Roles of cell fusion, hybridization and polyploid cell formation in cancer metastasis

The microtubule targeting agent ST-401 triggers cell death in interphase and prevents the formation of polyploid giant cancer cells

Microtubule targeting agents (MTAs) are commonly prescribed to treat cancers and predominantly kill cancer cells in mitosis. Significantly, some MTA-treated cancer cells escape death in mitosis, exit mitosis and become malignant polyploid giant cancer cells (PGCC). Considering the low number of cancer cells undergoing mitosis in tumor tissues, killing them in interphase may represent a favored antitumor approach. We discovered that ST-401, a mild inhibitor of microtubule (MT) assembly, preferentially kills cancer cells in interphase as opposed to mitosis, a cell death mechanism that avoids the development of PGCC. Single cell RNA sequencing identified mRNA transcripts regulated by ST-401, including mRNAs involved in ribosome and mitochondrial functions. Accordingly, ST-401 induces a transient integrated stress response, reduces energy metabolism, and promotes mitochondria fission. This cell response may underly death in interphase and avoid the development of PGCC. Considering that ST-401 is a brain-penetrant MTA, we validated these results in glioblastoma cell lines and found that ST-401 also reduces energy metabolism and promotes mitochondria fission in GBM sensitive lines. Thus, brain-penetrant mild inhibitors of MT assembly, such as ST-401, that induce death in interphase through a previously unanticipated antitumor mechanism represent a potentially transformative new class of therapeutics for the treatment of GBM.

scRNAseq and High-Throughput Spatial Analysis of Tumor and Normal Microenvironment in Solid Tumors Reveal a Possible Origin of Circulating Tumor Hybrid Cells

Metastatic cancer is a leading cause of death in cancer patients worldwide. While circulating hybrid cells (CHCs) are implicated in metastatic spread, studies documenting their tissue origin remain sparse, with limited candidate approaches using one-two markers. Utilizing high-throughput single-cell and spatial transcriptomics, we identified tumor hybrid cells (THCs) co-expressing epithelial and macrophage markers and expressing a distinct transcriptome. Rarely, normal tissue showed these cells (NHCs), but their transcriptome was easily distinguishable from THCs. THCs with unique transcriptomes were observed in breast and colon cancers, suggesting this to be a generalizable phenomenon across cancer types. This study establishes a framework for HC identification in large datasets, providing compelling evidence for their tissue residence and offering comprehensive transcriptomic characterization. Furthermore, it sheds light on their differential function and identifies pathways that could explain their newly acquired invasive capabilities. THCs should be considered as potential therapeutic targets.

Obesity, bone marrow adiposity, and leukemia: Time to act

Obesity has taken the face of a pandemic with less direct concern among the general population and scientific community. However, obesity is considered a low-grade systemic inflammation that impacts multiple organs. Chronic inflammation is also associated with different solid and blood cancers. In addition, emerging evidence demonstrates that individuals with obesity are at higher risk of developing blood cancers and have poorer clinical outcomes than individuals in a normal weight range. The bone marrow is critical for hematopoiesis, lymphopoiesis, and myelopoiesis. Therefore, it is vital to understand the mechanisms by which obesity-associated changes in BM adiposity impact leukemia development. BM adipocytes are critical to maintain homeostasis via different means, including immune regulation. However, obesity increases BM adiposity and creates a pro-inflammatory environment to upregulate clonal hematopoiesis and a leukemia-supportive environment. Obesity further alters lymphopoiesis and myelopoiesis via different mechanisms, which dysregulate myeloid and lymphoid immune cell functions mentioned in the text under different sequentially discussed sections. The altered immune cell function during obesity alters hematological malignancies and leukemia susceptibility. Therefore, obesity-induced altered BM adiposity, immune cell generation, and function impact an individual's predisposition and severity of leukemia, which should be considered a critical factor in leukemia patients.

Cell fusion between tumor cells and macrophages promotes the metastasis of OSCC patient through the activation of the chemokine signaling pathway

BACKGROUND

Tumor metastasis is responsible for the high mortality rate of patients with oral squamous cell carcinoma (OSCC). Although many hypotheses have been proposed to elucidate the mechanism of tumor metastasis, the origin of the metastatic tumor cells remains unclear. In this study, we explored the role of cell fusion in the formation of OSCC metastatic tumor cells.

METHODS

Murine OSCC tumor cells and macrophages were fused in vitro, and the cell proliferation, migration, and phagocytosis abilities of hybrid cells and parental cells were compared. Subsequently, we compared the transcriptome differences between hybrid and parental cells.

RESULTS

Murine OSCC tumor cells and macrophages were successfully fused in vitro. The cytological and molecular experimental results revealed that OSCC tumor cells obtained a migration-related phenotype after fusion with macrophages, and the migration ability of hybrid cells was related to the activation of the "chemokine signal pathway".

CONCLUSION

After fusion with macrophages, the chemokine signaling pathway in OSCC tumor cells was activated, leading to metastasis.

Mitosis exit followed by death in interphase prevents the development of polyploid giant cancer cells

Microtubule targeting agents ( MTAs ) are commonly prescribed to treat cancers and predominantly kill cancer cells in mitosis. Significantly, some MTA-treated cancer cells can escape death in mitosis and exit mitosis, and become malignant polyploid giant cancer cells ( PGCC ). Considering the low number of malignant cells undergoing mitosis in tumor tissue, killing these cells in interphase may represent a favored antitumor approach. We discovered that ST-401, a mild inhibitor of microtubule assembly, preferentially kills cancer cells in interphase as opposed to mitosis, and avoids the development of PGCC. Single cell RNA sequencing identified mRNA transcripts regulated by ST-401, including mRNAs involved in ribosome and mitochondrial functions. Accordingly, ST-401 induces an integrated stress response and promotes mitochondria fission accompanied by a reduction in energy metabolism. This cell response may underly death in interphase and avoid the development of PGCC.

Why do certain cancer cells alter functionality and fuse?

Cancer cell fusion represents a rare event. However, the surviving cancer hybrid cells after a post-hybrid selection process (PHSP) can overgrow other cancer cells by exhibiting a proliferation advantage and/or expression of cancer stem-like properties. Addition of new tumor properties during hetero-fusion of cancer cells e.g. with mesenchymal stroma-/stem-like cells (MSC) contribute to enhanced tumor plasticity via acquisition of new/altered functionalities. This provides new avenues for tumor development and metastatic behavior. Consequently, the present review article will also address the question as to whether cancer cell fusion represents a general and possibly evolutionary-conserved program or rather a random process?

Intratumor Heterogeneity and Treatment Resistance of Solid Tumors with a Focus on Polyploid/Senescent Giant Cancer Cells (PGCCs)

Single cell biology has revealed that solid tumors and tumor-derived cell lines typically contain subpopulations of cancer cells that are readily distinguishable from the bulk of cancer cells by virtue of their enormous size. Such cells with a highly enlarged nucleus, multiple nuclei, and/or multiple micronuclei are often referred to as polyploid giant cancer cells (PGCCs), and may exhibit features of senescence. PGCCs may enter a dormant phase (active sleep) after they are formed, but a subset remain viable, secrete growth promoting factors, and can give rise to therapy resistant and tumor repopulating progeny. Here we will briefly discuss the prevalence and prognostic value of PGCCs across different cancer types, the current understanding of the mechanisms of their formation and fate, and possible reasons why these tumor repopulating "monsters" continue to be ignored in most cancer therapy-related preclinical studies. In addition to PGCCs, other subpopulations of cancer cells within a solid tumor (such as oncogenic caspase 3-activated cancer cells and drug-tolerant persister cancer cells) can also contribute to therapy resistance and pose major challenges to the delivery of cancer therapy.

Cells in the polyaneuploid cancer cell (PACC) state have increased metastatic potential

Although metastasis is the leading cause of cancer deaths, it is quite rare at the cellular level. Only a rare subset of cancer cells (~ 1 in 1.5 billion) can complete the entire metastatic cascade: invasion, intravasation, survival in the circulation, extravasation, and colonization (i.e. are metastasis competent). We propose that cells engaging a Polyaneuploid Cancer Cell (PACC) phenotype are metastasis competent. Cells in the PACC state are enlarged, endocycling (i.e. non-dividing) cells with increased genomic content that form in response to stress. Single-cell tracking using time lapse microscopy reveals that PACC state cells have increased motility. Additionally, cells in the PACC state exhibit increased capacity for environment-sensing and directional migration in chemotactic environments, predicting successful invasion. Magnetic Twisting Cytometry and Atomic Force Microscopy reveal that cells in the PACC state display hyper-elastic properties like increased peripheral deformability and maintained peri-nuclear cortical integrity that predict successful intravasation and extravasation. Furthermore, four orthogonal methods reveal that cells in the PACC state have increased expression of vimentin, a hyper-elastic biomolecule known to modulate biomechanical properties and induce mesenchymal-like motility. Taken together, these data indicate that cells in the PACC state have increased metastatic potential and are worthy of further in vivo analysis.

Systemic Alterations of Cancer Cells and Their Boost by Polyploidization: Unicellular Attractor (UCA) Model

Using meta-analyses, we introduce a unicellular attractor (UCA) model integrating essential features of the ‘atavistic reversal’, ‘cancer attractor’, ‘somatic mutation’, ‘genome chaos’, and ‘tissue organization field’ theories. The ‘atavistic reversal’ theory is taken as a keystone. We propose a possible mechanism of this reversal, its refinement called ‘gradual atavism’, and evidence for the ‘serial atavism’ model. We showed the gradual core-to-periphery evolutionary growth of the human interactome resulting in the higher protein interaction density and global interactome centrality in the UC center. In addition, we revealed that UC genes are more actively expressed even in normal cells. The modeling of random walk along protein interaction trajectories demonstrated that random alterations in cellular networks, caused by genetic and epigenetic changes, can result in a further gradual activation of the UC center. These changes can be induced and accelerated by cellular stress that additionally activates UC genes (especially during cell proliferation), because the genes involved in cellular stress response and cell cycle are mostly of UC origin. The functional enrichment analysis showed that cancer cells demonstrate the hyperactivation of energetics and the suppression of multicellular genes involved in communication with the extracellular environment (especially immune surveillance). Collectively, these events can unleash selfish cell behavior aimed at survival at all means. All these changes are boosted by polyploidization. The UCA model may facilitate an understanding of oncogenesis and promote the development of therapeutic strategies.

Mechanisms of radioresistance and the underlying signaling pathways in colorectal cancer cells

Radiotherapy is one of the most common modalities for the treatment of a wide range of tumors, including colorectal cancer (CRC); however, radioresistance of cancer cells remains a major limitation for this treatment. Following radiotherapy, the activities of various cellular mechanisms and cell signaling pathways are altered, resulting in the development of radioresistance, which leads to therapeutic failure and poor prognosis in patients with cancer. Furthermore, even though several inhibitors have been developed to target tumor resistance, these molecules can induce side effects in nontumor cells due to low specificity and efficiency. However, the role of these mechanisms in CRC has not been extensively studied. This review discusses recent studies regarding the relationship between radioresistance and the alterations in a series of cellular mechanisms and cell signaling pathways that lead to therapeutic failure and tumor recurrence. Our review also presents recent advances in the in vitro/in vivo study models aimed at investigating the radioresistance mechanism in CRC. Furthermore, it provides a relevant biochemical basis in theory, which can be useful to improve radiotherapy sensitivity and prolong patient survival.

Fusion Cell Markers in Circulating Tumor Cells from Patients with High-Grade Ovarian Serous Carcinoma

Cancer is primarily a disease in which late diagnosis is linked to poor prognosis, and unfortunately, detection and management are still challenging. Circulating tumor cells (CTCs) are a potential resource to address this disease. Cell fusion, an event discovered recently in CTCs expressing carcinoma and leukocyte markers, occurs when ≥2 cells become a single entity (hybrid cell) after the merging of their plasma membranes. Cell fusion is still poorly understood despite continuous evaluations in in vitro/in vivo studies. Blood samples from 14 patients with high-grade serous ovarian cancer (A.C. Camargo Cancer Center, São Paulo, Brazil) were collected with the aim to analyze the CTCs/hybrid cells and their correlation to clinical outcome. The EDTA collected blood (6 mL) from patients was used to isolate/identify CTCs/hybrid cells by ISET. We used markers with possible correlation with the phenomenon of cell fusion, such as MC1-R, EpCAM and CD45, as well as CEN8 expression by CISH analysis. Samples were collected at three timepoints: baseline, after one month (first follow-up) and after three months (second follow-up) of treatment with olaparib (total sample = 38). Fourteen patients were included and in baseline and first follow-up all patients showed at least one CTC. We found expression of MC1-R, EpCAM and CD45 in cells (hybrid) in at least one of the collection moments. Membrane staining with CD45 was found in CTCs from the other cohort, from the other center, evaluated by the CellSearch^® system. The presence of circulating tumor microemboli (CTM) in the first follow-up was associated with a poor recurrence-free survival (RFS) (5.2 vs. 12.2 months; p = 0.005). The MC1-R expression in CTM in the first and second follow-ups was associated with a shorter RFS (p = 0.005). CEN8 expression in CTCs was also related to shorter RFS (p = 0.035). Our study identified a high prevalence of CTCs in ovarian cancer patients, as well as hybrid cells. Both cell subtypes demonstrate utility in prognosis and in the assessment of response to treatment. In addition, the expression of MC1-R and EpCAM in hybrid cells brings new perspectives as a possible marker for this phenomenon in ovarian cancer.

Circulating Endothelial Cells: A New Possible Marker of Endothelial Damage in Kawasaki Disease, Multisystem Inflammatory Syndrome in Children and Acute SARS-CoV-2 Infection

BACKGROUND

Kawasaki Disease (KD) and Multisystem Inflammatory Syndrome in Children (MIS-C) are pediatric diseases characterized by systemic inflammation and vascular injury, potentially leading to coronary artery lesions (CALs). Data on vascular injury occurring during acute COVID-19 (AC19) in children are still lacking. The aim of our study was to investigate endothelial injury in KD-, MIS-C- and AC19-dosing circulating endothelial cells (CECs).

METHODS

We conducted a multicenter prospective study. CECs were enumerated by CellSearch technology through the immunomagnetic capture of CD146-positive cells from whole blood.

RESULTS

We enrolled 9 KD, 20 MIS-C and 10 AC19. During the acute stage, the AC19 and KD patients had higher CECs levels than the MIS-C patients. From the acute to subacute phase, a significant CEC increase was observed in the KD patients, while a mild decrease was detected in the MIS-C patients. Cellular clusters/syncytia were more common in the KD patients. No correlation between CECs and CALs were found in the MIS-C patients. The incidence of CALs in the KD group was too low to investigate this correlation.

CONCLUSIONS

Our study suggests a possible role of CECs as biomarkers of systemic inflammation and endothelial dysfunction in KD and MIS-C and different mechanisms of vascular injury in these diseases. Further larger studies are needed.

Monocyte-Macrophage Lineage Cell Fusion

Cell fusion (fusogenesis) occurs in natural and pathological conditions in prokaryotes and eukaryotes. Cells of monocyte–macrophage lineage are highly fusogenic. They create syncytial multinucleated giant cells (MGCs) such as osteoclasts (OCs), MGCs associated with the areas of infection/inflammation, and foreign body-induced giant cells (FBGCs). The fusion of monocytes/macrophages with tumor cells may promote cancer metastasis. We describe types and examples of monocyte–macrophage lineage cell fusion and the role of actin-based structures in cell fusion.

Optimization study of plasmonic cell fusion

Artificial cell fusion often serves as a valuable tool for studying different applications in biology and medicine, including natural development, immune response, cancer metastasis and production of therapeutic molecules. Plasmonic cell fusion, a technique that uses specific cell labeling by gold nanoparticles and resonant femtosecond pulse irradiation for fusing neighboring cells, has been demonstrated useful for such applications, allowing high cell specificity and an overall low toxicity. Despite these advantages, the numerous experimental factors contributing to plasmonic fusion have often led to subpar fusion efficiencies, requiring repeated experiments and extensive calibration protocols for achieving optimal results. In this work we present a study that aims to improve the overall performance of plasmonic cell fusion in terms of fusion efficiency and cell viability. By varying the pulse fluence, nanoparticle concentration, incubation times, and culture handling protocols, we demonstrate up to 100% fusion of malignant epithelial cells across the entire irradiated area of the culture. We also show that some of the smaller cells may stay viable for up to several days. The results would allow plasmonic fusion to play a key role in numerous studies and applications that require specific, high-efficiency cell-cell fusion.

Generation of Cancer Stem/Initiating Cells by Cell-Cell Fusion

CS/ICs have raised great expectations in cancer research and therapy, as eradication of this key cancer cell type is expected to lead to a complete cure. Unfortunately, the biology of CS/ICs is rather complex, since no common CS/IC marker has yet been identified. Certain surface markers or ALDH1 expression can be used for detection, but some studies indicated that cancer cells exhibit a certain plasticity, so CS/ICs can also arise from non-CS/ICs. Another problem is intratumoral heterogeneity, from which it can be inferred that different CS/IC subclones must be present in the tumor. Cell–cell fusion between cancer cells and normal cells, such as macrophages and stem cells, has been associated with the generation of tumor hybrids that can exhibit novel properties, such as an enhanced metastatic capacity and even CS/IC properties. Moreover, cell–cell fusion is a complex process in which parental chromosomes are mixed and randomly distributed among daughter cells, resulting in multiple, unique tumor hybrids. These, if they have CS/IC properties, may contribute to the heterogeneity of the CS/IC pool. In this review, we will discuss whether cell–cell fusion could also lead to the origin of different CS/ICs that may expand the overall CS/IC pool in a primary tumor.

Hybrid/Atypical Forms of Circulating Tumor Cells: Current State of the Art

Cancer is one of the most common diseases worldwide, and its treatment is associated with many challenges such as drug and radioresistance and formation of metastases. These difficulties are due to tumor heterogeneity, which has many causes. One may be the cell fusion, a process that is relevant to both physiological (e.g., wound healing) and pathophysiological (cancer and viral infection) processes. This literature review aimed to summarize the existing data on the hybrid/atypical forms of circulating cancer cells and their role in tumor progression. For that, the bioinformatics search in universal databases, such as PubMed, NCBI, and Google Scholar was conducted by using the keywords “hybrid cancer cells”, “cancer cell fusion”, etc. In this review the latest information related to the hybrid tumor cells, theories of their genesis, characteristics of different variants with data from our own researches are presented. Many aspects of the hybrid cell research are still in their infancy. However, with the level of knowledge already accumulated, circulating hybrids such as CAML and CHC could be considered as promising biomarkers of cancerous tumors, and even more as a new approach to cancer treatment.

Polyploidy as a Fundamental Phenomenon in Evolution, Development, Adaptation and Diseases

DNA replication during cell proliferation is 'vertical' copying, which reproduces an initial amount of genetic information. Polyploidy, which results from whole-genome duplication, is a fundamental complement to vertical copying. Both organismal and cell polyploidy can emerge via premature cell cycle exit or via cell-cell fusion, the latter giving rise to polyploid hybrid organisms and epigenetic hybrids of somatic cells. Polyploidy-related increase in biological plasticity, adaptation, and stress resistance manifests in evolution, development, regeneration, aging, oncogenesis, and cardiovascular diseases. Despite the prevalence in nature and importance for medicine, agri- and aquaculture, biological processes and epigenetic mechanisms underlying these fundamental features largely remain unknown. The evolutionarily conserved features of polyploidy include activation of transcription, response to stress, DNA damage and hypoxia, and induction of programs of morphogenesis, unicellularity, and longevity, suggesting that these common features confer adaptive plasticity, viability, and stress resistance to polyploid cells and organisms. By increasing cell viability, polyploidization can provide survival under stressful conditions where diploid cells cannot survive. However, in somatic cells it occurs at the expense of specific function, thus promoting developmental programming of adult cardiovascular diseases and increasing the risk of cancer. Notably, genes arising via evolutionary polyploidization are heavily involved in cancer and other diseases. Ploidy-related changes of gene expression presumably originate from chromatin modifications and the derepression of bivalent genes. The provided evidence elucidates the role of polyploidy in evolution, development, aging, and carcinogenesis, and may contribute to the development of new strategies for promoting regeneration and preventing cardiovascular diseases and cancer.

Cell Fusion-Related Proteins and Signaling Pathways, and Their Roles in the Development and Progression of Cancer

Cell fusion is involved in many physiological and pathological processes, including gamete binding, and cancer development. The basic processes of cell fusion include membrane fusion, cytoplasmic mixing, and nuclear fusion. Cell fusion is regulated by different proteins and signaling pathways. Syncytin-1, syncytin-2, glial cell missing 1, galectin-1 and other proteins (annexins, myomaker, myomerger etc.) involved in cell fusion via the cyclic adenosine-dependent protein kinase A, mitogen-activated protein kinase, wingless/integrase-1, and c-Jun N-terminal kinase signaling pathways. In the progression of malignant tumors, cell fusion is essential during the organ-specific metastasis, epithelial-mesenchymal transformation, the formation of cancer stem cells (CSCs), cancer angiogenesis and cancer immunity. In addition, diploid cells can be induced to form polyploid giant cancer cells (PGCCs) via cell fusion under many kinds of stimuli, including cobalt chloride, chemotherapy, radiotherapy, and traditional Chinese medicine. PGCCs have CSC-like properties, and the daughter cells derived from PGCCs have a mesenchymal phenotype and exhibit strong migration, invasion, and proliferation abilities. Therefore, exploring the molecular mechanisms of cell fusion can enable us better understand the development of malignant tumors. In this review, the basic process of cell fusion and its significance in cancer is discussed.

Bacterial Involvement in Progression and Metastasis of Colorectal Neoplasia

While the gut microbiome is composed of numerous bacteria, specific bacteria within the gut may play a significant role in carcinogenesis, progression, and metastasis of colorectal carcinoma (CRC). Certain microbial species are known to be associated with specific cancers; however, the interrelationship between bacteria and metastasis is still enigmatic. Mounting evidence suggests that bacteria participate in cancer organotropism during solid tumor metastasis. A critical review of the literature was conducted to better characterize what is known about bacteria populating a distant site and whether a tumor depends upon the same microenvironment during or after metastasis. The processes of carcinogenesis, tumor growth and metastatic spread in the setting of bacterial infection were examined in detail. The literature was scrutinized to discover the role of the lymphatic and venous systems in tumor metastasis and how microbes affect these processes. Some bacteria have a potent ability to enhance epithelial–mesenchymal transition, a critical step in the metastatic cascade. Bacteria also can modify the microenvironment and the local immune profile at a metastatic site. Early targeted antibiotic therapy should be further investigated as a measure to prevent metastatic spread in the setting of bacterial infection.

Cell fusion as a link between the SARS-CoV-2 spike protein, COVID-19 complications, and vaccine side effects

A distinctive feature of the SARS-CoV-2 spike protein is its ability to efficiently fuse cells, thus producing syncytia found in COVID-19 patients. This commentary proposes how this ability enables spike to cause COVID-19 complications as well as side effects of COVID-19 vaccines, and suggests how these effects can be prevented.

Colon cancer cells acquire immune regulatory molecules from tumor-infiltrating lymphocytes by trogocytosis

Cancer cells can develop an immunosuppressive tumor microenvironment to control tumor-infiltrating lymphocytes. The underlying mechanisms still remain unclear. Here, we report that mouse and human colon cancer cells acquire lymphocyte membrane proteins including cellular markers such as CD4 and CD45. We observed cell populations harboring both a tumor-specific marker and CD4 in the tumor microenvironment. Sorted cells from these populations were capable of forming organoids, identifying them as cancer cells. Live imaging analysis revealed that lymphocyte membrane proteins were transferred to cancer cells via trogocytosis. As a result of the transfer in vivo, cancer cells also acquired immune regulatory surface proteins such as CTLA4 and Tim3, which suppress activation of immune cells [T. L. Walunas et al, Immunity 1, 405-413 (1994) and L. Monney et al., Nature 415, 536-541 (2002)]. RNA sequencing analysis of ex vivo-cocultured splenocytes with trogocytic cancer cells showed reductions in Th1 activation and natural killer cell signaling pathways compared with the nontrogocytic control. Cancer cell trogocytosis was confirmed in the patient-derived xenograft models of colorectal cancer and head and neck cancer. These findings suggest that cancer cells utilize membrane proteins expressed in lymphocytes, which in turn contribute to the development of the immunosuppressive tumor microenvironment.

Microtubule Targeting Agents in Disease: Classic Drugs, Novel Roles

Microtubule-targeting agents (MTAs) represent one of the most successful first-line therapies prescribed for cancer treatment. They interfere with microtubule (MT) dynamics by either stabilizing or destabilizing MTs, and in culture, they are believed to kill cells via apoptosis after eliciting mitotic arrest, among other mechanisms. This classical view of MTA therapies persisted for many years. However, the limited success of drugs specifically targeting mitotic proteins, and the slow growing rate of most human tumors forces a reevaluation of the mechanism of action of MTAs. Studies from the last decade suggest that the killing efficiency of MTAs arises from a combination of interphase and mitotic effects. Moreover, MTs have also been implicated in other therapeutically relevant activities, such as decreasing angiogenesis, blocking cell migration, reducing metastasis, and activating innate immunity to promote proinflammatory responses. Two key problems associated with MTA therapy are acquired drug resistance and systemic toxicity. Accordingly, novel and effective MTAs are being designed with an eye toward reducing toxicity without compromising efficacy or promoting resistance. Here, we will review the mechanism of action of MTAs, the signaling pathways they affect, their impact on cancer and other illnesses, and the promising new therapeutic applications of these classic drugs.

Hybrid Formation and Fusion of Cancer Cells In Vitro and In Vivo

Simple Summary

Cell fusion as a fundamental biological process is required for various physiological processes, including fertilization, placentation, myogenesis, osteoclastogenesis, and wound healing/tissue regeneration. However, cell fusion is also observed during pathophysiological processes like tumor development. Mesenchymal stroma/stem-like cells (MSC) which play an important role within the tumor microenvironment like other cell types such as macrophages can closely interact and hybridize with cancer cells. The formation of cancer hybrid cells can involve various different mechanisms whereby the genomic parts of the hybrid cells require rearrangement to form a new functional hybrid cell. The fusion of cancer cells with neighboring cell types may represent an important mechanism during tumor development since cancer hybrid cells are detectable in various tumor tissues. During this rare event with resulting genomic instability the cancer hybrid cells undergo a post-hybrid selection process (PHSP) to reorganize chromosomes of the two parental nuclei whereby the majority of the hybrid population undergoes cell death. The remaining cancer hybrid cells survive by displaying altered properties within the tumor tissue.

Abstract

The generation of cancer hybrid cells by intra-tumoral cell fusion opens new avenues for tumor plasticity to develop cancer stem cells with altered properties, to escape from immune surveillance, to change metastatic behavior, and to broaden drug responsiveness/resistance. Genomic instability and chromosomal rearrangements in bi- or multinucleated aneuploid cancer hybrid cells contribute to these new functions. However, the significance of cell fusion in tumorigenesis is controversial with respect to the low frequency of cancer cell fusion events and a clonal advantage of surviving cancer hybrid cells following a post-hybrid selection process. This review highlights alternative processes of cancer hybrid cell development such as entosis, emperipolesis, cannibalism, therapy-induced polyploidization/endoreduplication, horizontal or lateral gene transfer, and focusses on the predominant mechanisms of cell fusion. Based upon new properties of cancer hybrid cells the arising clinical consequences of the subsequent tumor heterogeneity after cancer cell fusion represent a major therapeutic challenge.

Circulating Hybrid Cells: A Novel Liquid Biomarker of Treatment Response in Gastrointestinal Cancers

BACKGROUND

Real-time monitoring of treatment response with a liquid biomarker has potential to inform treatment decisions for patients with rectal adenocarcinoma (RAC), esophageal adenocarcinoma (EAC), and colorectal liver metastasis (CRLM). Circulating hybrid cells (CHCs), which have both immune and tumor cell phenotypes, are detectable in the peripheral blood of patients with gastrointestinal cancers, but their potential as an indicator of treatment response is unexplored.

METHODS

Peripheral blood specimens were collected from RAC and EAC patients after neoadjuvant therapy (NAT) or longitudinally during therapy and evaluated for CHC levels by immunostaining. Receiver operating characteristics (ROCs) and the Kaplan-Meier method were used to analyze the CHC level as a predictor of pathologic response to NAT and disease-specific survival (DSS), respectively.

RESULTS

Patients with RAC (n = 23) and EAC (n = 34) were sampled on the day of resection, and 11 patients (32%) demonstrated a pathologic complete response (pCR) to NAT. On ROC analysis, CHC levels successfully discriminated pCR from non-pCR with an area under the curve of 0.82 (95% confidence interval [CI], 0.71-0.92; P < 0.001). Additionally, CHC levels in the EAC patients correlated with residual nodal involvement (P = 0.026) and 1-year DSS (P = 0.029). The patients with RAC who were followed longitudinally during NAT (n = 2) and hepatic arterial infusion therapy for CRLM (n = 2) had CHC levels that decreased with therapy response and increased before clinical evidence of disease progression.

CONCLUSION

Circulating hybrid cells are a novel blood-based biomarker with potential for monitoring treatment response and disease progression to help guide decisions for further systemic therapy, definitive resection, and post-therapy surveillance. Additional validation studies of CHCs are warranted.

The somatic molecular evolution of cancer: Mutation, selection, and epistasis

Cancer progression has been attributed to somatic changes in single-nucleotide variants, copy-number aberrations, loss of heterozygosity, chromosomal instability, epistatic interactions, and the tumor microenvironment. It is not entirely clear which of these changes are essential and which are ancillary to cancer. The dynamic nature of cancer evolution in a patient can be illuminated using several concepts and tools from classical evolutionary biology. Neutral mutation rates in cancer cells are calculable from genomic data such as synonymous mutations, and selective pressures are calculable from rates of fixation occurring beyond the expectation by neutral mutation and drift. However, these cancer effect sizes of mutations are complicated by epistatic interactions that can determine the likely sequence of gene mutations. In turn, longitudinal phylogenetic analyses of somatic cancer progression offer an opportunity to identify key moments in cancer evolution, relating the timing of driver mutations to corresponding landmarks in the clinical timeline. These analyses reveal temporal aspects of genetic and phenotypic change during tumorigenesis and across clinical timescales. Using a related framework, clonal deconvolution, physical locations of clones, and their phylogenetic relations can be used to infer tumor migration histories. Additionally, genetic interactions with the tumor microenvironment can be analyzed with longstanding approaches applied to organismal genotype-by-environment interactions. Fitness landscapes for cancer evolution relating to genotype, phenotype, and environment could enable more accurate, personalized therapeutic strategies. An understanding of the trajectories underlying the evolution of neoplasms, primary, and metastatic tumors promises fundamental advances toward accurate and personalized predictions of therapeutic response.

Cellular and molecular actors of myeloid cell fusion: podosomes and tunneling nanotubes call the tune

Different types of multinucleated giant cells (MGCs) of myeloid origin have been described; osteoclasts are the most extensively studied because of their importance in bone homeostasis. MGCs are formed by cell-to-cell fusion, and most types have been observed in pathological conditions, especially in infectious and non-infectious chronic inflammatory contexts. The precise role of the different MGCs and the mechanisms that govern their formation remain poorly understood, likely due to their heterogeneity. First, we will introduce the main populations of MGCs derived from the monocyte/macrophage lineage. We will then discuss the known molecular actors mediating the early stages of fusion, focusing on cell-surface receptors involved in the cell-to-cell adhesion steps that ultimately lead to multinucleation. Given that cell-to-cell fusion is a complex and well-coordinated process, we will also describe what is currently known about the evolution of F-actin-based structures involved in macrophage fusion, i.e., podosomes, zipper-like structures, and tunneling nanotubes (TNT). Finally, the localization and potential role of the key fusion mediators related to the formation of these F-actin structures will be discussed. This review intends to present the current status of knowledge of the molecular and cellular mechanisms supporting multinucleation of myeloid cells, highlighting the gaps still existing, and contributing to the proposition of potential disease-specific MGC markers and/or therapeutic targets.

Cancer recurrence and lethality are enabled by enhanced survival and reversible cell cycle arrest of polyaneuploid cells

We present a unifying theory to explain cancer recurrence, therapeutic resistance, and lethality. The basis of this theory is the formation of simultaneously polyploid and aneuploid cancer cells, polyaneuploid cancer cells (PACCs), that avoid the toxic effects of systemic therapy by entering a state of cell cycle arrest. The theory is independent of which of the classically associated oncogenic mutations have already occurred. PACCs have been generally disregarded as senescent or dying cells. Our theory states that therapeutic resistance is driven by PACC formation that is enabled by accessing a polyploid program that allows an aneuploid cancer cell to double its genomic content, followed by entry into a nondividing cell state to protect DNA integrity and ensure cell survival. Upon removal of stress, e.g., chemotherapy, PACCs undergo depolyploidization and generate resistant progeny that make up the bulk of cancer cells within a tumor.

Spontaneous Fusion of MSC with Breast Cancer Cells Can Generate Tumor Dormancy

Direct cellular interactions of MDA-MB-231^cherry breast cancer cells with GFP-transduced human mesenchymal stroma/stem-like cells (MSC^GFP) in a co-culture model resulted in spontaneous cell fusion by the generation of MDA-MSC-hyb5^{cherry GFP} breast cancer hybrid cells. The proliferative capacity of MDA-MSC-hyb5 cells was enhanced about 1.8-fold when compared to the parental MDA-MB-231^cherry breast cancer cells. In contrast to a spontaneous MDA-MB-231^cherry induced tumor development in vivo within 18.8 days, the MDA-MSC-hyb5 cells initially remained quiescent in a dormancy-like state. At distinct time points after injection, NODscid mice started to develop MDA-MSC-hyb5 cell-induced tumors up to about a half year later. Following tumor initiation, however, tumor growth and formation of metastases in various different organs occurred rapidly within about 10.5 days. Changes in gene expression levels were evaluated by RNA-microarray analysis and revealed certain increase in dormancy-associated transcripts in MDA-MSC-hyb5. Chemotherapeutic responsiveness of MDA-MSC-hyb5 cells was partially enhanced when compared to MDA-MB-231 cells. However, some resistance, e.g., for taxol was detectable in cancer hybrid cells. Moreover, drug response partially changed during the tumor development of MDA-MSC-hyb5 cells; this suggests the presence of unstable in vivo phenotypes of MDA-hyb5 cells with increased tumor heterogeneity.

A melanoma patient with macrophage-cancer cell hybrids in the primary tumor, a lymph node metastasis and a brain metastasis

In 1911 it was proposed that cancer might result from fusion and hybridization between macrophages and cancer cells. Using immunohistochemistry it was determined that essentially all solid tumors expressed macrophage-like molecules on their cell surface. More recently we have used forensic (STR) genetics that allows one to detect DNA from more than one individual in the same sample. By studying biopsies from individuals receiving allogeneic stem cell transplants and later developed solid tumor metastases, we were able to detect both donor and patient DNA sequences suggesting that hybrids were present. Previously we found hybrids in biopsies of a renal cell carcinoma, a melanoma in a brain metastasis and a melanoma in a primary tumor with lymph node metastases. Here we have traced hybrids from a primary melanoma to an axillary lymph node to a brain metastasis. This is the first time that the entire metastatic process has been documented.

What can evolutionary biology learn from cancer biology?

Detecting and treating cancer effectively involves understanding the disease as one of somatic cell and tumor macroevolution. That understanding is key to avoid triggering an adverse reaction to therapy that generates an untreatable and deadly tumor population. Macroevolution differs from microevolution by karyotype changes rather than isolated localized mutations being the major source of hereditary variation. Cancer cells display major multi-site chromosome rearrangements that appear to have arisen in many different cases abruptly in the history of tumor evolution. These genome restructuring events help explain the punctuated macroevolutionary changes that mark major transitions in cancer progression. At least two different nonrandom patterns of rapid multisite genome restructuring - chromothripsis ("chromosome shattering") and chromoplexy ("chromosome weaving") - are clearly distinct in their distribution within the genome and in the cell biology of the stress-induced processes responsible for their occurrence. These observations tell us that eukaryotic cells have the capacity to reorganize their genomes rapidly in response to calamity. Since chromothripsis and chromoplexy have been identified in the human germline and in other eukaryotes, they provide a model for organismal macroevolution in response to the kinds of stresses that lead to mass extinctions.

Human cell polyploidization: The good and the evil

Therapeutic resistance represents a major cause of death for most lethal cancers. However, the underlying mechanisms of such resistance have remained unclear. The polyploid cells are due to an increase in DNA content, commonly associated with cell enlargement. In human, they play a variety of roles in physiology and pathologic conditions and perform the specialized functions during development, inflammation, and cancer. Recent work shows that cancer cells can be induced into polyploid giant cancer cells (PGCCs) that leads to reprogramming of surviving cancer cells to acquire resistance. In this article, we will review the polyploidy involved in development and inflammation, and the process of PGCCs formation and propagation that benefits to cell survival. We will discuss the potential opportunities in fighting resistant cancers. The increased knowledge of PGCCs will offer a completely new paradigm to explore the therapeutic intervention for lethal cancers.

Cell-cell fusions and cell-in-cell phenomena in healthy cells and cancer: Lessons from protists and invertebrates

Herein we analyze two special routes of the multinucleated cells' formation - the fusion of mononuclear cells and the formation of cell-in-cell structures - in the healthy tissues and in tumorigenesis. There are many theories of tumorigenesis based on the phenomenon of emergence of the hybrid cancer cells. We consider the phenomena, which are rarely mentioned in those theories: namely, cellularization of syncytium or coenocytes, and the reversible or irreversible somatogamy. The latter includes the short-term and the long-term vegetative (somatic) cells' fusions in the life cycles of unicellular organisms. The somatogamy and multinuclearity have repeatedly and independently emerged in various groups of unicellular eukaryotes. These phenomena are among dominant survival and biodiversity sustaining strategies in protists and we admit that they can likely play an analogous role in cancer cells.

Impact of the Tumor Microenvironment on Tumor Heterogeneity and Consequences for Cancer Cell Plasticity and Stemness

Tumor heterogeneity is considered the major cause of treatment failure in current cancer therapies. This feature of solid tumors is not only the result of clonal outgrowth of cells with genetic mutations, but also of epigenetic alterations induced by physical and chemical signals from the tumor microenvironment (TME). Besides fibroblasts, endothelial and immune cells, mesenchymal stroma/stem-like cells (MSCs) and tumor-associated macrophages (TAMs) intimately crosstalk with cancer cells and can exhibit both anti- and pro-tumorigenic effects. MSCs can alter cancer cellular phenotypes to increase cancer cell plasticity, eventually resulting in the generation of cancer stem cells (CSCs). The shift between different phenotypic states (phenotype switching) of CSCs is controlled via both genetic programs, such as epithelial-mesenchymal transdifferentiation or retrodifferentiation, and epigenetic alterations triggered by signals from the TME, like hypoxia, spatial heterogeneity or stromal cell-derived chemokines. Finally, we highlight the role of spontaneous cancer cell fusion with various types of stromal cells. i.e., MSCs in shaping CSC plasticity. A better understanding of cell plasticity and phenotype shifting in CSCs is a prerequisite for exploiting this phenomenon to reduce tumor heterogeneity, thereby improving the chance for therapy success.

The Intimate Relationship Among EMT, MET and TME: A T(ransdifferentiation) E(nhancing) M(ix) to Be Exploited for Therapeutic Purposes

Simple Summary

Intratumoral heterogeneity is considered the major cause of drug resistance and hence treatment failure in cancer patients. Tumor cells are known for their phenotypic plasticity that is the ability of a cell to reprogram and change its identity to eventually adopt multiple phenotypes. Tumor cell plasticity involves the reactivation of developmental programs, the acquisition of cancer stem cell properties and an enhanced potential for retro- or transdifferentiation. A well-known transdifferentiation mechanism is the process of epithelial-mesenchymal transition (EMT). Current evidence suggests a complex interplay between EMT, genetic and epigenetic alterations, and various signals from the tumor microenvironment (TME) in shaping a tumor cell’s plasticity. The vulnerabilities exposed by cancer cells when residing in a plastic or stem-like state have the potential to be exploited therapeutically, i.e., by converting highly metastatic cells into less aggressive or even harmless postmitotic ones.

Abstract

Intratumoral heterogeneity is considered the major cause of drug unresponsiveness in cancer and accumulating evidence implicates non-mutational resistance mechanisms rather than genetic mutations in its development. These non-mutational processes are largely driven by phenotypic plasticity, which is defined as the ability of a cell to reprogram and change its identity (phenotype switching). Tumor cell plasticity is characterized by the reactivation of developmental programs that are closely correlated with the acquisition of cancer stem cell properties and an enhanced potential for retrodifferentiation or transdifferentiation. A well-studied mechanism of phenotypic plasticity is the epithelial-mesenchymal transition (EMT). Current evidence suggests a complex interplay between EMT, genetic and epigenetic alterations, and clues from the tumor microenvironment in cell reprogramming. A deeper understanding of the connections between stem cell, epithelial–mesenchymal, and tumor-associated reprogramming events is crucial to develop novel therapies that mitigate cell plasticity and minimize the evolution of tumor heterogeneity, and hence drug resistance. Alternatively, vulnerabilities exposed by tumor cells when residing in a plastic or stem-like state may be exploited therapeutically, i.e., by converting them into less aggressive or even postmitotic cells. Tumor cell plasticity thus presents a new paradigm for understanding a cancer’s resistance to therapy and deciphering its underlying mechanisms.

Cancer cells employ an evolutionarily conserved polyploidization program to resist therapy

Unusually large cancer cells with abnormal nuclei have been documented in the cancer literature since 1858. For more than 100 years, they have been generally disregarded as irreversibly senescent or dying cells, too morphologically misshapen and chromatin too disorganized to be functional. Cell enlargement, accompanied by whole genome doubling or more, is observed across organisms, often associated with mitigation strategies against environmental change, severe stress, or the lack of nutrients. Our comparison of the mechanisms for polyploidization in other organisms and non-transformed tissues suggest that cancer cells draw from a conserved program for their survival, utilizing whole genome doubling and pausing proliferation to survive stress. These polyaneuploid cancer cells (PACCs) are the source of therapeutic resistance, responsible for cancer recurrence and, ultimately, cancer lethality.

ELAVL1 Role in Cell Fusion and Tunneling Membrane Nanotube Formations with Implication to Treat Glioma Heterogeneity

Homotypic and heterotypic cell fusions via permanent membrane fusions and temporal tunneling nanotube formations in the glioma microenvironment were recently documented in vitro and in vivo and mediate glioma survival, plasticity, and recurrence. Chronic inflammation, a hypoxic environment, aberrant mitochondrial function, and ER stress due to unfolded protein accumulation upregulate cell fusion events, which leads to tumor heterogeneity and represents an adaptive mechanism to promote tumor cell survival and plasticity in cytotoxic, nutrient-deprived, mechanically stressed, and inflammatory microenvironments. Cell fusion is a multistep process, which consists of the activation of the cellular stress response, autophagy formation, rearrangement of cytoskeletal architecture in the areas of cell-to-cell contacts, and the expression of proinflammatory cytokines and fusogenic proteins. The mRNA-binding protein of ELAV-family HuR is a critical node, which orchestrates the stress response, autophagy formation, cytoskeletal architecture, and the expression of proinflammatory cytokines and fusogenic proteins. HuR is overexpressed in gliomas and is associated with poor prognosis and treatment resistance. Our review provides a link between the HuR role in the regulation of cell fusion and tunneling nanotube formations in the glioma microenvironment and the potential suppression of these processes by different classes of HuR inhibitors.

Targeting of CD163+ Macrophages in Inflammatory and Malignant Diseases

The macrophage is a key cell in the pro- and anti-inflammatory response including that of the inflammatory microenvironment of malignant tumors. Much current drug development in chronic inflammatory diseases and cancer therefore focuses on the macrophage as a target for immunotherapy. However, this strategy is complicated by the pleiotropic phenotype of the macrophage that is highly responsive to its microenvironment. The plasticity leads to numerous types of macrophages with rather different and, to some extent, opposing functionalities, as evident by the existence of macrophages with either stimulating or down-regulating effect on inflammation and tumor growth. The phenotypes are characterized by different surface markers and the present review describes recent progress in drug-targeting of the surface marker CD163 expressed in a subpopulation of macrophages. CD163 is an abundant endocytic receptor for multiple ligands, quantitatively important being the haptoglobin-hemoglobin complex. The microenvironment of inflammation and tumorigenesis is particular rich in CD163⁺ macrophages. The use of antibodies for directing anti-inflammatory (e.g., glucocorticoids) or tumoricidal (e.g., doxorubicin) drugs to CD163⁺ macrophages in animal models of inflammation and cancer has demonstrated a high efficacy of the conjugate drugs. This macrophage-targeting approach has a low toxicity profile that may highly improve the therapeutic window of many current drugs and drug candidates.