with early and metastatic breast cancer. CTC, as well as other circulating tumor markers, have the appealing advantages over tissue biopsy of (1) ease of collection, (2) serial evaluation, and (3) interrogation of the entire tumor burden instead of just a limited part of the tumor. Advances have been recently made in phenotyping and genotyping of CTC, which should provide insights into the predictive role of CTC for sensitivity or resistance to therapies. In addition, CTC phenotypic marker changes during the course of treatment may serve as pharmacodynamic monitoring tools. Therefore, CTC may be considered "liquid biopsies," providing prognostic and predictive clinical information as well as additional understanding of tumor heterogeneity.

Prognostic Impact of Modulators of G proteins in Circulating Tumor Cells from Patients with Metastatic Colorectal Cancer

The consequence of a loss of balance between G-protein activation and deactivation in cancers has been interrogated by studying infrequently occurring mutants of trimeric G-protein α-subunits and GPCRs. Prior studies on members of a newly identified family of non-receptor guanine nucleotide exchange factors (GEFs), GIV/Girdin, Daple, NUCB1 and NUCB2 have revealed that GPCR-independent hyperactivation of trimeric G proteins can fuel metastatic progression in a variety of cancers. Here we report that elevated expression of each GEF in circulating tumor cells (CTCs) isolated from the peripheral circulation of patients with metastatic colorectal cancer is associated with a shorter progression-free survival (PFS). The GEFs were stronger prognostic markers than two other markers of cancer progression, S100A4 and MACC1, and clustering of all GEFs together improved the prognostic accuracy of the individual family members; PFS was significantly lower in the high-GEFs versus the low-GEFs groups [H.R = 5, 20 (95% CI; 2,15–12,57)]. Because nucleotide exchange is the rate-limiting step in cyclical activation of G-proteins, the poor prognosis conferred by these GEFs in CTCs implies that hyperactivation of G-protein signaling by these GEFs is an important event during metastatic progression, and may be more frequently encountered than mutations in G-proteins and/or GPCRs.

Enhanced and Differential Capture of Circulating Tumor Cells from Lung Cancer Patients by Microfluidic Assays Using Aptamer Cocktail

Collecting circulating tumor cells (CTCs) shed from solid tumor through a minimally invasive approach provides an opportunity to solve a long-standing oncology problem, the real-time monitoring of tumor state and analysis of tumor heterogeneity. However, efficient capture and detection of CTCs with diverse phenotypes is still challenging. In this work, a microfluidic assay is developed using the rationally-designed aptamer cocktails with synergistic effect. Enhanced and differential capture of CTCs for nonsmall cell lung cancer (NSCLC) patients is achieved. It is also demonstrated that the overall consideration of CTC counts obtained by multiple aptamer combinations can provide more comprehensive information in treatment monitoring.

Harnessing Pandemonium: The Clinical Implications of Tumor Heterogeneity in Ovarian Cancer

Heterogeneity has emerged as a key feature of ovarian cancer between different ovarian cancer subtypes; within single ovarian cancer subtypes; and within individual patient tumors. At the genomic level, with the advent of ultra-deep sequencing technologies alongside RNA-Seq, epigenomics, and proteomics, the complexity surrounding heterogeneity has deepened. Here, we summarize the emerging understanding of heterogeneity in cancer as a whole and the key discoveries in this area relating to ovarian cancer. We explore the therapeutic limitations and possibilities posed by heterogeneity and how these will influence the future of ovarian cancer treatment and research.

Retracing Circulating Tumour Cells for Biomarker Characterization after Enumeration

Background

Retracing and biomarker characterization of individual circulating tumour cells (CTCs) may potentially contribute to personalized metastatic cancer therapy. This is relevant when a biopsy of the metastasis is complicated or impossible to acquire.

Methods

A novel disc format was used to map and retrace individual CTCs from breast-cancer patients and nucleated cells from healthy blood donors using the CytoTrack platform. For proof of the retracing concept, CTC HER2 characterization by immunofluorescence was tested.

Results

CTCs were detected and enumerated in three of four blood samples from breast-cancer patients and the locations of each individual CTCs were mapped on the discs. Nucleated cells were retraced on seven discs with 96.6%±8.5% recovery on five fields of view on each disc. Shifting of field of view for retracing was measured to 4-29 μm. In a blood sample from a HER2-positive breast-cancer patient, CTC enumeration and mapping was followed by HER2 characterization and retracing to demonstrate downstream immunofluorescence analysis of the CTC.

Conclusion

Mapping and retracing of CTCs enables downstream analysis of individual CTCs for existing and future cancer genotypic and phenotypic biomarkers. Future studies will uncover this potential of the novel retracing technology.

Autologous tumor lysate/Bacillus Calmette-Guérin immunotherapy as an adjuvant to conventional breast cancer therapy

Introduction

Autologous tumor cell vaccines rely on the concept of preserving an individual’s own tumorigenic makeup, expressing its unique set of tumor-associated antigens as well as antigenic elements from the surrounding stroma. These autologous tumor characteristics are usually presented with an immune adjuvant in the hopes of enhancing an immune response.

Methods

The autologous vaccine we used was composed of tumor cells combined with BCG and formalin. Animal safety and toxicity were evaluated using mice tumors for the immunotherapy. A small number of patients with advanced stage breast cancer were recruited for an uncontrolled study, using the vaccine solely or combined with chemotherapy/radiotherapy.

Results

The immunotherapy had shown to be safe in mice and humans. Upon a 5-year follow-up, the survival rate was 60 % for the combined treatment.

Conclusions

The data suggest that the combined treatment could be a feasible and safe therapeutic strategy. However, further controlled studies should be conducted.

Stochastic particle barcoding for single-cell tracking and multiparametric analysis

This study presents stochastic particle barcoding (SPB), a method for tracking cell identity across bioanalytical platforms. In this approach, single cells or small collections of cells are co-encapsulated within an enzymatically-degradable hydrogel block along with a random collection of fluorescent beads, whose number, color, and position encode the identity of the cell, enabling samples to be transferred in bulk between single-cell assay platforms without losing the identity of individual cells. The application of SPB is demonstrated for transferring cells from a subnanoliter protein secretion/phenotyping array platform into a microtiter plate, with re-identification accuracies in the plate assay of 96±2%. Encapsulated cells are recovered by digesting the hydrogel, allowing subsequent genotyping and phenotyping of cell lysates. Finally, a model scaling is developed to illustrate how different parameters affect the accuracy of SPB and to motivate scaling of the method to thousands of unique blocks.

Metastasis dormancy in estrogen receptor-positive breast cancer

About 20% to 40% of patients with breast cancer eventually develop recurrences in distant organs, which are often not detected until years to decades after the primary tumor diagnosis. This phenomenon is especially pronounced in estrogen receptor-positive (ER(+)) breast cancer, suggesting that ER(+) cancer cells may stay dormant for a protracted period of time, despite adjuvant therapies. Multiple mechanisms have been proposed to explain how cancer cells survive and remain in dormancy, and how they become reactivated and exit dormancy. These mechanisms include angiogenic switch, immunosurveillance, and interaction with extracellular matrix and stromal cells. How to eradicate or suppress these dormant cancer cells remains a major clinical issue because of the lack of knowledge about the biologic and clinical nature of these cells. Herein, we review the clinical manifestation of metastasis dormancy in ER(+) tumors, the current biologic insights regarding tumor dormancy obtained from various experimental models, and the clinical challenges to predict, detect, and treat dormant metastases. We also discuss future research directions toward a better understanding of the biologic mechanisms and clinical management of ER(+) dormant metastasis.

Two-stage microfluidic chip for selective isolation of circulating tumor cells (CTCs)

Over the past few decades, circulating tumor cells (CTCs) have been studied as a means of overcoming cancer. However, the rarity and heterogeneity of CTCs have been the most significant hurdles in CTC research. Many techniques for CTC isolation have been developed and can be classified into positive enrichment (i.e., specifically isolating target cells using cell size, surface protein expression, and so on) and negative enrichment (i.e., specifically eluting non-target cells). Positive enrichment methods lead to high purity, but could be biased by their selection criteria, while the negative enrichment methods have relatively low purity, but can isolate heterogeneous CTCs. To compensate for the known disadvantages of the positive and negative enrichments, in this study we introduced a two-stage microfluidic chip. The first stage involves a microfluidic magnetic activated cell sorting (μ-MACS) chip to elute white blood cells (WBCs). The second stage involves a geometrically activated surface interaction (GASI) chip for the selective isolation of CTCs. We observed up to 763-fold enrichment in cancer cells spiked into 5 mL of blood sample using the μ-MACS chip at 400 μL/min flow rate. Cancer cells were successfully separated with separation efficiencies ranging from 10.19% to 22.91% based on their EpCAM or HER2 surface protein expression using the GASI chip at a 100 μL/min flow rate. Our two-stage microfluidic chips not only isolated CTCs from blood cells, but also classified heterogeneous CTCs based on their characteristics. Therefore, our chips can contribute to research on CTC heterogeneity of CTCs, and, by extension, personalized cancer treatment.

[Circulating tumor cells: cornerstone of personalized medicine]

Cancer treatment has evolved toward personalized medicine. It is mandatory for clinicians to ascertain tumor biological features in order to optimize patients' treatment. Identification and characterization of circulating tumor cells demonstrated a prognostic value in many solid tumors. Here, we describe the main technologies for identification and characterization of circulating tumor cells and their clinical application in gynecologic and breast cancers.

The challenge of intratumour heterogeneity in precision medicine

Cells within tumours have diverse genomes and epigenomes and interact differentially with their surrounding microenvironment generating intratumour heterogeneity, which has critical implications for treating cancer patients. Understanding the cellular and microenvironment composition and characteristics in individual tumours is critical to stratify the patient population that is likely to benefit from specific treatment regimens. Here, we will review the current understanding of intratumour heterogeneity at the genomic, epigenomic and microenvironmental levels. We will also discuss the clinical implications and the challenges posed by intratumour heterogeneity and evaluate noninvasive methods such as circulating biomarkers to characterize the cellular diversity of tumours. Comprehensive assessment of the molecular features of patients based on tumour specimen characterization (including intratumour spatial and temporal variations), ancillary noninvasive methods (such as circulating biomarkers and molecular imaging approaches) and the correct design of clinical trials are required to guide administration of targeted therapy and to control therapeutic resistance. Finding the means to accurately determine and effectively control tumour heterogeneity and translate these achievements into patient benefit are major goals in modern oncology.