Co-Expression of Stem Cell and Epithelial Mesenchymal Transition Markers in Circulating Tumor Cells of Bladder Cancer Patients

Current biological implications and clinical relevance of metastatic circulating tumor cells

Metastatic disease and cancer recurrence are the primary causes of cancer-related deaths. Circulating tumor cells (CTCs) and disseminated tumor cells (DTCs) are the driving forces behind the spread of cancer cells. The emergence and development of liquid biopsy using rare CTCs as a minimally invasive strategy for early-stage tumor detection and improved tumor management is a promising advancement in recent years. However, before blood sample analysis and clinical translation, precise isolation of CTCs from patients' blood based on their biophysical properties, followed by molecular identification of CTCs using single-cell multi-omics technologies is necessary to understand tumor heterogeneity and provide effective diagnosis and monitoring of cancer progression. Additionally, understanding the origin, morphological variation, and interaction between CTCs and the primary and metastatic tumor niche, as well as and regulatory immune cells, will offer new insights into the development of CTC-based advanced tumor targeting in the future clinical trials.

Multi-omic features and clustering phenotypes of circulating tumor cells associated with metastasis and clinical outcomes

Metastasis is a lethal disease of cancer, spreading from primary tumors to the bloodstream as circulating tumor cells (CTCs), which disseminate to distant organs at low efficiency for secondary tumor regeneration, thereby contributing to unfavorable patient outcomes. The detection of dynamic CTC alterations can be indicative of cancer progression (residual cancer, aggressiveness, therapy resistance) or regression (therapy response), serving as biomarkers for diagnoses and prognoses. CTC heterogeneity is impacted by both intrinsic oncogenic changes and extrinsic microenvironmental factors (e.g. the immune system and circadian rhythm), altering the genomic/genetic, epigenomic/epigenetic, proteomic, post-translational, and metabolomic landscapes. In addition to homeostatic dynamics, regenerative stemness, and metabolic plasticity, a newly discovered feature of CTCs that influences metastatic outcomes is its intercellular clustering. While the dogma suggests that CTCs play solo as single cells in the circulation, CTCs can orchestrate with other CTCs or white blood cells to form homotypic or heterotypic multi-cellular clusters, with 20-100 times enhanced metastatic potential than single CTCs. CTC clusters promote cell survival and stemness through DNA hypomethylation and signaling pathways activated by clustering-driving proteins (CD44, CD81, ICAM1, Podocalyxin, etc). Heterotypic CTC clusters may protect CTCs from immune cell attacks if not being cleared by cytotoxic immune cells. This chapter mainly focused on CTC biology related to multi-omic features and metastatic outcomes. We speculate that CTCs could guide therapeutic targeting and be targeted specifically by anti-CTC therapeutics to reduce or eliminate cancer and cancer metastasis.

Metastases and treatment-resistant lineages in patient-derived cancer cells of colorectal cancer

Circulating tumor cells (CTCs) play an important role in metastasis and recurrence. However, which cells comprise the complex tumor lineages in recurrence and are key in metastasis are unknown in colorectal cancer (CRC). CRC with high expression of POU5F1 has a poor prognosis with a high incidence of liver metastatic recurrence. We aim to reveal the key cells promoting metastasis and identify treatment-resistant lineages with established EGFP-expressing organoids in two-dimensional culture (2DOs) under the POU5F1 promotor. POU5F1-expressing cells are highly present in relapsed clinical patients' blood as CTCs. Sorted POU5F1-expressing cells from 2DOs have cancer stem cell abilities and abundantly form liver metastases in vivo. Single-cell RNA sequencing of 2DOs identifies heterogeneous populations derived from POU5F1-expressing cells and the Wnt signaling pathway is enriched in POU5F1-expressing cells. Characteristic high expression of CTLA4 is observed in POU5F1-expressing cells and immunocytochemistry confirms the co-expression of POU5F1 and CTLA4. Demethylation in some CpG islands at the transcriptional start sites of POU5F1 and CTLA4 is observed. The Wnt/β-catenin pathway inhibitor, XAV939, prevents the adhesion and survival of POU5F1-expressing cells in vitro. Early administration of XAV939 also completely inhibits liver metastasis induced by POU5F1-positive cells.

OCT4‑positive circulating tumor cells may predict a poor prognosis in patients with metastatic castration‑resistant prostate cancer treated with abiraterone plus prednisone therapy

Octamer-binding transcription factor 4 (OCT4) and circulating tumor cells (CTCs) are key factors associated with tumor metastasis and drug resistance in cancer. The present prospective study aimed to investigate the prevalence of OCT4-positive (OCT4+) CTCs and the potential association with the clinical features and survival of patients with metastatic castration-resistant prostate cancer (mCRPC) treated with abiraterone + prednisone. In total, 70 patients with mCRPC treated with abiraterone + prednisone were enrolled in the present study and peripheral blood samples were collected prior to treatment initiation to determine CTC count via a Canpatrol system. RNA in situ hybridization was performed for OCT4+ CTC quantification. Lactate dehydrogenase (LDH) was detected by automatic biochemical analyzer (AU54000, OLYMPUS). Results demonstrated that 34 (48.6%), 21 (30.0%) and 15 (21.4%) patients harbored OCT4+ (CTC+/OCT4+) or OCT4-negative CTCs (CTC+/OCT4-) or were CTC-negative (CTC-), respectively. Notably, CTC+/OCT4+ occurrence was associated with visceral metastasis and high levels of LDH. In addition, radiographic progression-free survival [rPFS; median, 15.0, 95% confidence interval (CI), 9.6-20.4 vs. not reached vs. median, 29.5, 95% CI, 18.6-40.4 months; P=0.001] and overall survival (OS) were significantly decreased (median, 27.3, 95% CI, 20.1-34.5 vs. not reached vs. not reached; P=0.016) in CTC+/OCT4+ compared with CTC+/OCT4- and CTC- patients. Subsequently, the adjustment was performed by multivariate Cox regression models, which revealed that CTC+/OCT4+ (vs. CTC+/OCT4- or CTC-) was independently associated with decreased rPFS [hazard ratio (HR), 3.833; P<0.001] and OS (HR, 3.938; P=0.008). In conclusion, OCT4+ CTCs were highly prevalent in patients with mCRPC and associated with visceral metastasis and increased levels of LDH. Thus, the presence of OCT4+ CTCs may serve as an independent prognostic factor for patients with mCRPC treated with abiraterone + prednisone.

Cancer stem cells: an insight into the development of metastatic tumors and therapy resistance

The term "cancer stem cells" (CSCs) refers to cancer cells that exhibit traits parallel to normal stem cells, namely the potential to give rise to every type of cell identified in a tumor microenvironment. It has been found that CSCs usually develops from other neoplastic cells or non-cancerous somatic cells by acquiring stemness and malignant characteristics through particular genetic modifications. A trivial number of CSCs, identified in solid and liquid cancer, can give rise to an entire tumor population with aggressive anticancer drug resistance, metastasis, and invasiveness. Besides, cancer stem cells manipulate their intrinsic and extrinsic features, regulate the metabolic pattern of the cell, adjust efflux-influx efficiency, modulate different signaling pathways, block apoptotic signals, and cause genetic and epigenetic alterations to retain their pluripotency and ability of self-renewal. Notably, to keep the cancer stem cells' ability to become malignant cells, mesenchymal stem cells, tumor-associated fibroblasts, immune cells, etc., interact with one another. Furthermore, CSCs are characterized by the expression of particular molecular markers that carry significant diagnostic and prognostic significance. Because of this, scientific research on CSCs is becoming increasingly imperative, intending to understand the traits and behavior of cancer stem cells and create more potent anticancer therapeutics to fight cancer at the CSC level. In this review, we aimed to elucidate the critical role of CSCs in the onset and spread of cancer and the characteristics of CSCs that promote severe resistance to targeted therapy.

Blood-based liquid biopsy: insights into early detection, prediction, and treatment monitoring of bladder cancer

Bladder cancer (BC) is a clinical challenge worldwide with late clinical presentation, poor prognosis, and low survival rates. Traditional cystoscopy and tissue biopsy are routine methods for the diagnosis, prognosis, and monitoring of BC. However, due to the heterogeneity and limitations of tumors, such as aggressiveness, high cost, and limited applicability of longitudinal surveillance, the identification of tumor markers has attracted significant attention in BC. Over the past decade, liquid biopsies (e.g., blood) have proven to be highly efficient methods for the discovery of BC biomarkers. This noninvasive sampling method is used to analyze unique tumor components released into the peripheral circulation and allows serial sampling and longitudinal monitoring of tumor progression. Several liquid biopsy biomarkers are being extensively studied and have shown promising results in clinical applications of BC, including early detection, detection of microscopic residual disease, prediction of recurrence, and response to therapy. Therefore, in this review, we aim to provide an update on various novel blood-based liquid biopsy markers and review the advantages and current limitations of liquid biopsy in BC therapy. The role of blood-based circulating tumor cells, circulating tumor DNA, cell-free RNA, exosomes, metabolomics, and proteomics in diagnosis, prognosis, and treatment monitoring, and their applicability to the personalized management of BC, are highlighted.

Application of Circulating Tumor Cells and Circulating Free DNA from Peripheral Blood in the Prognosis of Advanced Gastric Cancer

Objective

To explore the application value of circulating tumor cells (CTCs) and circulating free DNA (cfDNA) from peripheral blood in the prognosis of advanced gastric cancer (AGC). Here, we measured CTCs and cfDNA quantity for predicting the outcome of patients. Patients and Methods. Forty-five patients with advanced gastric cancer who underwent neoadjuvant chemotherapy and surgical treatment were enrolled in this study. All patients received neoadjuvant chemotherapy with paclitaxel + S-1 + oxaliplatin (PSOX) regimen, and CTCs and cfDNA of the peripheral blood were detected before and after neoadjuvant therapy. Relationships between the number/type of CTC or cfDNA and the efficacy of neoadjuvant chemotherapy were analyzed.

Results

Among 45 patients, 43 (95.6%) were positive, and the positive rate of mesenchymal CTC was increased with the increase in the T stage. The proportion of mesenchymal CTC was positively correlated with the N stage (P < 0.05), and the larger N stage will have the higher proportion of mesenchymal CTC. Patients with a small number of mesenchymal CTC before neoadjuvant chemotherapy were more likely to achieve partial response (PR) with neoadjuvant therapy. Patients with positive CA-199 were more likely to achieve PR with neoadjuvant therapy (P < 0.05). Patients in the PR group were more likely to have decreased/unchanged cfDNA concentration after neoadjuvant therapy (P=0.119). After neoadjuvant therapy (before surgery), the cfDNA concentration was higher and the efficacy of neoadjuvant therapy (SD or PD) was lower (P=0.045).

Conclusions

Peripheral blood CTC, especially interstitial CTC and cfDNA, has a certain value in predicting the efficacy and prognosis of neoadjuvant chemotherapy in advanced gastric cancer.

Circulating tumor cells: biology and clinical significance

Circulating tumor cells (CTCs) are tumor cells that have sloughed off the primary tumor and extravasate into and circulate in the blood. Understanding of the metastatic cascade of CTCs has tremendous potential for the identification of targets against cancer metastasis. Detecting these very rare CTCs among the massive blood cells is challenging. However, emerging technologies for CTCs detection have profoundly contributed to deepening investigation into the biology of CTCs and have facilitated their clinical application. Current technologies for the detection of CTCs are summarized herein, together with their advantages and disadvantages. The detection of CTCs is usually dependent on molecular markers, with the epithelial cell adhesion molecule being the most widely used, although molecular markers vary between different types of cancer. Properties associated with epithelial-to-mesenchymal transition and stemness have been identified in CTCs, indicating their increased metastatic capacity. Only a small proportion of CTCs can survive and eventually initiate metastases, suggesting that an interaction and modulation between CTCs and the hostile blood microenvironment is essential for CTC metastasis. Single-cell sequencing of CTCs has been extensively investigated, and has enabled researchers to reveal the genome and transcriptome of CTCs. Herein, we also review the clinical applications of CTCs, especially for monitoring response to cancer treatment and in evaluating prognosis. Hence, CTCs have and will continue to contribute to providing significant insights into metastatic processes and will open new avenues for useful clinical applications.

Circular RNA circSETD3 hampers cell growth, migration, and stem cell properties in bladder cancer through sponging miR-641 to upregulate PTEN

Bladder cancer (BLCA) is a common malignant urothelial cancer in the world. Although circular RNAs (circRNAs) involve in regulating BLCA progression, the role of a novel circular RNA circSETD3 in regulating BLCA pathogenesis has not been studied. The expression of circSETD3, miR-641, PTEN mRNA in BLCA tissues and cell lines were measured using RT-qPCR. The gain-of-function experiments were performed in vitro and in vivo to detect the effects of circSETD3 on cell proliferation, migration, EMT, and stemness maintenance. Besides, rescue experiments were performed to demonstrate the regulatory mechanism of circSETD3/miR-641/PTEN in BLCA cell malignant phenotypes in vitro. CircSETD3 was remarkably downregulated in the cancerous clinical tissues and cell lines, in contrast with their normal counterparts, and circSETD3 tended to be deficient in BLCA patients with larger tumor size, advanced clinical stages, positive lymph metastasis and worse prognosis. In addition, circular isoforms of circSETD3 were more resistant to RNase R+ and actinomycetes D treatment compared to their linear isoforms, and circSETD3 mainly distributed in the cytoplasm of the BLCA cells. Further gain-of-function experiments showed that circSETD3 acted as a tumor suppressor to suppress BLCA cell proliferation, migration, EMT and stemness, and the underlying mechanisms had also been elucidated. Mechanistically, circSETD3 sponged miR-641 to upregulate PTEN, resulting in the blockage of BLCA progression. Our findings indicated that circSETD3 acted as a vital tumor suppressor in BLCA via regulating the miR-641/PTEN axis.

MicroRNAs and Stem-like Properties: The Complex Regulation Underlying Stemness Maintenance and Cancer Development

Embryonic stem cells (ESCs) have the extraordinary properties to indefinitely proliferate and self-renew in culture to produce different cell progeny through differentiation. This latter process recapitulates embryonic development and requires rounds of the epithelial-mesenchymal transition (EMT). EMT is characterized by the loss of the epithelial features and the acquisition of the typical phenotype of the mesenchymal cells. In pathological conditions, EMT can confer stemness or stem-like phenotypes, playing a role in the tumorigenic process. Cancer stem cells (CSCs) represent a subpopulation, found in the tumor tissues, with stem-like properties such as uncontrolled proliferation, self-renewal, and ability to differentiate into different cell types. ESCs and CSCs share numerous features (pluripotency, self-renewal, expression of stemness genes, and acquisition of epithelial-mesenchymal features), and most of them are under the control of microRNAs (miRNAs). These small molecules have relevant roles during both embryogenesis and cancer development. The aim of this review was to recapitulate molecular mechanisms shared by ESCs and CSCs, with a special focus on the recently identified classes of microRNAs (noncanonical miRNAs, mirtrons, isomiRs, and competitive endogenous miRNAs) and their complex functions during embryogenesis and cancer development.

Communication Between Epithelial-Mesenchymal Plasticity and Cancer Stem Cells: New Insights Into Cancer Progression

The epithelial–mesenchymal transition (EMT) is closely associated with the acquisition of aggressive traits by carcinoma cells and is considered responsible for metastasis, relapse, and chemoresistance. Molecular links between the EMT and cancer stem cells (CSCs) have indicated that EMT processes play important roles in the expression of CSC-like properties. It is generally thought that EMT-related transcription factors (EMT-TFs) need to be downregulated to confer an epithelial phenotype to mesenchymal cells and increase cell proliferation, thereby promoting metastasis formation. However, the genetic and epigenetic mechanisms that regulate EMT and CSC activation are contradictory. Emerging evidence suggests that EMT need not be a binary model and instead a hybrid epithelial/mesenchymal state. This dynamic process correlates with epithelial–mesenchymal plasticity, which indicates a contradictory role of EMT during cancer progression. Recent studies have linked the epithelial–mesenchymal plasticity and stem cell-like traits, providing new insights into the conflicting relationship between EMT and CSCs. In this review, we examine the current knowledge about the interplay between epithelial–mesenchymal plasticity and CSCs in cancer biology and evaluate the controversies and future perspectives. Understanding the biology of epithelial–mesenchymal plasticity and CSCs and their implications in therapeutic treatment may provide new opportunities for targeted intervention.

Cancer Stem Cells-Key Players in Tumor Relapse

Tumor relapse and treatment failure are unfortunately common events for cancer patients, thus often rendering cancer an uncurable disease. Cancer stem cells (CSCs) are a subset of cancer cells endowed with tumor-initiating and self-renewal capacity, as well as with high adaptive abilities. Altogether, these features contribute to CSC survival after one or multiple therapeutic approaches, thus leading to treatment failure and tumor progression/relapse. Thus, elucidating the molecular mechanisms associated with stemness-driven resistance is crucial for the development of more effective drugs and durable responses. This review will highlight the mechanisms exploited by CSCs to overcome different therapeutic strategies, from chemo- and radiotherapies to targeted therapies and immunotherapies, shedding light on their plasticity as an insidious trait responsible for their adaptation/escape. Finally, novel CSC-specific approaches will be described, providing evidence of their preclinical and clinical applications.