Tumor dormancy due to failure of angiogenesis: role of the microenvironment

Altered tumor microenvironment heterogeneity of penile cancer during progression from non-lymphatic to lymphatic metastasis

BACKGROUND

Lymphatic metastasis is the major challenge in the treatment of penile cancer. The prognosis of individuals with lymphatic metastasis is extremely poor. Therefore, early identification of disease progression and lymphatic metastasis is an urgent task for researchers in penile cancer worldwide.

METHODS

In this study, using single-cell RNA sequencing, an immune landscape was established for the cancer ecosystem based on 46,861 cells from six patients with penile cancer (four with lymphatic metastasis [stage IV] and two without lymphatic metastasis [stage I]). Using bulk RNA sequencing, the discrepancy between the cancers and their respective metastatic lymph nodes was depicted based on seven patients with penile cancer.

RESULTS

The interaction between epithelial cells, fibroblasts, and endothelial cells, and the functional cooperation among invasion, epithelial-mesenchymal transition, and angiogenesis were found to be important landscapes in the penile cancer ecosystem, playing important roles in progression of cancer and lymph node metastasis.

CONCLUSIONS

This study is the first to investigate the altered tumor microenvironment heterogeneity of penile cancer as it evolves from non-lymphatic to lymphatic metastasis and provides insights into the mechanisms underlying malignant progression, the premetastatic niche, and lymphatic metastasis in penile cancer.

Autophagy in cancer immunotherapy: Perspective on immune evasion and cell death interactions

Both the innate and adaptive immune systems work together to produce immunity. Cancer immunotherapy is a novel approach to tumor suppression that has arisen in response to the ineffectiveness of traditional treatments like radiation and chemotherapy. On the other hand, immune evasion can diminish immunotherapy's efficacy. There has been a lot of focus in recent years on autophagy and other underlying mechanisms that impact the possibility of cancer immunotherapy. The primary feature of autophagy is the synthesis of autophagosomes, which engulf cytoplasmic components and destroy them by lysosomal degradation. The planned cell death mechanism known as autophagy can have opposite effects on carcinogenesis, either increasing or decreasing it. It is autophagy's job to maintain the balance and proper functioning of immune cells like B cells, T cells, and others. In addition, autophagy controls whether macrophages adopt the immunomodulatory M1 or M2 phenotype. The ability of autophagy to control the innate and adaptive immune systems is noteworthy. Interleukins and chemokines are immunological checkpoint chemicals that autophagy regulates. Reducing antigen presentation to induce immunological tolerance is another mechanism by which autophagy promotes cancer survival. Therefore, targeting autophagy is of importance for enhancing potential of cancer immunotherapy.

The evolving tumor microenvironment: From cancer initiation to metastatic outgrowth

Cancers represent complex ecosystems comprising tumor cells and a multitude of non-cancerous cells, embedded in an altered extracellular matrix. The tumor microenvironment (TME) includes diverse immune cell types, cancer-associated fibroblasts, endothelial cells, pericytes, and various additional tissue-resident cell types. These host cells were once considered bystanders of tumorigenesis but are now known to play critical roles in the pathogenesis of cancer. The cellular composition and functional state of the TME can differ extensively depending on the organ in which the tumor arises, the intrinsic features of cancer cells, the tumor stage, and patient characteristics. Here, we review the importance of the TME in each stage of cancer progression, from tumor initiation, progression, invasion, and intravasation to metastatic dissemination and outgrowth. Understanding the complex interplay between tumor cell-intrinsic, cell-extrinsic, and systemic mediators of disease progression is critical for the rational development of effective anti-cancer treatments.

Insights into the role of senescence in tumor dormancy: mechanisms and applications

One of the most formidable challenges in oncology and tumor biology research is to provide an accurate understanding of tumor dormancy mechanisms. Dormancy refers to the ability of tumor cells to go undetected in the body for a prolonged period, followed by "spontaneous" escape. Various models of dormancy have been postulated, including angiogenic, immune-mediated, and cellular dormancy. While the former two propose mechanisms by which tumor growth may remain static at a population level, cellular dormancy refers to molecular processes that restrict proliferation at the cell level. Senescence is a form of growth arrest, during which cells undergo distinct phenotypic, epigenetic, and metabolic changes. Senescence is also associated with the development of a robust secretome, comprised of various chemokines and cytokines that interact with the surrounding microenvironment, including other tumor cells, stromal cells, endothelial cells, and immune cells. Both tumor and non-tumor cells can undergo senescence following various stressors, many of which are present during tumorigenesis and therapy. As such, senescent cells are present within forming tumors and in residual tumors post-treatment and therefore play a major role in tumor biology. However, the contributions of senescence to dormancy are largely understudied. Here, we provide an overview of multiple processes that have been well established as being involved in tumor dormancy, and we speculate on how senescence may contribute to these mechanisms.

Regulation of dormancy during tumor dissemination: the role of the ECM

The study of the metastatic cascade has revealed the complexity of the process and the multiple cellular states that disseminated cancer cells must go through. The tumor microenvironment and in particular the extracellular matrix (ECM) plays an important role in regulating the transition from invasion, dormancy to ultimately proliferation during the metastatic cascade. The time delay from primary tumor detection to metastatic growth is regulated by a molecular program that maintains disseminated tumor cells in a non-proliferative, quiescence state known as tumor cell dormancy. Identifying dormant cells and their niches in vivo and how they transition to the proliferative state is an active area of investigation, and novel approaches have been developed to track dormant cells during dissemination. In this review, we highlight the latest research on the invasive nature of disseminated tumor cells and their link to dormancy programs. We also discuss the role of the ECM in sustaining dormant niches at distant sites.

The molecular basis of immuno-radiotherapy

PURPOSE

Radiotherapy (RT) and immunotherapy are powerful anti-tumor treatment modalities. Experimental research has demonstrated an important interplay between the cytotoxic effects of RT and the immune system. This systematic review provides an overview of the basics of anti-tumor immunity and focuses on the mechanisms underlying the interplay between RT and immune anti-tumor response that set the molecular basis of immuno-RT.

CONCLUSIONS

An 'immunity acquired equilibrium' mimicking tumor dormancy can be achieved post-irradiation treatment, with the balance shifted toward tumor eradication or regrowth when immune cells' cytotoxic effects or cancer proliferation rate prevail, respectively. RT has both immunosuppressive and immune-enhancing properties. The latter effect is also known as radio-vaccination. Its mechanisms involve up- or down-regulation of membrane molecules, such as PD-L1, HLA-class-I, CD80/86, CD47, and Fas/CD95, that play a vital role in immune checkpoint pathways and increased cytokine expression (e.g. INFα,β,γ, IL1,2, and TNFα) by cancer or immune cells. Moreover, the interactions of radiation with the tumor microenvironment (fibroblasts, tumor-infiltrating lymphocytes, monocytes, and dendritic cells are also an important component of radio-vaccination. Thus, RT may have anti-tumor vaccine properties, whose sequels can be exploited by immunotherapy agents to treat different cancer subtypes effectively.

Escape from breast tumor dormancy: The convergence of obesity and menopause

Obesity is associated with an increased risk of, and a poor prognosis for, postmenopausal (PM) breast cancer (BC). Our goal was to determine whether diet-induced obesity (DIO) promotes 1) shorter tumor latency, 2) an escape from tumor dormancy, and 3) an acceleration of tumor growth and to elucidate the underlying mechanism(s). We have developed in vitro assays and PM breast tumor models complemented by a noninvasive imaging system to detect vascular invasion of dormant tumors and have used them to determine whether obesity promotes the escape from breast tumor dormancy and tumor growth by facilitating the switch to the vascular phenotype (SVP) in PM BC. Obese mice had significantly higher tumor frequency, higher tumor volume, and lower overall survival compared with lean mice. We demonstrate that DIO exacerbates mammary gland hyperplasia and neoplasia, reduces tumor latency, and increases tumor frequency via an earlier acquisition of the SVP. DIO establishes a local and systemic proangiogenic and inflammatory environment via the up-regulation of lipocalin-2 (LCN2), vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF) that may promote the escape from tumor dormancy and tumor progression. In addition, we show that targeting neovascularization via a multitargeted receptor tyrosine kinase inhibitor, sunitinib, can delay the acquisition of the SVP, thereby prolonging tumor latency, reducing tumor frequency, and increasing tumor-free survival, suggesting that targeting neovascularization may be a potential therapeutic strategy in obesity-associated PM BC progression. This study establishes the link between obesity and PM BC and, for the first time to our knowledge, bridges the dysfunctional neovascularization of obesity with the earliest stages of tumor development.

The Genetic Basis of Dormancy and Awakening in Cutaneous Metastatic Melanoma

Immune dysregulation, in combination with genetic and epigenetic alterations, induces an excessive proliferation of uncontrolled melanoma cells followed by dissemination of the tumor cells to distant sites, invading organs and creating metastasis. Although immunotherapy, checkpoint inhibitors and molecular targeted therapies have been developed as treatment options for advanced melanoma, there are specific mechanisms by which cancer cells can escape treatment. One of the main factors associated with reduced response to therapy is the ability of residual tumor cells to persist in a dormant state, without proliferation. This comprehensive review aimed at understanding the genetic basis of dormancy/awakening phenomenon in metastatic melanoma will help identify the possible therapeutical strategies that might eliminate melanoma circulating tumor cells (CTCs) or keep them in the dormant state forever, thereby repressing tumor relapse and metastatic spread.

Dormancy: There and Back Again

Many cells are capable of maintaining viability in a non-dividing state with minimal metabolism under unfavorable conditions. These are germ cells, adult stem cells, and microorganisms. Unfortunately, a resting state, or dormancy, is possible for tuberculosis bacilli in a latent form of the disease and cancer cells, which may later form secondary tumors (metastases) in different parts of the body. These cells are resistant to therapy that can destroy intensely dividing cells and to the host immune system. A cascade of reactions that allows cells to enter and exit dormancy is triggered by regulatory factors from the microenvironment in niches that harbor the cells. A ratio of forbidding and permitting signals dictates whether the cells become dormant or start proliferation. The only difference between the cell dormancy regulation in normal and pathological conditions is that pathogens, mycobacteria, and cancer cells can influence their own fate by changing their microenvironment. Certain mechanisms of these processes are considered in the review.

Quercetin Can Inhibit Angiogenesis via the Down Regulation of MALAT1 and MIAT LncRNAs in Human Umbilical Vein Endothelial Cells

Background:

Angiogenesis is an important step in cancer metastasis since it enables the growing tumor to receive nutrients and oxygen. Quercetin is a generic flavonoid and has been investigated for its ability to inhibit angiogenesis in different types of cancers. MALAT1 and MIAT lncRNAs are associated with the angiogenesis process. MALAT1 induces hypoxia-driven angiogenesis via the overexpression of angiogenic genes. Down regulation of MIAT1 could inhibit the proliferation of endothelial cells, tube formation, and migration. In this study, we assessed the anti-angiogenic activity of quercetin on human umbilical vein endothelial cells (HUVEC) via the expression of MALAT1 and MIAT genes.

Methods:

In the present study, HUVEC cells were incubated with various concentrations of quercetin for 24, 48, and 72 h. Cell proliferation was then evaluated by MTT assay. RNA was extracted by TRIzol and cDNA synthesis. The expression levels of MALAT1 and MIAT genes relative to the GAPDH gene were quantified using the highly sensitive real-time PCR method.

Results:

Our results demonstrated that quercetin has an inhibitory impact on the cell viability of HUVEC cells. The IC₅₀ values of quercetin after 24, 48, and 72 h were 282.05 μM, 228.25 μM, and 131.65 μM, respectively. The MALAT1/GAPDH ratio was computed as 0.21 for 24h, 0.18 for 48h, and 0.29 for 72 h. The MIAT/GAPDH ratio was computed as 0.82 for 24h, 0.84 for 48h, and 0.78 for 72 h.

Conclusions:

In conclusion, quercetin treatment had an anti-angiogenic effect on HUVEC cells, at least partially via the down regulation of MALAT1 and MIAT LncRNAs gene expression.

Cellular heterogeneity and microenvironmental control of skin cancer

Healthy tissues harbour a surprisingly high number of cells that carry well-known cancer-causing mutations without impacting their physiological function. In recent years, strong evidence accumulated that the immediate environment of mutant cells profoundly impact their prospect of malignant progression. In this review, focusing on the skin, we investigate potential key mechanisms that ensure tissue homeostasis despite the presence of mutant cells, as well as critical factors that may nudge the balance from homeostasis to tumour formation. Functional in vivo studies and single-cell transcriptome analyses have revealed a tremendous cellular heterogeneity and plasticity within epidermal (stem) cells and their respective niches, revealing for example wild-type epithelial cells, fibroblasts or immune-cell subsets as critical in preventing cancer formation and malignant progression. It's the same cells, however, that can drive carcinogenesis. Therefore, understanding the abundance and molecular variation of cell types in health and disease, and how they interact and modulate the local signalling environment will thus be key for new therapeutic avenues in our battle against cancer.

Partial hepatectomy enhances the growth of CC531 rat colorectal cancer cells both in vitro and in vivo

Partial hepatectomy (PHx) is the gold standard for the treatment of colorectal cancer liver metastases. However, after removing a substantial amount of hepatic tissue, growth factors are released to induce liver regeneration, which may promote the proliferation of liver micrometastases or circulating tumour cells still present in the patient. The aim of this study is to assess the effect of PHx on the growth of liver metastases induced by intrasplenic cell inoculation as well as on in vitro proliferation of the same cancer cell line. Liver tumours were induced in 18 WAG/RijHsd male rats, by seeding 250,000 syngeneic colorectal cancer cells (CC531) into the spleen. The left lateral lobe of the liver was mobilized and in half of the animals it was removed to achieve a 40% hepatectomy. Twenty-eight days after tumour induction, the animals were sacrificed and the liver was removed and sliced to assess the relative tumour surface area (RTSA%). CC531 cells were cultured in presence of foetal calf serum, non-hepatectomised (NRS) or hepatectomized rat serum (HRS), and their proliferation rate at 24, 48, and 72 h was measured. RTSA% was significantly higher in animals which had undergone PHx than in the controls (non-hepatectomised) (46.98 ± 8.76% vs. 18.73 ± 5.65%; p < 0.05). Analysing each lobe separately, this difference in favour of hepatectomized animals was relevant and statistically significant in the paramedian and caudate lobes. But in the right lobe the difference was scarce and not significant. In vitro, 2.5% HRS achieved stronger proliferative rates than the control cultures (10% FCS) or their equivalent of NRS. In this experimental model, a parallelism has been shown between the effect of PHx on the growth of colorectal cancer cells in the liver and the effect of the serum on those cells in vitro.

On measuring selection in cancer from subclonal mutation frequencies

Recently available cancer sequencing data have revealed a complex view of the cancer genome containing a multitude of mutations, including drivers responsible for cancer progression and neutral passengers. Measuring selection in cancer and distinguishing drivers from passengers have important implications for development of novel treatment strategies. It has recently been argued that a third of cancers are evolving neutrally, as their mutational frequency spectrum follows a 1/f power law expected from neutral evolution in a particular intermediate frequency range. We study a stochastic model of cancer evolution and derive a formula for the probability distribution of the cancer cell frequency of a subclonal driver, demonstrating that driver frequency is biased towards 0 and 1. We show that it is difficult to capture a driver mutation at an intermediate frequency, and thus the calling of neutrality due to a lack of such driver will significantly overestimate the number of neutrally evolving tumors. Our approach provides quantification of the validity of the 1/f statistic across the entire range of relevant parameter values. We also show that our conclusions remain valid for non-exponential models: spatial 3d model and sigmoidal growth, relevant for early- and late stages of cancer growth.

Tumor Cell Dormancy: Threat or Opportunity in the Fight against Cancer

Tumor dormancy, a clinically undetectable state of cancer, makes a major contribution to the development of multidrug resistance (MDR), minimum residual disease (MRD), tumor outgrowth, cancer relapse, and metastasis. Despite its high incidence, the whole picture of dormancy-regulated molecular programs is far from clear. That is, it is unknown when and which dormant cells will resume proliferation causing late relapse, and which will remain asymptomatic and harmless to their hosts. Thus, identification of dormancy-related culprits and understanding their roles can help predict cancer prognosis and may increase the probability of timely therapeutic intervention for the desired outcome. Here, we provide a comprehensive review of the dormancy-dictated molecular mechanisms, including angiogenic switch, immune escape, cancer stem cells, extracellular matrix (ECM) remodeling, metabolic reprogramming, miRNAs, epigenetic modifications, and stress-induced p38 signaling pathways. Further, we analyze the possibility of leveraging these dormancy-related molecular cues to outmaneuver cancer and discuss the implications of such approaches in cancer treatment.

The link between wound healing and escape from tumor dormancy

Tumor dormancy is considered one of the major unsolved questions in cancer biology. Understanding the mechanisms responsible for maintaining and interrupting dormancy would be a major step towards preventing overt metastatic disease. Increasing evidence points to tissue trauma and subsequent wound healing as contributing events in escape from dormancy. In this review, we outline relevant aspects of the wound healing process, and relate this to mechanisms of tumor dormancy and metastatic progression. In addition to important findings in epidemiological and experimental studies, more direct evidence of such a link has recently been presented. These results can have major implications for treatment and prevention of cancer.

IL-1β inflammatory response driven by primary breast cancer prevents metastasis-initiating cell colonization

Lack of insight into mechanisms governing breast cancer metastasis has precluded the development of curative therapies. Metastasis-initiating cancer cells (MICs) are uniquely equipped to establish metastases, causing recurrence and therapeutic resistance. Using various metastasis models, we discovered that certain primary tumours elicit a systemic inflammatory response involving interleukin-1β (IL-1β)-expressing innate immune cells that infiltrate distant MIC microenvironments. At the metastatic site, IL-1β maintains MICs in a ZEB1-positive differentiation state, preventing MICs from generating highly proliferative E-cadherin-positive progeny. Thus, when the inherent plasticity of MICs is impeded, overt metastases cannot be established. Ablation of the pro-inflammatory response or inhibition of the IL-1 receptor relieves the differentiation block and results in metastatic colonization. Among patients with lymph node-positive breast cancer, high primary tumour IL-1β expression is associated with better overall survival and distant metastasis-free survival. Our data reveal complex interactions that occur between primary tumours and disseminated MICs that could be exploited to improve patient survival.

Control in dormancy or eradication of cancer stem cells: Mathematical modeling and stability issues

OBJECTIVE

Modeling and analysis of cell population dynamics enhance our understanding of cancer. Here we introduce and explore a new model that may apply to many tissues.

ANALYSES

An age-structured model describing coexistence between mutated and ordinary stem cells is developed and explored. The model is transformed into a nonlinear time-delay system governing the dynamics of healthy cells, coupled to a nonlinear differential-difference system describing dynamics of unhealthy cells. Its main features are highlighted and an advanced stability analysis of several steady states is performed, through specific Lyapunov-like functionals for descriptor-type systems.

RESULTS

We propose a biologically based model endowed with rich dynamics. It incorporates a new parameter representing immunoediting processes, including the case where proliferation of cancer cells is locally kept under check by the immune cells. It also considers the overproliferation of cancer stem cells, modeled as a subpopulation of mutated cells that is constantly active in cell division. The analysis that we perform here reveals the conditions of existence of several steady states, including the case of cancer dormancy, in the coupled model of interest. Our study suggests that cancer dormancy may result from a plastic sensitivity of mutated cells to their shared environment, different from that - fixed - of healthy cells, and this is related to an action (or lack of action) of the immune system. Next, the stability analysis that we perform is essentially oriented towards the determination of sufficient conditions, depending on all the model parameters, that ensure either a regionally (i.e., locally) stable dormancy steady state or eradication of unhealthy cells. Finally, we discuss some biological interpretations, with regards to our findings, in light of current and emerging therapeutics. These final insights are particularly formulated in the paradigmatic case of hematopoiesis and acute leukemia, which is one of the best known malignancies for which it is always hard, in presence of a clinical and histological remission, to decide between cure and dormancy of a tumoral clone.

Case Series: Abscopal Benefit of Surgery in 3 Immunotherapy-Treated Patients With Unresectable Cancer

For all of the optimism that immunotherapy has engendered, the flip side is that 7/10 patients with susceptible tumor types do not respond, while in nonsusceptible tumor types the response rates are significantly lower. In contradiction of the current orthodoxy against surgery in the setting of unresectable disease, we present 3 examples of immunotherapy-treated patients with widespread recurrence who experienced dramatic clinical improvement following debulking/metastasectomy. Taken together with examples from the literature that correlate longer survival with surgical intervention during treatment with immunotherapy, these 3 cases suggest that a new paradigm involving a wider role for surgery in the management of these patients should be explored. Possible mechanisms by which surgery may synergize with immunotherapy and improve outcomes are also discussed.

Does metronomic chemotherapy induce tumor angiogenic dormancy? A review of available preclinical and clinical data

Tumor dormancy is the ability of cancer cells to survive in a non-proliferating state. This condition can depend on three main mechanisms: cell cycle arrest (quiescence or cell dormancy), immunosurveillance (immunologic dormancy), or lack of functional blood vessels (angiogenic dormancy). In particular, under angiogenic dormancy, cancer cell proliferation is counterbalanced by apoptosis owing to poor vascularization, impeding tumor mass expansion beyond a microscopic size, with an asymptomatic and non-metastatic state. Tumor vasculogenic or non-angiogenic switch is essential to promote escape from tumor dormancy, leading to tumor mass proliferation and metastasis. In avascular lesions angiogenesis process results blocked from the equilibrium between pro- and anti-angiogenic factors, such as vascular endothelial growth factor (VEGF) and thrombospondin-1 (TSP-1), respectively. The angiogenic switch mainly depends on the disruption of this balance, in favor of pro-angiogenic factors, and on the recruitment of circulating endothelial progenitors (CEPs) that promote the formation of new blood vessels. Metronomic chemotherapy, the regular intake of doses able to sustain low but active concentrations of chemotherapeutic drugs during protracted time periods, is an encouraging therapeutic approach that has shown to upregulate anti-angiogenic factors such as TSP-1 and decline pro-angiogenic factors such as VEGF, suppressing the proangiogenic cells such as CEPs. In this perspective, metronomic chemotherapy may be one of the available therapeutic approaches capable to modulate favorably the angiogenic tumor dormancy, but further research is essential to better define this particular characteristic.

A Comprehensive Procedure to Evaluate the In Vitro Performance of the Putative Hemangioblastoma Neovascularization Using the Spheroid Sprouting Assay

The inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene plays a crucial role in the development of hemangioblastomas (HBs) within the human central nervous system (CNS). However, both the cytological origin and the evolutionary process of HBs (including neovascularization) remain controversial, and anti-angiogenesis for VHL-HBs, based on classic HB angiogenesis, have produced disappointing results in clinical trials. One major obstacle to the successful clinical translation of anti-vascular treatment is the lack of a thorough understanding of neovascularization in this vascular tumor. In this article, we present a comprehensive procedure to evaluate in vitro whether classic tumor angiogenesis exists in HBs, as well as its role in HBs. With this procedure, researchers can accurately understand the complexity of HB neovascularization and identify the function of this common form of angiogenesis in HBs. These protocols can be used to evaluate the most promising anti-vascular therapy for tumors, which has high translational potential either for tumors treatment or for aiding in the optimization of the anti-angiogenic treatment for HBs in future translations. The results highlight the complexity of HB neovascularization and suggest that this common form angiogenesis is only a complementary mechanism in HB neovascularization.

Surgery-induced tumor growth in (metastatic) colorectal cancer

Metastatic colorectal cancer (mCRC) is a devastating disease causing 700.000 deaths annually worldwide. Metastases most frequently develop in the liver. Partial hepatectomy has dramatically improved clinical outcome and is the only curative treatment option for eligible patients with mCRC. Pre-clinical studies have shown that surgical procedures can have tumor-promoting local 'side-effects' such as hypoxia and inflammation, thereby altering the behaviour of residual tumor cells. In addition, systemically released factors following (colon or liver) surgery can act as a wakeup-call for dormant tumor cells in distant organs and/or help establish a pre-metastatic niche. Tumor handling during resection may also increase the number of circulating tumor cells. Despite the overwhelming amount of pre-clinical data demonstrating the pro-tumorigenic side effects of surgery, clinical evidence is scarce. Indications for hepatic surgery are rapidly increasing due to a rise in the incidence of mCRC and a trend towards more aggressive surgical treatment. Therefore, it is increasingly important to understand the principles of surgery-induced tumor growth, in order to devise perioperative or adjuvant strategies to further enhance long-term tumor control. In the current study we review the evidence for surgery-stimulated tumor growth and suggest strategies to assess the clinical relevance of such findings.

A Combination of Immune Checkpoint Inhibition with Metronomic Chemotherapy as a Way of Targeting Therapy-Resistant Cancer Cells

Therapeutic resistance remains a major obstacle in treating many cancers, particularly in advanced stages. It is likely that cytotoxic lymphocytes (CTLs) have the potential to eliminate therapy-resistant cancer cells. However, their effectiveness may be limited either by the immunosuppressive tumor microenvironment, or by immune cell death induced by cytotoxic treatments. High-frequency low-dose (also known as metronomic) chemotherapy can help improve the activity of CTLs by providing sufficient stimulation for cytotoxic immune cells without excessive depletion. Additionally, therapy-induced removal of tumor cells that compete for shared nutrients may also facilitate tumor infiltration by CTLs, further improving prognosis. Metronomic chemotherapy can also decrease the number of immunosuppressive cells in the tumor microenvironment, including regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs). Immune checkpoint inhibition can further augment anti-tumor immune responses by maintaining T cells in an activated state. Combining immune checkpoint inhibition with metronomic administration of chemotherapeutic drugs may create a synergistic effect that augments anti-tumor immune responses and clears metabolic competition. This would allow immune-mediated elimination of therapy-resistant cancer cells, an effect that may be unattainable by using either therapeutic modality alone.

The women in steady exercise research (WISER) survivor trial: The innovative transdisciplinary design of a randomized controlled trial of exercise and weight-loss interventions among breast cancer survivors with lymphedema

INTRODUCTION

Breast cancer survivors face dual challenges: long term sequelae of treatment, and risk of recurrent disease. Obesity and a sedentary lifestyle complicate both challenges. The WISER Survivor trial assessed the effects of exercise and/or weight-loss on lymphedema, biomarkers of breast cancer recurrence, and quality of life. We report on the innovative transdisciplinary design of this trial and report attrition rates.

METHODS

This one year trial randomized breast cancer survivors who had a BMI of ≥25kg/m2, were sedentary and had breast-cancer-related-lymphedema to 1) exercise (weight training and aerobic exercise) 2) weight-loss 3) exercise and weight-loss 4) or control group. Innovative aspects included: adaptation of a community-based weight training program to a largely home-based program; use of a commercial meal replacement system as part of the lifestyle modification weight-loss program; inclusion of measures of cost-effectiveness to enable economic evaluations; and alignment with a parallel mouse model for breast cancer recurrence to enable transdisciplinary research. In this model, mice bearing dormant residual tumor cells, which spontaneously relapse, were placed on a high-fat diet. Overweight animals were randomly assigned to exercise, calorie restriction, both, or control group and followed for cancer recurrence. The animal model will guide mechanistic biomarkers to be tested in the human trial.

RESULTS & DISCUSSION

351 participants were randomized; 13 experienced breast cancer recurrence during the trial. Of the 338 participants without recurrence, 83% completed the trial. The WISER Survivor trial will show the effects of exercise and weight-loss on lymphedema outcomes, biomarkers of recurrence and quality of life. NCT ClinicalTrials.gov registration #: NCT01515124.

Theranostic Role of 32P-ATP as Radiopharmaceutical for the Induction of Massive Cell Death within Avascular Tumor Core

Drug inaccessibility to vast areas of the tumor parenchyma is amongst the major hurdles for conventional therapies. Treatment efficacy rapidly decreases with distance from vessels and most of the tumor cells survive therapy. Also, between subsequent cycles of treatment, spared cancer cells replace those killed near the vessels, improving their access to nutrients, boosting their proliferation rate, and thus enabling tumor repopulation. Because of their property of "acting at a distance," radioisotopes are believed to overcome the physical barrier of vascular inaccessibility. Methods A novel molecular imaging tool called Cerenkov Luminescence Imaging (CLI) was employed for the detection of Cerenkov radiation emitted by beta particles, allowing in vivo tracking of beta-emitters. More precisely we investigated using a xenograft model of colon carcinoma the potential use of 32P-ATP as a novel theranostic radiopharmaceutical for tracing tumor lesions while simultaneously hampering their growth. Results Our analyses demonstrated that 32P-ATP injected into tumor-bearing mice reaches tumor lesions and persists for days and weeks within the tumor parenchyma. Also, the high-penetrating beta particles of 32P-ATP exert a "cross-fire" effect that induces massive cell death throughout the entire tumor parenchyma including core regions. Conclusion Our findings suggest 32P-ATP treatment as a potential approach to complement conventional therapies that fail to reach the tumor core and to prevent tumor repopulation.

The influence of vascular endothelial growth factor-A and matrix metalloproteinase-2 and -9 in angiogenesis, metastasis, and prognosis of endometrial cancer

Angiogenesis (the growth of new blood vessels) is essential in most of the body’s physiological processes, such as in the normal functioning of the endometrium during and after the menstrual cycle. Vascular endothelial growth factor (VEGF) and matrix metalloproteinase (MMP) are the mostly expressed angiogenic factors, especially, during the process of endometrial degeneration and remodeling. In carcinogenesis, tumor hypoxia-induced factors, through the process of “angiogenic switch”, stimulate the production of angiogenic factors, particularly VEGF and MMP. Subsequently, these angiogenic factors are associated with degradation, differentiation, proliferation, and migration of vascular endothelial cells, enhancing the formation of new blood vessels to supply the tumor with oxygen and nutrients. This process is equally significant for tumor development and metastasis. Hence, like in other cancers, the overexpression of MMP and VEGF in endometrial cancer (EC) seems to play a significant role in its tumorigenesis and metastasis. This research will discuss the influence of MMP and VEGF on angiogenesis, metastasis, and the prognosis of EC as well as the clinical importance of the factors in the diagnosis of EC.

Autophagy regulation and its role in gastric cancer and colorectal cancer

BACKGROUND

Autophagy is associated with the occurrence, development, cellular adaptation, progression, treatment and prognosis of gastric cancer (GC) and colorectal cancer (CRC). The effect of autophagy in these two cancers has attracted our attention.

OBJECTIVE

The aim of this study was to describe the functional and regulatory mechanisms associated with autophagy in GC and CRC.

METHODS

We reviewed recent publications describing the role of autophagy in GC and CRC, including the functional characteristics, clinical significance and regulatory mechanisms.

RESULTS

Autophagy plays context-dependent dual roles in the development and progression of GC and CRC. It can either promote tumor growth and cell survival or can contribute to tumor suppression and promote cell death. Both of these effects employ complex regulatory networks, such as those mediated by p53, PI3K/Akt/mTOR, Ras and microRNA. Among the cellular process associated with these pathways, autophagy is a potential target for anti-tumor therapy.

CONCLUSION

Autophagy is associated with both tumorigenic and protective effects in cancer. However, the role of autophagy in GC and CRC remains unclear. Although the translation of the basic science of autophagy into clinical practice is a long process, the modulation of autophagy as a potential therapeutic approach in GC and CRC merits further investigation.

Dormant Cells: The Original Cause of Tumor Recurrence and Metastasis

Tumor dormancy is one of the stages in tumor development without clinical symptoms. Tumor dormant cells may appear in early stages of tumor development, as well as in micrometastasis and minimal residual disease. The mechanism for the switch of dormant cells between quiescent and proliferative stages is still largely unknown. Potential mechanisms that may account for the transition between dormant tumor cells and proliferative cells include angiogenesis, immune response, cellular factors, and signaling pathways. The clinical and therapeutic importance of dormant cells requires further studies to provide therapeutic strategies for inhibition of metastasis and tumor recurrence.

An exactly solvable, spatial model of mutation accumulation in cancer

One of the hallmarks of cancer is the accumulation of driver mutations which increase the net reproductive rate of cancer cells and allow them to spread. This process has been studied in mathematical models of well mixed populations, and in computer simulations of three-dimensional spatial models. But the computational complexity of these more realistic, spatial models makes it difficult to simulate realistically large and clinically detectable solid tumours. Here we describe an exactly solvable mathematical model of a tumour featuring replication, mutation and local migration of cancer cells. The model predicts a quasi-exponential growth of large tumours, even if different fragments of the tumour grow sub-exponentially due to nutrient and space limitations. The model reproduces clinically observed tumour growth times using biologically plausible rates for cell birth, death, and migration rates. We also show that the expected number of accumulated driver mutations increases exponentially in time if the average fitness gain per driver is constant, and that it reaches a plateau if the gains decrease over time. We discuss the realism of the underlying assumptions and possible extensions of the model.

Primary and metastatic tumor dormancy as a result of population heterogeneity

Existence of tumor dormancy, or cancer without disease, is supported both by autopsy studies that indicate presence of microscopic tumors in men and women who die of trauma (primary dormancy), and by long periods of latency between excision of primary tumors and disease recurrence (metastatic dormancy). Within dormant tumors, two general mechanisms underlying the dynamics are recognized, namely, the population existing at limited carrying capacity (tumor mass dormancy), and solitary cell dormancy, characterized by long periods of quiescence marked by cell cycle arrest. Here we focus on mechanisms that precede the avascular tumor reaching its carrying capacity, and propose that dynamics consistent with tumor dormancy and subsequent escape from it can be accounted for with simple models that take into account population heterogeneity. We evaluate parametrically heterogeneous Malthusian, logistic and Allee growth models and show that 1) time to escape from tumor dormancy is driven by the initial distribution of cell clones in the population and 2) escape from dormancy is accompanied by a large increase in variance, as well as the expected value of fitness-determining parameters. Based on our results, we propose that parametrically heterogeneous logistic model would be most likely to account for primary tumor dormancy, while distributed Allee model would be most appropriate for metastatic dormancy. We conclude with a discussion of dormancy as a stage within a larger context of cancer as a systemic disease.

Reviewers: This article was reviewed by Heiko Enderling and Marek Kimmel.

Hypoxia induced CCL28 promotes angiogenesis in lung adenocarcinoma by targeting CCR3 on endothelial cells

Tumor hypoxia is one of the important features of lung adenocarcinoma. Chemokines might mediate the effects caused by tumor hypoxia. As confirmed in tumor tissue and serum of patients, CC chemokine 28 (CCL28) was the only hypoxia induced chemokine in lung adenocarcinoma cells. CCL28 could promote tube formation, migration and proliferation of endothelial cells. In addition, angiogenesis was promoted by CCL28 in the chick chorioallantoic membrane and matrigel implanted in dorsal back of athymic nude mice (CByJ.Cg-Foxn1^nu/J). Tumors formed by lung adenocarcinoma cells with high expression of CCL28 grew faster and had a higher vascular density, whereas tumor formation rate of lung adenocarcinoma cells with CCL28 expression knockdown was quite low and had a lower vascular density. CCR3, receptor of CCL28, was highly expressed in vascular endothelial cells in lung adenocarcinoma when examining by immunohistochemistry. Further signaling pathways in endothelial cells, modulated by CCL28, were analyzed by Phosphorylation Antibody Array. CCL28/CCR3 signaling pathway could bypass that of VEGF/VEGFR on the levels of PI3K-Akt, p38 MAPK and PLC gamma. The effects could be neutralized by antibody against CCR3. In conclusion, CCL28, as a chemokine induced by tumor hypoxia, could promote angiogenesis in lung adenocarcinoma through targeting CCR3 on microvascular endothelial cells.

Treatment Opportunities for Colorectal Liver Metastases

Colorectal liver metastases (CLM) are the most common hepatic malignancy and are caused by disseminated tumour cells (DTCs) seeded early in the tumourigenesis of colorectal cancer. Despite optimal treatment, CLM are associated with high mortality rates. This review provides an overview of three promising strategies to extend survival in CLM: treatment of DTCs, immunotherapy, and new surgical resection techniques.

Escape from tumor dormancy and time to angiogenic switch as mitigated by tumor-induced stimulation of stroma

A variety of mechanisms have been proposed to explain "cancer without disease", the state of tumor dormancy, characterized by balance in cell proliferation and cell death within a tumor. Here we have investigated a theoretical construct, whereby one of such mechanisms, the time to induction of angiogenesis, or "angiogenic switch", is mitigated by the degree of stromal stimulation by the tumor. We tested this hypothesis and its implications by introducing a mathematical model that captures how angiogenesis regulators, released from the platelet clot, contribute to formation of normal vasculature. We then modified the model to introduce tumor-induced increase in production of angiogenesis regulators and were able to simulate pathological angiogenesis. Through varying parameters governing the degree of tumor-induced stromal stimulation, we were able to qualitatively replicate experimentally observed growth curves for both dormant and actively growing tumors of breast cancer and liposarcoma. In fact, variation of very few parameters was sufficient to replicate any experimentally observed time to angiogenic switch in the available data. Finally, we investigated the effects of tighter binding isoforms of angiogenesis stimulators on neovasculature formation and tumor growth, which may provide an explanation for variations in angiogenesis -dependence in tumors of different tissue origin.

Procyanidin B2 3,3″-di-O-gallate inhibits endothelial cells growth and motility by targeting VEGFR2 and integrin signaling pathways

Targeting angiogenesis, one of the hallmarks of carcinogenesis, using non-toxic phytochemicals has emerged as a translational opportunity for angioprevention and to control advanced stages of malignancy. Herein, we investigated the inhibitory effects and associated mechanism/s of action of Procyanidin B2-3,3″-di- O-gallate (B2G2), a major component of grape seed extract, on human umbilical vein endothelial cells (HUVECs) and human prostate microvascular endothelial cells (HPMECs). Our results showed that B2G2 (10-40 μM) inhibits growth and induces death in both HUVECs and HPMECs. Additional studies revealed that B2G2 causes a G1 arrest in cell cycle progression of HUVECs by down-regulating cyclins (D1 and A), CDKs (Cdk2 and Cdc2) and Cdc25c phosphatase and up-regulating CDK inhibitors (p21 and p27) expression. B2G2 also induced strong apoptotic death in HUVECs through increasing p53, Bax and Smac/Diablo expression while decreasing Bcl-2 and survivin levels. Additionally, B2G2 inhibited the growth factors-induced capillary tube formation in HUVECs and HPMECs. Interestingly, conditioned media (CCM) from prostate cancer (PCA) cells (LNCaP and PC3) grown under normoxic (~21% O2) and hypoxic (1% O2) conditions significantly enhanced the tube formation in HUVECs, which was compromised in presence of conditioned media from B2G2-treated PCA cells. B2G2 also inhibited the motility and invasiveness of both HUVECs and HPMECs. Mechanistic studies showed that B2G2 targets VEGFR2/PI3K/Akt and integrin signaling molecules which are important for endothelial cells survival, proliferation, tube formation and motility. Overall, we report that B2G2 inhibits several attributes of angiogenesis in cell culture; therefore, it warrants further investigation for efficacy for angioprevention and cancer control.

Autophagy in colorectal cancer: An important switch from physiology to pathology

Colorectal cancer (CRC) remains a leading cause of cancer death in both men and women worldwide. Among the factors and mechanisms that are involved in the multifactorial etiology of CRC, autophagy is an important transformational switch that occurs when a cell shifts from normal to malignant. In recent years, multiple hypotheses have been considered regarding the autophagy mechanisms that are involved in cancer. The currently accepted hypothesis is that autophagy has dual and contradictory roles in carcinogenesis, but the precise mechanisms leading to autophagy in cancer are not yet fully defined and seem to be context dependent. Autophagy is a surveillance mechanism used by normal cells that protects them from the transformation to malignancy by removing damaged organelles and aggregated proteins and by reducing reactive oxygen species, mitochondrial abnormalities and DNA damage. However, autophagy also supports tumor formation by promoting access to nutrients that are critical to the metabolism and growth of tumor cells and by inhibiting cellular death and increasing drug resistance. Autophagy studies in CRC have focused on several molecules, mainly microtubule-associated protein 1 light chain 3, beclin 1, and autophagy related 5, with conflicting results. Beneficial effects were observed for some agents that modulate autophagy in CRC either alone or, more often, in combination with other agents. More extensive studies are needed in the future to clarify the roles of autophagy-related genes and modulators in colorectal carcinogenesis, and to develop potential beneficial agents for the prognosis and treatment of CRC.

The wound inflammatory response exacerbates growth of pre-neoplastic cells and progression to cancer

There is a long-standing association between wound healing and cancer, with cancer often described as a "wound that does not heal". However, little is known about how wounding, such as following surgery, biopsy collection or ulceration, might impact on cancer progression. Here, we use a translucent zebrafish larval model of Ras(G12V)-driven neoplasia to image the interactions between inflammatory cells drawn to a wound, and to adjacent pre-neoplastic cells. We show that neutrophils are rapidly diverted from a wound to pre-neoplastic cells and these interactions lead to increased proliferation of the pre-neoplastic cells. One of the wound-inflammation-induced trophic signals is prostaglandin E2 (PGE2). In an adult model of chronic wounding in zebrafish, we show that repeated wounding with subsequent inflammation leads to a greater incidence of local melanoma formation. Our zebrafish studies led us to investigate the innate immune cell associations in ulcerated melanomas in human patients. We find a strong correlation between neutrophil presence at sites of melanoma ulceration and cell proliferation at these sites, which is associated with poor prognostic outcome.

Imaging innate immune responses at tumour initiation: new insights from fish and flies

Recent imaging studies in genetically tractable and translucent zebrafish and Drosophila melanogaster models have opened a window on the earliest stages of tumorigenesis, when pre-neoplastic cells first arise in tissues before they progress into full-blown cancers. Innate immune cells often find these cells soon after they develop, but this efficient surveillance is not always good for the host because although immune cells have phagocytic capacity, they can also nurture the growing clones of pre-neoplastic cells. We describe these newly observed early interactions between immune cells and cancer cells and speculate on their potential clinical implications.

Metastasis prevention by targeting the dormant niche

Despite considerable advancements that shattered previously held dogmas about the metastatic cascade, the evolution of therapies to treat metastatic disease has not kept up. In this Opinion article, I argue that, rather than waiting for metastases to emerge before initiating treatment, it would be more effective to target metastatic seeds before they sprout. Specifically, I advocate directing therapies towards the niches that harbour dormant disseminated tumour cells to sensitize them to cytotoxic agents. Treatment sensitization, achieved by disrupting reservoirs of leukaemic stem cells and latent HIV, argues that this approach, although unconventional, could succeed in improving patient survival by delaying or even preventing metastasis.

Dormancy and growth of metastatic breast cancer cells in a bone-like microenvironment

Breast cancer can reoccur, often as bone metastasis, many years if not decades after the primary tumor has been treated. The factors that stimulate dormant metastases to grow are not known, but bone metastases are often associated with skeletal trauma. We used a dormancy model of MDA-MB-231BRMS1, a metastasis-suppressed human breast cancer cell line, co-cultured with MC3T3-E1 osteoblasts in a long term, three dimensional culture system to test the hypothesis that bone remodeling cytokines could stimulate dormant cells to grow. The cancer cells attached to the matrix produced by MC3T3-E1 osteoblasts but grew slowly or not at all until the addition of bone remodeling cytokines, TNFα and IL-β. Stimulation of cell proliferation by these cytokines was suppressed with indomethacin, an inhibitor of cyclooxygenase and of prostaglandin production, or a prostaglandin E2 (PGE2) receptor antagonist. Addition of PGE2 directly to the cultures also stimulated cell proliferation. MCF-7, non-metastatic breast cancer cells, remained dormant when co-cultured with normal human osteoblast and fibroblast growth factor. Similar to the MDA-MB-231BRMS1 cells, MCF-7 proliferation increased in response to TNFα and IL-β. These findings suggest that changes in the bone microenvironment due to inflammatory cytokines associated with bone repair or excess turnover may trigger the occurrence of latent bone metastasis.

Differentiation of lipoma and atypical lipomatous tumor by a scoring system: implication of increased vascularity on pathogenesis of liposarcoma

Background

Well-differentiated liposarcoma (WDL)/atypical lipomatous tumor (ALT) is considered a low-grade malignancy that rarely metastasizes but should be carefully followed because recurrence or dedifferentiation may occur. It is recognized that WDL and ALT are essentially synonymous, describing lesions that are identical both morphologically and karyotypically, and that site-specific variations in behavior relate only to surgical resectability. Preoperative differential diagnosis between lipoma and ALT has been well studied because their clinical and image characteristics are very similar. We evaluated the factors that may differentiate ALTs from lipomas, and validated a tentative scoring system for the diagnosis of the 2 tumor types.

Methods

Forty-eight lipomas and 12 ALTs were included. The mean age, location and depth of the tumor as well as the compartment were not significantly different between the 2 groups. To evaluate the vascularity of the tumors, the average number of intratumoral vessels on pathological sections was calculated and compared between cases of lipoma and ALT.

Results

The tumor size was significantly larger in ALT cases than in lipoma cases (P < 0.001). Magnetic resonance imaging (MRI) revealed septal structures in 91.6% of ALTs, whereas 20.8% of lipomas showed septa. Contrast enhancement in MRI was found significantly more often in ALTs (81.2%) than in lipomas (18.8%) (P < 0.001). We created a “ALT score” to discriminate between lipoma and ALT (0–6 points). ALT cases gave significantly higher point values (average 5.1 points) than lipoma cases (average 1.7 points) (P < 0.001). We found a significantly increased number of vessels in cases of ALT than in cases of lipoma (P = 0.001).

Conclusions

Our ALT score may help surgeons to differentiate a suspected ALT from a lipoma and could recommend a marginal resection in cases of suspected ALT. Increased intratumoral vascularity in ALT is reflected in the MRI findings and may play a key role in the acquisition of a malignant phenotype in adipocytic tumors.

Autophagy in cellular metabolism and cancer

Autophagy is a catabolic process mediated by incorporation of cellular material into cytosolic membrane vesicles for lysosomal degradation. It is crucial for maintaining cell viability and homeostasis in response to numerous stressful conditions. In this Review, the role of autophagy in both normal biology and disease is discussed. Emphasis is given to the interplay of autophagy with nutrient signaling through the ULK1 autophagy pre-initiation complex. Furthermore, related cellular processes utilizing components of the canonical autophagy pathway are discussed due to their potential roles in nutrient scavenging. Finally, the role of autophagy in cancer and its potential as a cancer therapeutic target are considered.

Hierarchy of breast cancer cells: key to reverse dormancy for therapeutic intervention

An understanding of how cancer cells adapt dormancy would allow for targeted treatment. The current literature suggests that the cancer stem cells might be the major cells with the ability to become quiescent and to resist current drug treatment. The properties of cancer stem cells and healthy stem cells are functionally similar, thereby posing a challenge to target the dormant cells. The bone marrow is particularly a challenge because the dormant breast cancer cells are close to the endosteum, which is also home to the endogenous hematopoietic stem cells. Here we discuss how research studies could bring an understanding of the cellular and molecular interactions between the cancer stem cells and cells within the bone marrow microenvironment. This will allow for intervention to reverse dormancy for targeted treatment. The treatment will require studies within the normal organ functions to ensure treatment without toxicity.

The role of gene regulatory networks in promoting cancer progression and metastasis

ABSTRACT: 

The majority of deaths owing to cancer are ultimately caused by metastatic disease. However, most research, to date, has focused on the molecular features of cancers at their primary sites rather than on understanding disseminated malignancy in its systemic form. The dynamic nature of metastatic malignancy and its behavior as a co-ordinated systemic disease require a cancer progression paradigm that is integrative and can incorporate both the proximate causes of cancer and the broader ultimate causes in an evolutionary and developmental context. The study of robust cellular attractor states that arise directly from the architectural patterns contained within gene regulatory networks is proposed as a conceptual framework through which many of the other disparate models of cancer metastasis can be more clearly viewed and, ultimately, unified, thus providing a new conceptual framework in which to understand cancer progression and metastasis.

Spontaneous reversion of the angiogenic phenotype to a nonangiogenic and dormant state in human tumors

The angiogenic switch, a rate-limiting step in tumor progression, has already occurred by the time most human tumors are detectable. However, despite significant study of the mechanisms controlling this switch, the kinetics and reversibility of the process have not been explored. The stability of the angiogenic phenotype was examined using an established human liposarcoma xenograft model. Nonangiogenic cells inoculated into immunocompromised mice formed microscopic tumors that remained dormant for approximately 125 days (vs. <40 days for angiogenic cells) whereupon the vast majority (>95%) initiated angiogenic growth with second-order kinetics. These original, clonally derived angiogenic tumor cells were passaged through four in vivo cycles. At each cycle, a new set of single-cell clones was established from the most angiogenic clone and characterized for in vivo for tumorigenic activity. A total of 132 single-cell clones were tested in the second, third, and fourth in vivo passage. Strikingly, at each passage, a portion of the single-cell clones formed microscopic, dormant tumors. Following dormancy, like the original cell line, these revertant tumors spontaneously switched to the angiogenic phenotype. Finally, revertant clones were transcriptionally profiled and their angiogenic output determined. Collectively, these data demonstrate that the angiogenic phenotype in tumors is malleable and can spontaneously revert to the nonangiogenic phenotype in a population of human tumor cells.

IMPLICATIONS

Leveraging the rate of reversion to the nonangiogenic phenotype and tumor dormancy may be a novel anticancer strategy.

Tissue factor expression provokes escape from tumor dormancy and leads to genomic alterations

The coagulation system links immediate (hemostatic) and late (inflammatory, angiogenic) tissue responses to injury, a continuum that often is subverted in cancer. Here we provide evidence that tumor dormancy is influenced by tissue factor (TF), the cancer cell-associated initiator of the coagulation system and a signaling receptor. Thus, indolent human glioma cells deficient for TF remain viable but permanently dormant at the injection site for nearly a year, whereas the expression of TF leads to a step-wise transition to latent and overt tumor growth phases, a process that is preceded by recruitment of vascular (CD105(+)) and myeloid (CD11b(+) and F4/80(+)) cells. Importantly, the microenvironment orchestrated by TF expression drives permanent changes in the phenotype, gene-expression profile, DNA copy number, and DNA methylation state of the tumor cells that escape from dormancy. We postulate that procoagulant events in the tissue microenvironment (niche) may affect the fate of occult tumor cells, including their biological and genetic progression to initiate a full-blown malignancy.

Carcinoma-associated fibroblasts provide operational flexibility in metastasis

Malignant cancer cells do not act as lone wolves to achieve metastasis, as they exist within a complex ecosystem consisting of an extracellular matrix scaffold populated by carcinoma-associated fibroblasts (CAFs), endothelial cells and immune cells. We recognize local (primary tumor) and distant ecosystems (metastasis). CAFs, also termed myofibroblasts, may have other functions in the primary tumor versus the metastasis. Cellular origin and tumor heterogeneity lead to the expression of specific markers. The molecular characteristics of a CAF remain in evolution since CAFs show operational flexibility. CAFs respond dynamically to a cancer cell's fluctuating demands by shifting profitable signals necessary in metastasis. Local, tissue-resident fibroblasts and mesenchymal stem cells (MSCs) coming from reservoir sites such as bone marrow and adipose tissue are the main progenitor cells of CAFs. CAFs may induce awakening from metastatic dormancy, a major cause of cancer-specific death. Cancer management protocols influence CAF precursor recruitment and CAF activation. Since CAF signatures represent early changes in metastasis, including formation of pre-metastatic niches, we discuss whether liquid biopsies, including exosomes, may detect and monitor CAF reactions allowing optimized prognosis of cancer patients.

Tumor dormancy and the neuroendocrine system: an undisclosed connection?

Tumor dormancy is a poorly understood phenomenon conceptualized as a protracted quiescent state during which cancer cells are present but clinical disease is not apparent, a condition referred to as "cancer without disease" by Folkman. Examples include the incidental detection of occult in situ tumors in post-mortem organ analysis and cancer recurrence after long disease-free periods. Lack of angiogenic competency has been proposed as a major determinant of the fate of dormant tumors. Other proposed processes include establishment of homeostatic equilibrium between tumor cells and the host's immune system response and a non-permissive microenvironment for tumor growth. Recent cellular and molecular studies suggest that neuroendocrine mediators regulate the biology of tumor progression and act as endogenous modulators of angiogenesis, inflammation, and other molecular processes involved in tumor reactivation from dormancy. We review experimental and clinical evidence and propose that neuroendocrine dynamics of the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis might contribute to the loss of tumor dormancy.

Rapid in vitro derivation of endothelium directly from human cancer cells

The development of an independent blood supply by a tumor is essential for maintaining growth beyond a certain limited size and for providing a portal for metastatic dissemination. Host-derived endothelial cells (ECs) residing in and compromising the tumor vasculature originate via distinct processes known as sprouting angiogenesis and vasculogenesis. More recently ECs originating directly from the tumor cells themselves have been described although the basis for this phenomenon remains poorly understood. Here we describe in vitro conditions that allow lung and ovarian cancer cells to undergo a rapid and efficient transition into ECs that are indistinguishable from those obtained in vivo. A variety of methods were used to establish that the acquired phenotypes and behaviors of these tumor-derived ECs (TDECs) closely resemble those of authentic ECs. Xenografts arising from co-inoculated in vitro-derived TDECs and tumor cells were also more highly vascularized than control tumors; moreover, their blood vessels were on average larger and frequently contained admixtures of host-derived ECs and TDECs derived from the initial inoculum. These results demonstrate that cancer cells can be manipulated under well-defined in vitro conditions to initiate a tumor cell-to-EC transition that is largely cell-autonomous, highly efficient and closely mimics the in vivo process. These studies provide a suitable means by which to identify and perhaps modify the earliest steps in TDEC generation.