Microenvironments dictating tumor cell dormancy

Epigenetic mechanisms in melanoma development and progression

Knowledge of cancer development and progression gained over the last few decades has enabled mapping of genetic and epigenetic changes unique to different phases of tumor evolution. Here we focus on epigenetic changes that drive melanoma development and progression. We highlight the importance of epigenetic mechanisms which encompass crosstalk with melanoma microenvironment that affect metastasis and therapy resistance. This review summarizes recent advances and describes potential strategies to leverage this knowledge to devise new therapies.

Drivers of centrosome abnormalities: Senescence progression and tumor immune escape

Centrosome abnormalities are a distinguishing feature of cancer and play a role in the aging process. Cancer cells may evade the immune system by activating immune checkpoints, altering their surrounding microenvironment, abnormalities in antigen presentation and recognition, and metabolic reprogramming to inhibit T-cell activity, allowing cancer cells to survive and spread within the host. When the centrosomes are abnormally shaped or numbered, mitotic errors can occur, cellular senescence occurs, cell death occurs, genomic instability occurs, and aneuploidy forms, resulting in diseases such as cancer. The present study is exploring the strategy of research progress in which centrosome abnormalities contribute to the aging process in various different ways as well as fuel immune escape from cancer cells, providing a new direction for cancer immunotherapy.

Apoptotic cell-derived extracellular vesicles-MTA1 confer radioresistance in cervical cancer by inducing cellular dormancy

BACKGROUND

Radioresistance presents a major challenge in the treatment of cervical cancer (CC). Apoptotic tumor cells can create an "onco-regenerative niche," contributing to radioresistance. However, the intercellular signaling mechanisms mediating the transfer of radioresistance from apoptotic to surviving cancer cells remain unclear.

METHODS

The role of apoptotic tumor cell-derived extracellular vesicles (apoEVs) in mediating radioresistance was investigated through integrated bioinformatics and experimental approaches. The GSE236738 dataset was analyzed to identify potential regulators, with subsequent validation of apoEV-MTA1 function using in vitro and in vivo models. Mechanistic studies focused on caspase-3 activation, p-STAT1 signaling pathway, and dormancy-associated protein networks. Furthermore, therapeutic strategies targeting MTA1 and its downstream signaling were evaluated for radiosensitization potential.

RESULTS

MTA1 was identified as a critical factor enriched in and transferred by apoEVs from apoptotic tumor cells to neighboring CC cells. Caspase-3 activation facilitated the nuclear export and encapsulation of MTA1 in apoEVs. Transferred MTA1 retained transcriptional activity, activated the p-STAT1 signaling pathway, and induced cellular dormancy via NR2F1, a key dormancy regulator, resulting in increased radioresistance. Knockdown of MTA1 in apoEVs or inhibition of p-STAT1 in recipient cells enhanced radiosensitivity. Furthermore, apoEV-MTA1 promoted tumor radioresistance and reduced survival rates in irradiated cervical cancer mouse model.

CONCLUSIONS

This study demonstrates that apoEV-MTA1 confers radioresistance in CC by promoting cellular dormancy via the p-STAT1/NR2F1 signaling axis. Targeting this pathway could improve radiosensitivity and provide a promising therapeutic strategy for CC patients.

Dormancy and awakening of cancer cells: the extracellular vesicle-mediated cross-talk between Dr. Jekill and Mr. Hyde

Cancer cell dormancy is a reversible process whereby cancer cells enter a quiescent state characterized by cell cycle arrest, inhibition of cell migration and invasion, and increased chemoresistance. Because of its reversibility and resistance to treatment, dormancy is a key process to study, monitor, and interfere with, in order to prevent tumor recurrence and metastasis and improve the prognosis of cancer patients. However, to achieve this goal, further studies are needed to elucidate the mechanisms underlying this complex and dynamic dual process. Here, we review the contribution of extracellular vesicles (EVs) to the regulation of cancer cell dormancy/awakening, focusing on the cross-talk between tumor and non-tumor cells in both the primary tumor and the (pre-)metastatic niche. Although EVs are recognized as key players in tumor progression and metastasis, as well as in tumor diagnostics and therapeutics, their role specifically in dormancy induction/escape is still largely elusive. We report on the most recent and promising results on this topic, focusing on the EV-associated nucleic acids involved. We highlight how EV studies could greatly contribute to the identification of dormancy signaling pathways and a dormancy/early awakening signature for the development of successful diagnostic/prognostic and therapeutic approaches.

The role of matrix metalloproteinase-2 in the metastatic cascade: a review

Matrix metalloproteinase-2 (MMP-2) is a gelatinase and is involved in multiple steps of the metastatic cascade. More than a decade ago an increased expression of MMP-2 in tumour cells or higher serum levels was reported to be a prognostic biomarker for a lower disease-free and overall survival rate. In recent years new evidence has indicated that MMP-2 has an important role in the tumour ecosystem. It is one of the many players in the onco-sphere, involved in interacting between tumour cells, host cells and the microenvironment. It plays a role in the dissemination of tumour cells, the epithelial–mesenchymal and mesenchymal–epithelial transitions, the formation of the pre-metastatic and metastatic niches, dormancy of tumour cells and modulating the immune system. The aim of this review is to highlight these multiple roles in the metastatic cascade and how many signalling pathways can up or down-regulate MMP-2 activity in the different stages of cancer progression and the effect of MMP-2 on the onco-sphere. Research in head and neck cancer is used as an example of these processes. The use of non-specific MMP inhibitors has been unsuccessful showing only limited benefits and associated with high toxicity as such that none have progressed past Phase III trials. Preclinical trials are undergoing using antibodies directed against specific matrix metalloproteinases, these targeted therapies may be potentially less toxic to the patients.

In Vivo Xenograft Model to Study Tumor Dormancy, Tumor Cell Dissemination and Metastasis

Metastasis is a complex, multistep process. To study the molecular steps of the metastatic cascade, it is important to use an in vivo system that recapitulates the complex tumor microenvironment. The chicken embryo chorioallantoic membrane (CAM) is an in vivo system suitable for the implantation of xenograft tumor models. It allows the study of different aspects of the metastatic process, including the dormancy-awakening transition. The main advantages of this system are its high reproducibility, cost-effectiveness, and versatility. Here, by using two dormancy tumor models, one of head and neck squamous cell carcinoma and one of breast cancer, we described a detailed protocol for the use of the CAM model in metastasis assays and for the study of tumor growth and dormancy.

Immunostaining for VEGF and Decorin Predicts Poor Survival and Recurrence in Canine Soft Tissue Sarcoma

The aim of this study was to investigate whether using immunohistochemistry to detect the angiogenic proteins vascular endothelial growth factor (VEGF) and decorin can help predict the risk of local recurrence of, or death from, canine soft tissue sarcoma (STS). VEGF and decorin were detected using validated immunohistochemical methods on 100 formalin-fixed paraffin-embedded samples of canine STS. The tumours had been resected previously, with clinical outcome determined by questionnaire. Each slide was assessed by light microscopy and the pattern of immunostaining with VEGF and decorin determined. Patterns of immunostaining were then analysed to detect associations with outcome measures of local recurrence and tumour-related death. High VEGF immunostaining was significantly (p < 0.001) associated with both increased local recurrence and reduced survival time. The distribution of decorin immunostaining within the tumour was significantly associated with survival time (p = 0.04) and local tumour recurrence (p = 0.02). When VEGF and decorin scores were combined, STS with both high VEGF and low decorin immunostaining were more likely to recur or cause patient death (p < 0.001). The results of this study suggest that immunostaining of VEGF and decorin may help predict the risk of local recurrence of canine STS.

KISS1 metastasis suppressor in tumor dormancy: a potential therapeutic target for metastatic cancers?

Present therapeutic approaches do not effectively target metastatic cancers, often limited by their inability to eliminate already-seeded non-proliferative, growth-arrested, or therapy-resistant tumor cells. Devising effective approaches targeting dormant tumor cells has been a focus of cancer clinicians for decades. However, progress has been limited due to limited understanding of the tumor dormancy process. Studies on tumor dormancy have picked up pace and have resulted in the identification of several regulators. This review focuses on KISS1, a metastasis suppressor gene that suppresses metastasis by keeping tumor cells in a state of dormancy at ectopic sites. The review explores mechanistic insights of KISS1 and discusses its potential application as a therapeutic against metastatic cancers by eliminating quiescent cells or inducing long-term dormancy in tumor cells.

The effect of denosumab on disseminated tumor cells (DTCs) of breast cancer patients with neoadjuvant treatment: a GeparX translational substudy

Background

Disseminated tumor cells (DTCs) in the bone marrow are observed in about 40% at primary diagnosis of breast cancer and predict poor survival. While anti-resorptive therapy with bisphosphonates was shown to eradicate minimal residue disease in the bone marrow, the effect of denosumab on DTCs, particularly in the neoadjuvant setting, is largely unknown. The recent GeparX clinical trial reported that denosumab, applied as an add-on treatment to nab-paclitaxel based neoadjuvant chemotherapy (NACT), did not improve the patient’s pathologic complete response (pCR) rate. Herein, we analyzed the predictive value of DTCs for the response to NACT and interrogated whether neoadjuvant denosumab treatment may eradicate DTCs in the bone marrow.

Methods

A total of 167 patients from the GeparX trial were analyzed for DTCs at baseline by immunocytochemistry using the pan-cytokeratin antibody A45-B/B3. Initially DTC-positive patients were re-analyzed for DTCs after NACT ± denosumab.

Results

At baseline, DTCs were observed in 43/167 patients (25.7%) in the total cohort, however their presence did not predict response to nab-paclitaxel based NACT (pCR rates: 37.1% in DTC-negative vs. 32.6% DTC-positive; p = 0.713). Regarding breast cancer subtypes, the presence of DTCs at baseline was numerically associated with response to NACT in TNBC patients (pCR rates: 40.0% in DTC-positive vs. 66.7% in DTC-negative patients; p = 0.16). Overall, denosumab treatment did not significantly increase the given DTC-eradication rate of NACT (NACT: 69.6% DTC-eradication vs. NACT + denosumab: 77.8% DTC-eradication; p = 0.726). In TNBC patients with pCR, a numerical but statistically non-significant increase of DTC-eradication after NACT + denosumab was observed (NACT: 75% DTC-eradication vs. NACT + denosumab: 100% DTC-eradication; p = 1.00).

Conclusion

This is the first study worldwide, demonstrating that neoadjuvant add-on denosumab over a short-term period of 24 months does not increase the DTC-eradication rate in breast cancer patients treated with NACT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-023-01619-2.

The metastatic niche formation: focus on extracellular vesicle-mediated dialogue between lung cancer cells and the microenvironment

Lung cancer is the deadliest cancer in the world, with the majority of patients presenting with advanced or metastatic disease at first diagnosis. The lungs are also one of the most common sites of metastasis from lung cancer and other tumors. Understanding the mechanisms that regulate metastasis formation from primary lung cancer and in the lungs is therefore fundamental unmet clinical need. One of the first steps during the establishment of lung cancer metastases includes the formation of the pre-metastatic niche (PMN) at distant organs, which may occur even during the early phases of cancer development. The PMN is established through intricate cross-talk between primary tumor-secreted factors and stromal components at distant sites. Mechanisms controlling primary tumor escape and seeding of distant organs rely on specific properties of tumor cells but are also tightly regulated by interactions with stromal cells at the metastatic niche that finally dictate the success of metastasis establishment. Here, we summarize the mechanisms underlying pre-metastatic niche formation starting from how lung primary tumor cells modulate distant sites through the release of several factors, focusing on Extracellular Vesicles (EVs). In this context, we highlight the role of lung cancer-derived EVs in the modulation of tumor immune escape. Then, we illustrate the complexity of Circulating Tumor Cells (CTCs) that represent the seeds of metastasis and how interactions with stromal and immune cells can help their metastatic dissemination. Finally, we evaluate the contribution of EVs in dictating metastasis development at the PMN through stimulation of proliferation and control of disseminated tumor cell dormancy. Overall, we present an overview of different steps in the lung cancer metastatic cascade, focusing on the EV-mediated interactions between tumor cells and stromal/immune cells.

Incidentally Detected Malignancies in Lung Explants

Introduction: Incidentally detected malignancies in lung explants portend risk of early cancer recurrence and metastases with posttransplant immunosuppression. We present a series of lung transplant recipients with previously unverified malignancies in native lung explants. Design: We reviewed the histopathology, radiographic imaging, and management of lung explant malignancies at our institution over 10 years (2011-2020). Endpoints were survival and allograft rejection. Results: An explant malignancy was found in 1.3% (11/855) of lung transplant recipients (6 [55%] men; median age 68 years; 6 [55%] ex-smokers [median pack-years, 25]). Nine (82%) were adenocarcinoma, 1 (9%) was squamous cell carcinoma (SCC), and 1 (9%) was follicular lymphoma. Three patients (27%) had multifocal involvement (≥3 lobes), 4 (36%) had nodal involvement, and the median (range) tumor size was 2.7 (0.4-19) cm. The median interval between last imaging and transplant was 58 (29-144) days. Mycophenolate mofetil was discontinued or reduced in all; everolimus was used in 2 patients, and cisplatin-pemetrexed chemotherapy was used in 2 patients. The prevalence of acute cellular rejection and chronic rejection was 27% and 9%, respectively. Lung recipients with cancer had significantly lower survival than those without (36.4% vs 67.3%, p = 0.002); median survival was 27 (17, 65) months in 4 recipients who were alive and cancer-free at the end of the study period. Conclusions: Unidentified malignancies, commonly adenocarcinoma, can be detected in explanted native lungs. Pneumonectomy may be curative in SCC, lymphoproliferative disorders, and stage I adenocarcinoma. Modulating immunosuppression to prevent allograft rejection and tumor proliferation is warranted.

Regulation of Metastatic Tumor Dormancy and Emerging Opportunities for Therapeutic Intervention

Cancer recurrence and metastasis, following successful treatment, constitutes a critical threat in clinical oncology and are the leading causes of death amongst cancer patients. This phenomenon is largely attributed to metastatic tumor dormancy, a rate-limiting stage during cancer progression, in which disseminated cancer cells remain in a viable, yet not proliferating state for a prolonged period. Dormant cancer cells are characterized by their entry into cell cycle arrest and survival in a quiescence state to adapt to their new microenvironment through the acquisition of mutations and epigenetic modifications, rendering them resistant to anti-cancer treatment and immune surveillance. Under favorable conditions, disseminated dormant tumor cells 're-awake', resume their proliferation and thus colonize distant sites. Due to their rarity, detection of dormant cells using current diagnostic tools is challenging and, thus, therapeutic targets are hard to be identified. Therefore, unraveling the underlying mechanisms required for keeping disseminating tumor cells dormant, along with signals that stimulate their "re-awakening" are crucial for the discovery of novel pharmacological treatments. In this review, we shed light into the main mechanisms that control dormancy induction and escape as well as emerging therapeutic strategies for the eradication of metastatic dormant cells, including dormancy maintenance, direct targeting of dormant cells and re-awakening dormant cells. Studies on the ability of the metastatic cancer cells to cease proliferation and survive in a quiescent state before re-initiating proliferation and colonization years after successful treatment, will pave the way toward developing innovative therapeutic strategies against dormancy-mediated metastatic outgrowth.

Recent insights into the effects of metabolism on breast cancer cell dormancy

Breast cancer (BC) remains the most common cancer, as well as the leading cause of cancer mortality in women worldwide [1]. Approximately 30% of patients with early-stage BC experience metastasis or a recurrent form of the disease [2]. The phenomenon of BC dormancy, where metastasised cancer cells remain in a quiescent phase at their disseminated location and for unknown reasons can become actively proliferative again, further adds to BC’s clinical burden with treatment at this secondary stage typically proving futile. An emerging avenue of research focuses on the metabolic properties of dormant BC cells (BCCs) and potential metabolic changes causing BCCs to enter/exit their quiescent state. Here we explore several studies that have uncovered changes in carbon metabolism underlying a dormant state, with conflicting studies uncovering shifts towards both glycolysis and/or oxidative phosphorylation. This review highlights that the metabolic states/shifts of dormant BCCs seem to be dependent on different BC subtypes and receptor status; however, more work needs to be done to fully map these differences. Building on the research that this review outlines could provide new personalised therapeutic possibilities for BC patients.

Cancer Immunoediting: Elimination, Equilibrium, and Immune Escape in Solid Tumors

Emphasizing the dynamic processes between cancer and host immune system, the initially discovered concept of cancer immunosurveillance has been replaced by the current concept of cancer immunoediting consisting of three phases: elimination, equilibrium, and escape. Solid tumors composed of both cancer and host stromal cells are an example how the three phases of cancer immunoediting functionally evolve and how tumor shaped by the host immune system gets finally resistant phenotype. The elimination, equilibrium, and escape have been described in this chapter in details, including the role of immune surveillance, cancer dormancy, disruption of the antigen-presenting machinery, tumor-infiltrating immune cells, resistance to apoptosis, as well as the function of tumor stroma, microvesicles, exosomes, and inflammation.

Chamaejasmenin B, an Inhibitor for Metastatic Outgrowth, Reversed M2-Dominant Macrophage Polarization in Breast Tumor Microenvironment

Metastasis is a multistep process that depends on the interactions between tumor cells and their microenvironment. Macrophages in the tumor microenvironment show high polarization plasticity and have a paradoxical role in cancer progression. Hijacked by tumor-promoting signals, the polarization status of macrophages was pathologically disturbed and believed to be the decisive mechanism forcing the progression of metastasis. In this study, we explored the immunological activity of Chamaejasmin B (ICJ), a previously proved inhibitor for metastasis, in macrophages from metastatic microenvironment. When intravenously injected of 4T1 cells in mice, ICJ significantly inhibited its metastatic outgrowth. Taking tumor cell and macrophage as a functional integrity, an adoptive transfer model was established in vitro to exclude the direct effect of ICJ on tumor. The findings suggest a dual influence of ICJ on both tumors and macrophages, as indicated by the rebalance of macrophage polarization and suppression of clonogenic potential in tumor cells. Mechanistically, ICJ redirected M2-dominant polarization of tumor-associated macrophage in an IL-4-mTOR-dependent manner. Collectively, our study revealed that ICJ rebalanced macrophage polarization in malignant microenvironment and showed promising effect in suppressing metastatic outgrowth in breast cancer model.

OUP accepted manuscript

Cell therapy using induced pluripotent stem cell (iPSC) derivatives may result in abnormal tissue generation because the cells undergo numerous cycles of mitosis before clinical application, potentially increasing the accumulation of genetic abnormalities. Therefore, genetic tests may predict abnormal tissue formation after transplantation. Here, we administered iPSC derivatives with or without single-nucleotide variants (SNVs) and deletions in cancer-related genes with various genomic copy number variant (CNV) profiles into immunodeficient mice and examined the relationships between mutations and abnormal tissue formation after transplantation. No positive correlations were found between the presence of SNVs/deletions and the formation of abnormal tissues; the overall predictivity was 29%. However, a copy number higher than 3 was correlated, with an overall predictivity of 86%. Furthermore, we found CNV hotspots at 14q32.33 and 17q12 loci. Thus, CNV analysis may predict abnormal tissue formation after transplantation of iPSC derivatives and reduce the number of tumorigenicity tests.

Extracellular Vesicles in Bone Tumors: How to Seed in the Surroundings Molecular Information for Malignant Transformation and Progression

Bone is a very dynamic tissue hosting different cell types whose functions are regulated by a plethora of membrane-bound and soluble molecules. Intercellular communication was recently demonstrated to be also sustained by the exchange of extracellular vesicles (EVs). These are cell-derived nanosized structures shuttling biologically active molecules, such as nucleic acids and proteins. The bone microenvironment is a preferential site of primary and metastatic tumors, in which cancer cells find a fertile soil to “seed and blossom”. Nowadays, many oncogenic processes are recognized to be sustained by EVs. For example, EVs can directly fuel the vicious cycle in the bone/bone marrow microenvironment. EVs create a favourable environment for tumor growth by affecting osteoblasts, osteoclasts, osteocytes, adipocytes, leukocytes, and endothelial cells. At the same time other crucial tumor-mediated events, such as the premetastatic niche formation, tumor cell dormancy, as well as drug resistance, have been described to be fostered by tumor-derived EVs. In this review, we will discuss the main body of literature describing how the cancer cells use the EVs for their growth into the bone and for educating the bone microenvironment to host metastases.

Inhibition of DEC2 is necessary for exiting cell dormancy in salivary adenoid cystic carcinoma

Background

Patients were prone to have poor prognosis once dormant tumor cells being reactivated. However, the molecular mechanism of tumor cell dormancy remains poorly understood. This study aimed to investigate the function of DEC2 in the dormancy of salivary adenoid cystic carcinoma (SACC) in vitro and vivo.

Methods

The function of DEC2 in tumor dormancy of SACC was investigated in nude mice by establishing primary and lung metastasis model. Meanwhile, the interaction between hypoxia and SACC dormancy and the role of DEC2 were demonstrated through CoCl₂ induced hypoxia–mimicking microenvironments. Furthermore, the expression of DEC2 was detected by immunohistochemical staining in primary SACC samples with and without recurrence.

Results

In the primary SACC, DEC2 overexpression inhibited cell proliferation, increased cell population arrested in G0/G1 phase, and participated in dormancy regulation, which limited tumor growth. Intriguingly, in the model of lung metastasis, the level of DEC2 was reduced significantly and resulted in dormancy exit and growth resumption of SACC cells. Then, we found that DEC2 may associate with hypoxia in contributing to tumor dormancy, which might provide a possible cue to explain the different roles of DEC2 in primary and metastasis lesions. And overexpression of DEC2 induced dormancy and promoted migration and invasion through activating EMT program. Finally, DEC2 positive expression was shown to be significantly correlated with recurrence and dormancy of SACC patients.

Conclusions

These findings provide a novel insight into the role of DEC2 gene in tumor dormancy and metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-01956-0.

Redefining macrophage and neutrophil biology in the metastatic cascade

Tumor cells metastasize to distant organs through a complex series of events that are driven by tumor intrinsic and extrinsic factors. In particular, non-malignant stromal cells, including immune cells, modify tumor metastatic behavior. Of these cells, tumor-associated innate immune cells, particularly macrophages and neutrophils, suppress the cytotoxic activity of innate and adaptive killer cells and interact with tumor cells to promote their growth and malignancy. These findings in mouse cancer models suggest that targeting these sub-populations of immune cells holds therapeutic promise in treating metastatic disease. In this review, we describe the origin and role of the macrophages, neutrophils, and their progenitors in the metastatic cascade and suggest strategies that might enhance cancer therapy.

Innovative Approaches in the Battle Against Cancer Recurrence: Novel Strategies to Combat Dormant Disseminated Tumor Cells

Cancer recurrence remains a great fear for many cancer survivors following their initial, apparently successful, therapy. Despite significant improvement in the overall survival of many types of cancer, metastasis accounts for ~90% of all cancer mortality. There is a growing understanding that future therapeutic practices must accommodate this unmet medical need in preventing metastatic recurrence. Accumulating evidence supports dormant disseminated tumor cells (DTCs) as a source of cancer recurrence and recognizes the need for novel strategies to target these tumor cells. This review presents strategies to target dormant quiescent DTCs that reside at secondary sites. These strategies aim to prevent recurrence by maintaining dormant DTCs at bay, or eradicating them. Various approaches are presented, including: reinforcing the niche where dormant DTCs reside in order to keep dormant DTCs at bay; promoting cell intrinsic mechanisms to induce dormancy; preventing the engagement of dormant DTCs with their supportive niche in order to prevent their reactivation; targeting cell-intrinsic mechanisms mediating long-term survival of dormant DTCs; sensitizing dormant DTCs to chemotherapy treatments; and, inhibiting the immune evasion of dormant DTCs, leading to their demise. Various therapeutic approaches, some of which utilize drugs that are already approved, or have been tested in clinical trials and may be considered for repurposing, will be discussed. In addition, clinical evidence for the presence of dormant DTCs will be reviewed, along with potential prognostic biomarkers to enable the identification and stratification of patients who are at high risk of recurrence, and who could benefit from novel dormant DTCs targeting therapies. Finally, we will address the shortcomings of current trial designs for determining activity against dormant DTCs and provide novel approaches.

Centrosome Dynamics and Its Role in Inflammatory Response and Metastatic Process

Metastasis is a process by which cancer cells escape from the location of the primary tumor invading normal tissues at distant organs. Chromosomal instability (CIN) is a hallmark of human cancer, associated with metastasis and therapeutic resistance. The centrosome plays a major role in organizing the microtubule cytoskeleton in animal cells regulating cellular architecture and cell division. Loss of centrosome integrity activates the p38-p53-p21 pathway, which results in cell-cycle arrest or senescence and acts as a cell-cycle checkpoint pathway. Structural and numerical centrosome abnormalities can lead to aneuploidy and CIN. New findings derived from studies on cancer and rare genetic disorders suggest that centrosome dysfunction alters the cellular microenvironment through Rho GTPases, p38, and JNK (c-Jun N-terminal Kinase)-dependent signaling in a way that is favorable for pro-invasive secretory phenotypes and aneuploidy tolerance. We here review recent data on how centrosomes act as complex molecular platforms for Rho GTPases and p38 MAPK (Mitogen activated kinase) signaling at the crossroads of CIN, cytoskeleton remodeling, and immune evasion via both cell-autonomous and non-autonomous mechanisms.

The Cancer Cell Dissemination Machinery as an Immunosuppressive Niche: A New Obstacle Towards the Era of Cancer Immunotherapy

Although cancer immunotherapy has resulted in unpreceded survival benefits to subsets of oncology patients, accumulating evidence from preclinical animal models suggests that the immunosuppressive tumor microenvironment remains a detrimental factor limiting benefit for many patient subgroups. Recent efforts on lymphocyte-mediated immunotherapies are primarily focused on eliminating cancer foci at primary and metastatic sites, but few studies have investigated the impact of these therapies on the highly complex process of cancer cell dissemination. The metastatic cascade involves the directional streaming of invasive/migratory tumor cells toward specialized blood vessel intravasation gateways, called TMEM doorways, to the peripheral circulation. Importantly, this process occurs under the auspices of a specialized tumor microenvironment, herewith referred to as "Dissemination Trajectory", which is supported by an ample array of tumor-associated macrophages (TAMs), skewed towards an M2-like polarization spectrum, and which is also vital for providing microenvironmental cues for cancer cell invasion, migration and stemness. Based on pre-existing evidence from preclinical animal models, this article outlines the hypothesis that dissemination trajectories do not only support the metastatic cascade, but also embody immunosuppressive niches, capable of providing transient and localized immunosubversion cues to the migratory/invasive cancer cell subpopulation while in the act of departing from a primary tumor. So long as these dissemination trajectories function as "immune deserts", the migratory tumor cell subpopulation remains efficient in evading immunological destruction and seeding metastatic sites, despite administration of cancer immunotherapy and/or other cytotoxic treatments. A deeper understanding of the molecular and cellular composition, as well as the signaling circuitries governing the function of these dissemination trajectories will further our overall understanding on TAM-mediated immunosuppression and will be paramount for the development of new therapeutic strategies for the advancement of optimal cancer chemotherapies, immunotherapies, and targeted therapies.

Could Extracellular Vesicles Contribute to Generation or Awakening of "Sleepy" Metastatic Niches?

Pre-metastatic niches provide favorable conditions for tumor cells to disseminate, home to and grow in otherwise unfamiliar and distal microenvironments. Tumor-derived extracellular vesicles are now recognized as carriers of key messengers secreted by primary tumors, signals that induce the formation of pre-metastatic niches. Recent evidence suggests that tumor cells can disseminate from the very earliest stages of primary tumor development. However, once they reach distal sites, tumor cells can persist in a dormant state for long periods of time until their growth is reactivated and they produce metastatic lesions. In this new scenario, the question arises as to whether extracellular vesicles could influence the formation of these metastatic niches with dormant tumor cells? (here defined as "sleepy niches"). If so, what are the molecular mechanisms involved? In this perspective-review article, we discuss the possible influence of extracellular vesicles in early metastatic dissemination and whether they might play a role in tumor cell dormancy. In addition, we comment whether extracellular vesicle-mediated signals may be involved in tumor cell awakening, considering the possibility that extracellular vesicles might serve as biomarkers to detect early metastasis and/or minimal residual disease (MRD) monitoring.

Minimal Residual Disease, Metastasis and Immunity

Progression from localized to metastatic disease requires cancer cells spreading to distant organs through the bloodstream. Only a small proportion of these circulating tumor cells (CTCs) survives dissemination due to anoikis, shear forces and elimination by the immune system. However, all metastases originate from CTCs capable of surviving and extravasating into distant tissue to re-initiate a tumor. Metastasis initiation is not always immediate as disseminated tumor cells (DTCs) may enter a non-dividing state of cell dormancy. Cancer dormancy is a reversible condition that can be maintained for many years without being clinically detectable. Subsequently, late disease relapses are thought to be due to cancer cells ultimately escaping from dormant state. Cancer dormancy is usually associated with minimal residual disease (MRD), where DTCs persist after intended curative therapy. Thus, MRD is commonly regarded as an indicator of poor prognosis in all cancers. In this review, we examine the current understanding of MRD and immunity during cancer progression to metastasis and discuss clinical perspectives for oncology.

Understanding ER+ Breast Cancer Dormancy Using Bioinspired Synthetic Matrices for Long-Term 3D Culture and Insights into Late Recurrence

Late recurrences of breast cancer are hypothesized to originate from disseminated tumor cells that re-activate after a long period of dormancy, ≥5 years for estrogen-receptor positive (ER+) tumors. An outstanding question remains as to what the key microenvironment interactions are that regulate this complex process, and well-defined human model systems are needed for probing this. Here, a robust, bioinspired 3D ER+ dormancy culture model is established and utilized to probe the effects of matrix properties for common sites of late recurrence on breast cancer cell dormancy. Formation of dormant micrometastases over several weeks is examined for ER+ cells (T47D, BT474), where the timing of entry into dormancy versus persistent growth depends on matrix composition and cell type. In contrast, triple negative cells (MDA-MB-231), associated with early recurrence, are not observed to undergo long-term dormancy. Bioinformatic analyses quantitatively support an increased "dormancy score" gene signature for ER+ cells (T47D) and reveal differential expression of genes associated with different biological processes based on matrix composition. Further, these analyses support a link between dormancy and autophagy, a potential survival mechanism. This robust model system will allow systematic investigations of other cell-microenvironment interactions in dormancy and evaluation of therapeutics for preventing late recurrence.

Site-specific metastasis: A cooperation between cancer cells and the metastatic microenvironment

The conclusion derived from the information provided in this review is that disseminating tumor cells (DTC) collaborate with the microenvironment of a future metastatic organ site in the establishment of organ‐specific metastasis. We review the basic principles of site‐specific metastasis and the contribution of the cross talk between DTC and the microenvironment of metastatic sites (metastatic microenvironment [MME]) to the establishment of the organ‐specific premetastatic niche; the targeted migration of DTC to the endothelium of the future organ‐specific metastasis; the transmigration of DTC to this site and the seeding and colonization of DTC in their future MME. We also discuss the role played by DTC‐MME interactions on tumor dormancy and on the differential response of tumor cells residing in different MMEs to antitumor therapy. Finally, we summarize some studies dealing with the effects of the MME on a unique site‐specific metastasis—brain metastasis.

The Quest for Improving Treatment of Cancer of Unknown Primary (CUP) Through Molecularly-Driven Treatments: A Systematic Review

Background: Carcinomas of unknown primary (CUP) account for 3–5% of all malignancy and, despite a reduction in incidence, the overall survival has not improved over the last decade. Chemotherapy regimens have not provided encouraging results. New diagnostic technologies, such as next generation sequencing (NGS), could represent a chance to identify potentially targetable genomic alterations in order to personalize treatment of CUP and provide insights into tumor biology.

Methods: A systematic review of studies of patients with CUP, whose tumor specimen was evaluated through a NGS panel, has been performed on June 10th, 2019 according to PRISMA criteria from PubMed, ASCO meeting library and Clinicaltrial.gov. We have identified potentially targetable alterations for which approved/off-label/in clinical trials drugs are available. Moreover, we have included case reports about CUP patients treated with targeted therapies driven by NGS results in order to explore the clinical role of NGS in this setting.

Results: We have evaluated 15 publications of which eleven studies (9 full-text articles and 2 abstracts) have analyzed the genomic profiling of CUPs through NGS technology, with different platforms and with different patients cohorts, ranging from 16 to 1,806 patients. Among all these studies, 85% of patients demonstrated at least one molecular alteration, the most frequent involving TP53 (41.88%), KRAS (18.81%), CDKN2A (8.8%), and PIK3CA (9.3%). A mean of 47.3% of patients harbored a potentially targetable alteration for which approved/off-label/in clinical trials drugs were available. Furthermore, we have identified 4 case reports in order to evaluate the clinical relevance of a specific targeted therapy identified through NGS.

Conclusions: NGS may represent a tool to improve diagnosis and treatment of CUP by identifying therapeutically actionable alterations and providing insights into tumor biology.

Frontiers in Intravital Multiphoton Microscopy of Cancer

Background

Cancer is a highly complex disease which involves the co-operation of tumor cells with multiple types of host cells and the extracellular matrix. Cancer studies which rely solely on static measurements of individual cell types are insufficient to dissect this complexity. In the last two decades, intravital microscopy has established itself as a powerful technique that can significantly improve our understanding of cancer by revealing the dynamic interactions governing cancer initiation, progression and treatment effects, in living animals. This review focuses on intravital multiphoton microscopy (IV-MPM) applications in mouse models of cancer.

Recent Findings

IV-MPM studies have already enabled a deeper understanding of the complex events occurring in cancer, at the molecular, cellular and tissue levels. Multiple cells types, present in different tissues, influence cancer cell behavior via activation of distinct signaling pathways. As a result, the boundaries in the field of IV-MPM are continuously being pushed to provide an integrated comprehension of cancer. We propose that optics, informatics and cancer (cell) biology are co-evolving as a new field. We have identified four emerging themes in this new field. First, new microscopy systems and image processing algorithms are enabling the simultaneous identification of multiple interactions between the tumor cells and the components of the tumor microenvironment. Second, techniques from molecular biology are being exploited to visualize subcellular structures and protein activities within individual cells of interest, and relate those to phenotypic decisions, opening the door for "in vivo cell biology". Third, combining IV-MPM with additional imaging modalities, or omics studies, holds promise for linking the cell phenotype to its genotype, metabolic state or tissue location. Finally, the clinical use of IV-MPM for analyzing efficacy of anti-cancer treatments is steadily growing, suggesting a future role of IV-MPM for personalized medicine.

Conclusion

IV-MPM has revolutionized visualization of tumor-microenvironment interactions in real time. Moving forward, incorporation of novel optics, automated image processing, and omics technologies, in the study of cancer biology, will not only advance our understanding of the underlying complexities but will also leverage the unique aspects of IV-MPM for clinical use.

APPLICATION OF DNA-DIRECTED PATTERNING TO FABRICATE AN IN VITRO BONE MARROW MICROENVIRONMENT FOR THE HIGH-THROUGHPUT STUDY OF PROSTATE CANCER DORMANCY

In metastatic cancer, the secondary microenvironment consists of numerous cell types, each signaling with, and potentially supporting, the disseminated tumor cell. However, in vitro models have thus far been limited in their complexity, ultimately hindering study. To overcome this, we report the optimization and application of a high-throughput method, DNA-directed patterning, to pattern different cell types from the bone marrow microenvironment for the study of prostate cancer proliferation within this environment. We show that cells in our patterned microenvironment maintain their phenotype and behavior. Moreover, we demonstrate the successful introduction of prostate cancer cells in our microenvironment to investigate dormancy.

Tunable hydrogels for controlling phenotypic cancer cell states to model breast cancer dormancy and reactivation

During metastasis, disseminated tumor cells (DTCs) from the primary tumor infiltrate secondary organs and reside there for varying lengths of time prior to forming new tumors. The time delay between infiltration and active proliferation, known as dormancy, mediates the length of the latency period. DTCs may undergo one of four fates post-infiltration: death, cellular dormancy, dormant micrometastasis, or invasive growth which, is in part, mediated by extracellular matrix (ECM) properties. Recapitulation of these cell states using engineered hydrogels could facilitate the systematic and controlled investigation of the mechanisms by which ECM properties influence DTC fate. Toward this goal, we implemented a set of sixteen hydrogels with systematic variations in chemical (ligand (RGDS) density and enzymatic degradability) and mechanical (elasticity, swelling, mesh size) properties to investigate their influence on the fate of encapsulated metastatic breast cancer cells, MDA-MB-231. Cell viability, apoptosis, proliferation, metabolic activity, and morphological measurements were acquired at five-day intervals over fifteen days in culture. Analysis of the phenotypic metrics indicated the presence of four different cell states that were classified as: (1) high growth, (2) moderate growth, (3) single cell, restricted survival, dormancy, or (4) balanced dormancy. Correlating hydrogel properties with the resultant cancer cell state indicated that ligand (RGDS) density and enzymatic degradability likely had the most influence on cell fate. Furthermore, we demonstrate the ability to reactivate cells from the single cell, dormant state to the high growth state through a dynamic increase in ligand (RGDS) density after forty days in culture. This tunable engineered hydrogel platform offers insight into matrix properties regulating tumor dormancy, and the dormancy-proliferation switch, and may provide future translational benefits toward development of anti-dormancy therapeutic strategies.

Metastatic Latency, a Veiled Threat

Metastatic relapse is observed in cancer patients with no clinical evidence of disease for months to decades after initial diagnosis and treatment. Disseminated cancer cells that are capable of entering reversible cell cycle arrest are believed to be responsible for these late metastatic relapses. Dynamic interactions between the latent disseminated tumor cells and their surrounding microenvironment aid cancer cell survival and facilitate escape from immune surveillance. Here, we highlight findings from preclinical models that provide a conceptual framework to define and target the latent metastatic phase of tumor progression. The hope is by identifying patients harboring latent metastatic cells and providing therapeutic options to eliminate metastatic seeds prior to their emergence will result in long lasting cures.

Mathematical Modeling Reveals That the Administration of EGF Can Promote the Elimination of Lymph Node Metastases by PD-1/PD-L1 Blockade

In the advanced stages of cancers like melanoma, some of the malignant cells leave the primary tumor and infiltrate the neighboring lymph nodes (LNs). The interaction between secondary cancer and the immune response in the lymph node represents a complex process that needs to be fully understood in order to develop more effective immunotherapeutic strategies. In this process, antigen-presenting cells (APCs) approach the tumor and initiate the adaptive immune response for the corresponding antigen. They stimulate the naive CD4+ and CD8+ T lymphocytes which subsequently generate a population of helper and effector cells. On one hand, immune cells can eliminate tumor cells using cell-cell contact and by secreting apoptosis inducing cytokines. They are also able to induce their dormancy. On the other hand, the tumor cells are able to escape the immune surveillance using their immunosuppressive abilities. To study the interplay between tumor progression and the immune response, we develop two new models describing the interaction between cancer and immune cells in the lymph node. The first model consists of partial differential equations (PDEs) describing the populations of the different types of cells. The second one is a hybrid discrete-continuous model integrating the mechanical and biochemical mechanisms that define the tumor-immune interplay in the lymph node. We use the continuous model to determine the conditions of the regimes of tumor-immune interaction in the lymph node. While we use the hybrid model to elucidate the mechanisms that contribute to the development of each regime at the cellular and tissue levels. We study the dynamics of tumor growth in the absence of immune cells. Then, we consider the immune response and we quantify the effects of immunosuppression and local EGF concentration on the fate of the tumor. Numerical simulations of the two models show the existence of three possible outcomes of the tumor-immune interactions in the lymph node that coincide with the main phases of the immunoediting process: tumor elimination, equilibrium, and tumor evasion. Both models predict that the administration of EGF can promote the elimination of the secondary tumor by PD-1/PD-L1 blockade.

Biomaterial Platform To Establish a Hypoxic Metastatic Niche in Vivo

Hypoxia is a hallmark of tumor microenvironments, exerting wide-ranging impacts on key processes of tumor progression and metastasis. However, our understanding of how hypoxia regulates these processes has been based primarily on studying the effects of hypoxia within the primary tumor. Recently, an increasing number of studies have suggested the importance of hypoxic regulation within metastatic target organs, but hypoxic metastatic niches in the body are difficult to access with current imaging techniques, hampering detailed in vivo investigation of hypoxia at metastatic sites. Here, we report an engineered biomaterial scaffold that is able to establish an in vivo hypoxic metastatic niche in a readily accessible area, enabling the investigation of hypoxic regulation at a metastatic site. We engineered hypoxic environments within microporous poly(lactide-co-glycolide) (PLG) scaffolds, which have previously been shown to act as premetastatic niche mimics, via the addition of CoCl2, a hypoxia-mimetic agent. When implanted into the subcutaneous region of mice, CoCl2-containing PLG (Co-PLG) scaffolds established hypoxic microenvironments, as evidenced by the stabilization of hypoxia-inducible factor 1α (HIF1α) and increased blood vessel formation in vitro and in vivo. Furthermore, implanted Co-PLG scaffolds were able to recruit 4T1 metastatic breast cancer cells. These results demonstrate that Co-PLG scaffolds can establish an in vivo hypoxic metastatic niche, providing a novel platform to investigate hypoxic regulation of disseminated tumor cells (DTCs) at target organs.

Engineered In Vitro Models of Tumor Dormancy and Reactivation

Metastatic recurrence is a major hurdle to overcome for successful control of cancer-associated death. Residual tumor cells in the primary site, or disseminated tumor cells in secondary sites, can lie in a dormant state for long time periods, years to decades, before being reactivated into a proliferative growth state. The microenvironmental signals and biological mechanisms that mediate the fate of disseminated cancer cells with respect to cell death, single cell dormancy, tumor mass dormancy and metastatic growth, as well as the factors that induce reactivation, are discussed in this review. Emphasis is placed on engineered, in vitro, biomaterial-based approaches to model tumor dormancy and subsequent reactivation, with a focus on the roles of extracellular matrix, secondary cell types, biochemical signaling and drug treatment. A brief perspective of molecular targets and treatment approaches for dormant tumors is also presented. Advances in tissue-engineered platforms to induce, model, and monitor tumor dormancy and reactivation may provide much needed insight into the regulation of these processes and serve as drug discovery and testing platforms.

Hyaluronan arrests human breast cancer cell growth by prolonging the G0/G1 phase of the cell cycle

In clinical breast cancer patients, quiescent disseminated tumor cells (DTCs) can persist for a long time in the bone marrow (BM) under the influence of microenvironmental cues. As a high molecular weight polysaccharide, hyaluronan (HA) not only has been shown to regulate cancer processes including cell invasion, metastasis, migration, and proliferation, but also is a major component of the BM extracellular matrix. Here, we tested whether HA promotes breast cancer cell quiescence through detecting cell proliferation, cell cycle phase distribution, and the expression of cell cycle-related regulator proteins. In our results, HA slowed the growth and prolonged the G0/G1 phase of the highly metastatic, bone-seeking human breast cancer MDA-MB-231BO cell line, which is consistent with results that HA activated p38α/β, inhibited phospho-ERK1/2 levels and reduced the ERK/p38 signaling ratio. Additionally, we examined the crucial cell cycle factors p21cip1 and Cyclin D1, both of which influence the transition from G1 to S phase. The results revealed that p21cip1 expression was up-regulated by HA, which was consequently accompanied by a decrease in Cyclin D1 level. Further research with a 3D culture model indicated that HA maintained low Ki-67 and high p21cip1 expression levels in MDA-MB-231BO cells. In summary, our work revealed that HA might contribute to DTC quiescence.

Cellular Phenotype Plasticity in Cancer Dormancy and Metastasis

Cancer dormancy is a period of cancer progression in which residual tumor cells exist, but clinically remain asymptomatic for a long time, as well as resistant to conventional chemo- and radiotherapies. Cellular phenotype plasticity represents that cellular phenotype could convert between epithelial cells and cells with mesenchymal traits. Recently, this process has been shown to closely associate with tumor cell proliferation, cancer dormancy and metastasis. In this review, we have described different scenarios of how the transition from epithelial to mesenchymal morphology (EMT) and backwards (MET) are connected with the initiation of dormancy and reactivation of proliferation. These processes are fundamental for cancer cells to invade tissues and metastasize. Recognizing the mechanisms underlying the cellular phenotype plasticity as well as dormancy and targeting them is likely to increase the efficiency of traditional tumor treatment inhibiting tumor metastasis.

TGF-β receptors: In and beyond TGF-β signaling

Transforming growth factor β (TGF-β) plays an important role in normal development and homeostasis. Dysregulation of TGF-β responsiveness and its downstream signaling pathways contribute to many diseases, including cancer initiation, progression, and metastasis. TGF-β ligands bind to three isoforms of the TGF-β receptor (TGFBR) with different affinities. TGFBR1 and 2 are both serine/threonine and tyrosine kinases, but TGFBR3 does not have any kinase activity. They are necessary for activating canonical or noncanonical signaling pathways, as well as for regulating the activation of other signaling pathways. Another prominent feature of TGF-β signaling is its context-dependent effects, temporally and spatially. The diverse effects and context dependency are either achieved by fine-tuning the downstream components or by regulating the expressions and activities of the ligands or receptors. Focusing on the receptors in events in and beyond TGF-β signaling, we review the membrane trafficking of TGFBRs, the kinase activity of TGFBR1 and 2, the direct interactions between TGFBR2 and other receptors, and the novel roles of TGFBR3.

Cellular Constituents of the Prostate Stroma: Key Contributors to Prostate Cancer Progression and Therapy Resistance

Reciprocal signaling between prostate stroma and its epithelium are fundamental to organ development and homeostasis. Similarly, interactions between tumor cells and stromal constituents are central to key aspects of carcinogenesis and malignancy growth involving tumor cell invasion, dissemination, and growth in distant sites. The prostate stroma is complex with several distinct resident cell types, infiltrating nonresident cell types and an amalgam of structural matrix factors, matricellular proteins, metabolites, growth factors, and cytokines. Of importance, the stroma is dynamic with changes in composition as a cause or consequence of intrinsic and extrinsic factors. In the context of epithelial neoplasia, the prostate stroma undergoes phenotypic changes with a loss of well-differentiated smooth muscle cell population and the expansion of cancer-associated fibroblast populations. This reactive stroma further coevolves with tumor progression. Recent studies show the role of tumor microenvironment components in therapy resistance and highlight the importance of a thorough knowledge of cross talk between tumor cells and microenvironment niches to develop new therapeutic strategies.

Cutting to the Chase: How Matrix Metalloproteinase-2 Activity Controls Breast-Cancer-to-Bone Metastasis

Bone metastatic breast cancer is currently incurable and will be evident in more than 70% of patients that succumb to the disease. Understanding the factors that contribute to the progression and metastasis of breast cancer can reveal therapeutic opportunities. Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes whose role in cancer has been widely documented. They are capable of contributing to every step of the metastatic cascade, but enthusiasm for the use of MMP inhibition as a therapeutic approach has been dampened by the disappointing results of clinical trials conducted more than 20 years ago. Since the trials, our knowledge of MMP biology has expanded greatly. Combined with advances in the selective targeting of individual MMPs and the specific delivery of therapeutics to the tumor microenvironment, we may be on the verge of finally realizing the promise of MMP inhibition as a treatment strategy. Here, as a case in point, we focus specifically on MMP-2 as an example to show how it can contribute to each stage of breast-cancer-to-bone metastasis and also discuss novel approaches for the selective targeting of MMP-2 in the setting of the bone-cancer microenvironment.

A history of exploring cancer in context

The concept that progression of cancer is regulated by interactions of cancer cells with their microenvironment was postulated by Stephen Paget over a century ago. Contemporary tumour microenvironment (TME) research focuses on the identification of tumour-interacting microenvironmental constituents, such as resident or infiltrating non-tumour cells, soluble factors and extracellular matrix components, and the large variety of mechanisms by which these constituents regulate and shape the malignant phenotype of tumour cells. In this Timeline article, we review the developmental phases of the TME paradigm since its initial description. While illuminating controversies, we discuss the importance of interactions between various microenvironmental components and tumour cells and provide an overview and assessment of therapeutic opportunities and modalities by which the TME can be targeted.

Emerging and Established Models of Bone Metastasis

Metastasis is the leading cause of cancer-related death and drives patient morbidity as well as healthcare costs. Bone is the primary site of metastasis for several cancers—breast and prostate cancers in particular. Efforts to treat bone metastases have been stymied by a lack of models to study the progression, cellular players, and signaling pathways driving bone metastasis. In this review, we examine newly described and classic models of bone metastasis. Through the use of current in vivo, microfluidic, and in silico computational bone metastasis models we may eventually understand how cells escape the primary tumor and how these circulating tumor cells then home to and colonize the bone marrow. Further, future models may uncover how cells enter and then escape dormancy to develop into overt metastases. Recreating the metastatic process will lead to the discovery of therapeutic targets for disrupting and treating bone metastasis.

Modeling treatment-dependent glioma growth including a dormant tumor cell subpopulation

Background

Tumors comprise a variety of specialized cell phenotypes adapted to different ecological niches that massively influence the tumor growth and its response to treatment.

Methods

In the background of glioblastoma multiforme, a highly malignant brain tumor, we consider a rapid proliferating phenotype that appears susceptible to treatment, and a dormant phenotype which lacks this pronounced proliferative ability and is not affected by standard therapeutic strategies. To gain insight in the dynamically changing proportions of different tumor cell phenotypes under different treatment conditions, we develop a mathematical model and underline our assumptions with experimental data.

Results

We show that both cell phenotypes contribute to the distinct composition of the tumor, especially in cycling low and high dose treatment, and therefore may influence the tumor growth in a phenotype specific way.

Conclusion

Our model of the dynamic proportions of dormant and rapidly growing glioblastoma cells in different therapy settings suggests that phenotypically different cells should be considered to plan dose and duration of treatment schedules.

Relationship between infiltrating lymphocytes in cancerous ascites and dysfunction of Cajal mesenchymal cells in the small intestine

Malignant ascites changes the microenvironment of the peritoneal cavity and damages abdominal functional host cells such as interstitial cells of Cajal (ICC), causing gastrointestinal dysfunction and poor prognosis. Besides tumor cells, malignant ascites contains large numbers of lymphocytes and macrophagocytes. These inflammatory cells act as a 'double arrow' and it is not clear whether they cause injury to ICCs. Our study demonstrates the presence of T lymphocytes in malignant ascites and shows that these cells may have a critical role in inducing damage to ICC via Caspases and Fas/FasL. These inflammatory cells were contributory to gastric dysfunction in our GI tumor-induced ascites mouse models.

Chemotherapy-induced metastasis: mechanisms and translational opportunities

Tumors often overcome the cytotoxic effects of chemotherapy through either acquired or environment-mediated drug resistance. In addition, signals from the microenvironment obfuscate the beneficial effects of chemotherapy and may facilitate progression and metastatic dissemination. Seminal mediators in chemotherapy-induced metastasis appear to be a wide range of hematopoietic, mesenchymal and immune progenitor cells, originating from the bone marrow. The actual purpose of these cells is to orchestrate the repair response to the cytotoxic damage of chemotherapy. However, these repair responses are exploited by tumor cells at every step of the metastatic cascade, ranging from tumor cell invasion, intravasation and hematogenous dissemination to extravasation and effective colonization at the metastatic site. A better understanding of the mechanistic underpinnings of chemotherapy-induced metastasis will allow us to better predict which patients are more likely to exhibit pro-metastatic responses to chemotherapy and will help develop new therapeutic strategies to neutralize chemotherapy-driven prometastatic changes.

Autofluorescence imaging identifies tumor cell-cycle status on a single-cell level

The goal of this study is to validate fluorescence intensity and lifetime imaging of metabolic co-enzymes NAD(P)H and FAD (optical metabolic imaging, or OMI) as a method to quantify cell-cycle status of tumor cells. Heterogeneity in tumor cell-cycle status (e. g. proliferation, quiescence, apoptosis) increases drug resistance and tumor recurrence. Cell-cycle status is closely linked to cellular metabolism. Thus, this study applies cell-level metabolic imaging to distinguish proliferating, quiescent, and apoptotic populations. Two-photon microscopy and time-correlated single photon counting are used to measure optical redox ratio (NAD(P)H fluorescence intensity divided by FAD intensity), NAD(P)H and FAD fluorescence lifetime parameters. Redox ratio, NAD(P)H and FAD lifetime parameters alone exhibit significant differences (p<0.05) between population means. To improve separation between populations, linear combination models derived from partial least squares - discriminant analysis (PLS-DA) are used to exploit all measurements together. Leave-one-out cross validation of the model yielded high classification accuracies (92.4 and 90.1 % for two and three populations, respectively). OMI and PLS-DA also identifies each sub-population within heterogeneous samples. These results establish single-cell analysis with OMI and PLS-DA as a label-free method to distinguish cell-cycle status within intact samples. This approach could be used to incorporate cell-level tumor heterogeneity in cancer drug development.

Cancer cell dormancy: mechanisms and implications of cancer recurrence and metastasis

More recently, disease metastasis and relapse in many cancer patients several years (even some decades) after surgical remission are regarded as tumor dormancy. However, the knowledge of this phenomenon is cripplingly limited. Substantial quantities of reviews have summarized three main potential models that can be put forth to explain such process, including angiogenic dormancy, immunologic dormancy, and cellular dormancy. In this review, newly uncovered mechanisms governing cancer cell dormancy are discussed, with an emphasis on the cross talk between dormant cancer cells and their microenvironments. In addition, potential mechanisms of reactivation of these dormant cells in certain anatomic sites including lymph nodes and bone marrow are discussed. Molecular mechanism of cellular dormancy in head and neck cancer is also involved.

Hypoxia and Bone Metastatic Disease

PURPOSE OF REVIEW

This review highlights our current knowledge of oxygen tensions in the bone marrow, and how low oxygen tensions (hypoxia) regulate tumor metastasis to and colonization of the bone marrow.

RECENT FINDINGS

The bone marrow is a relatively hypoxic microenvironment, but oxygen tensions fluctuate throughout the marrow cavity and across the endosteal and periosteal surfaces. Recent advances in imaging have made it possible to better characterize these fluctuations in bone oxygenation, but technical challenges remain. We have compiled evidence from multiple groups that suggests that hypoxia or hypoxia inducible factor (HIF) signaling may induce spontaneous metastasis to the bone and promote tumor colonization of bone, particularly in the case of breast cancer dissemination to the bone marrow. We are beginning to understand oxygenation patterns within the bone compartment and the role for hypoxia and HIF signaling in tumor cell dissemination to the bone marrow, but further studies are warranted.