Do we need to redefine a cancer metastasis and staging definitions?

Connexins in Cancer, the Possible Role of Connexin46 as a Cancer Stem Cell-Determining Protein

Cancer is a widespread and incurable disease caused by genetic mutations, leading to uncontrolled cell proliferation and metastasis. Connexins (Cx) are transmembrane proteins that facilitate intercellular communication via hemichannels and gap junction channels. Among them, Cx46 is found mostly in the eye lens. However, in pathological conditions, Cx46 has been observed in various types of cancers, such as glioblastoma, melanoma, and breast cancer. It has been demonstrated that elevated Cx46 levels in breast cancer contribute to cellular resistance to hypoxia, and it is an enhancer of cancer aggressiveness supporting a pro-tumoral role. Accordingly, Cx46 is associated with an increase in cancer stem cell phenotype. These cells display radio- and chemoresistance, high proliferative abilities, self-renewal, and differentiation capacities. This review aims to consolidate the knowledge of the relationship between Cx46, its role in forming hemichannels and gap junctions, and its connection with cancer and cancer stem cells.

Targeting tumor innervation: premises, promises, and challenges

A high intratumoral nerve density is correlated with poor survival, high metastasis, and high recurrence across multiple solid tumor types. Recent research has revealed that cancer cells release diverse neurotrophic factors and exosomes to promote tumor innervation, in addition, infiltrating nerves can also mediate multiple tumor biological processes via exosomes and neurotransmitters. In this review, through seminal studies establishing tumor innervation, we discuss the communication between peripheral nerves and tumor cells in the tumor microenvironment (TME), and revealed the nerve-tumor regulation mechanisms on oncogenic process, angiogenesis, lymphangiogenesis, and immunity. Finally, we discussed the promising directions of ‘old drugs newly used’ to target TME communication and clarified a new line to prevent tumor malignant capacity.

Nerve input to tumours: Pathophysiological consequences of a dynamic relationship

It is well known that tumours arising in different organs are innervated and that 'perineural invasion' (cancer cells escaping from the tumour by following the nerve trunk) is a negative prognostic factor. More surprisingly, increasing evidence suggests that the nerves can provide active inputs to tumours and there is two-way communication between nerves and cancer cells within the tumour microenvironment. Cells of the immune system also interact with the nerves and cancer cells. Thus, the nerve connections can exert significant control over cancer progression and modulating these (physically or chemically) can affect significantly the cancer process. Nerve inputs to tumours are derived mainly from the sympathetic (adrenergic) and the parasympathetic (cholinergic) systems, which are interactive. An important component of the latter is the vagus nerve, the largest of the cranial nerves. Here, we present a two-part review of the nerve inputs to tumours and their effects on tumorigenesis. First, we review briefly some relevant general issues including ultrastructural aspects, stemness, interactions between neurones and primary tumours, and communication between neurones and metastasizing tumour cells. Ultrastructural characteristics include synaptic vesicles, tumour microtubes and gap junctions enabling formation of cellular networks. Second, we evaluate the pathophysiology of the nerve input to five major carcinomas: cancers of prostate, stomach, colon, lung and pancreas. For each cancer, we present (i) the nerve inputs normally present in the cancer organ and (ii) how these interact and influence the cancer process. The best clinical evidence for the role of nerves in promoting tumorigenesis comes from prostate cancer patients where metastatic progression has been shown to be suppressed significantly in cases of spinal cord injury. The balance of the sympathetic and parasympathetic contributions to early versus late tumorigenesis varies amongst the different cancers. Different branches of the vagus provide functional inputs to several of the carcinomas and, in two-way interaction with the sympathetic nervous system, affect different stages of the cancer process. Overall, the impact of the vagus nerve can be 'direct' or 'indirect'. Directly, the effect of the vagus is primarily to promote tumorigenesis and this is mediated through cholinergic receptor mechanisms. Indirectly, pro- and anti-tumour effects can occur by stimulation or inhibition of the sympathetic nervous system, respectively. Less well understood are the 'indirect' anti-tumour effect of the vagus nerve via immunomodulation/inflammation, and the role of sensory innervation. A frequent occurrence in the nerve-tumour interactions is the presence of positive feedback driven by agents like nerve growth factor. We conclude that the nerve inputs to tumours can actively and dynamically impact upon cancer progression and are open to clinical exploitation.

Riluzole: Anti-invasive effects on rat prostate cancer cells under normoxic and hypoxic conditions

Anti-invasive effects of riluzole and ranolazine, a neuro-protectant and an anti-anginal drug, respectively, on Mat-LyLu rat prostate cancer (PCa) cells were tested in vitro (a) at non-toxic doses and (b) under both normoxic and hypoxic conditions, the latter common to growing tumours. Tetrodotoxin (TTX) was used as a positive control. Hypoxia had no effect on cell viability but reduced growth at 48 hours. Riluzole (5 μmol/L) or ranolazine (20 μmol/L) had no effect on cell viability or growth under normoxia or hypoxia over 24 hours. Matrigel invasion was not affected by hypoxia but inhibited by TTX, ranolazine and riluzole under a range of conditions. The expression of Nav1.7 mRNA, the prevailing, pro-invasive voltage-gated sodium channel α-subunit (VGSCα), was up-regulated by hypoxia. Riluzole had no effect on Nav1.7 mRNA expression in normoxia but significantly reduced it in hypoxia. VGSCα protein expression in plasma membrane was reduced in hypoxia; riluzole increased it but only under hypoxia. It was concluded (a) that riluzole and ranolazine have anti-invasive effects on rat PCa cells and (b) that Nav1.7 mRNA and protein expression can be modulated by riluzole under hypoxia. Overall, therefore, riluzole and ranolazine may ultimately be "repurposed" as anti-metastatic drugs against PCa.

Framing cancer progression: influence of the organ- and tumour-specific matrisome

The extracellular matrix (ECM) plays a crucial role in regulating organ homeostasis. It provides mechanical and biochemical cues directing cellular behaviour and, therefore, has control over the progression of diseases such as cancer. Recent efforts have greatly enhanced our knowledge of the protein composition of the ECM and its regulators, the so-called matrisome, in healthy and cancerous tissues; yet, an overview of the common signatures and organ-specific ECM in cancer is missing. Here, we address this by taking a detailed approach to review why cancer grows in certain organs, and focus on the influence of the matrisome at primary and metastatic tumour sites. Our in-depth and comprehensive review of the current literature and general understanding identifies important commonalities and distinctions, providing insight into the biology of metastasis, which could pave the way to improve future diagnostics and therapies.

E-Cadherin Downregulation is Mediated by Promoter Methylation in Canine Prostate Cancer

E-cadherin is a transmembrane glycoprotein responsible for cell-to-cell adhesion, and its loss has been associated with metastasis development. Although E-cadherin downregulation was previously reported in canine prostate cancer (PC), the mechanism involved in this process is unclear. It is well established that dogs, besides humans, spontaneously develop PC with high frequency; therefore, canine PC is an interesting model to study human PC. In human PC, CDH1 methylation has been associated with E-cadherin downregulation. However, no previous studies have described the methylation pattern of CDH1 promoter in canine PC. Herein, we evaluated the E-cadherin protein and gene expression in canine PC compared to normal tissues. DNA methylation pattern was investigated as a regulatory mechanism of CDH1 silencing. Our cohort is composed of 20 normal prostates, 20 proliferative inflammatory atrophy (PIA) lesions, 20 PC, and 11 metastases from 60 dogs. The E-cadherin protein expression was assessed by immunohistochemistry and western blotting and gene expression by qPCR. Bisulfite- pyrosequencing assay was performed to investigate the CDH1 promoter methylation pattern. Membranous E-cadherin expression was observed in all prostatic tissues. A higher number of E-cadherin negative cells was detected more frequently in PC compared to normal and PIA samples. High-grade PC showed a diffuse membranous positive immunostaining. Furthermore, PC patients with a higher number of E-cadherin negative cells presented shorter survival time and higher Gleason scores. Western blotting and qPCR assays confirmed the immunohistochemical results, showing lower E-cadherin protein and gene expression levels in PC compared to normal samples. We identified CDH1 promoter hypermethylation in PIA and PC samples. An in vitro assay with two canine prostate cancer cells (PC1 and PC2 cell lines) was performed to confirm the methylation as a regulatory mechanism of E-cadherin expression. PC1 cell line presented CDH1 hypermethylation and after 5-Aza-dC treatment, a decreased CDH1 methylation and increased gene expression levels were observed. Positive E-cadherin cells were massively found in metastases (mean of 90.6%). In conclusion, low levels of E-cadherin protein, gene downregulation and CDH1 hypermethylation was detected in canine PC. However, in metastatic foci occur E-cadherin re-expression confirming its relevance in these processes.

The role of vitamin D in hepatic metastases from colorectal cancer

Colorectal cancer (CRC) represents a significant health burden worldwide, comprising approximately 10% of annual cancer cases globally. Hepatic metastases are the most common site of CRC metastasis, and are the leading cause of death in CRC patients. There is strong epidemiologic evidence for an inverse association between vitamin D status and risk of CRC; however, the role of vitamin D in the natural history of liver metastases has not yet been investigated. Several researchers have proposed hallmarks of metastases; crucially, metastases can be blocked by interrupting just one rate-limiting step. Vitamin D status has been implicated in each proposed hallmark of metastasis. The aim of this review is to examine the potential role for vitamin D in reducing the development of hepatic metastases from CRC and outline the candidate mechanisms by which vitamin D may mediate these effects. The results of ongoing randomised intervention trials are eagerly awaited to determine whether addressing vitamin D insufficiency in CRC patients could reduce the occurrence of liver metastases, and the consequent morbidity and mortality.

Coexisting and possible primary extra-gastrointestinal stromal tumors of the pancreas and liver: A single case report

Gastrointestinal stromal tumors (GIST) are mesenchymal neoplasms of the gastrointestinal tract (GI) that are defined, in part, by the expression of CD117, a c-Kit proto-oncogene protein. GISTs emerge outside of the GI at a very low frequency, typically in a single organ or location. GISTs that occasionally emerge outside of the GI are classified as extra-gastrointestinal stromal tumors (EGIST). The present study reports an extremely rare case of EGIST detected in the pancreas and the liver. The pancreatic and liver tumors were 4.5×2.5 cm and 2.0×1.5 cm in size, respectively. Both tumors consisted of CD117-positive spindle cells with a similar mitotic rate of 1–2 per 50 high power fields. The pancreatic and the hepatic EGISTs were at a low risk of malignancy, and both tumors were proposed to be primary stromal tumors. To the best of our knowledge, this is the first report of likely primary EGIST identified in the pancreas and liver of the same patient.

Filamin A phosphorylation by Akt promotes cell migration in response to arsenic

We had previously reported that trivalent arsenic (As³⁺), a well-known environmental carcinogen, induces phosphorylation of several putative Akt substrates. In the present report, we characterized one of these substrates by immunoprecipitation and proteomics analysis. The results indicate that a cytoskeleton remodeling protein, filamin A, with a molecular weight around 280 kDa, is phosphorylated by Akt in HEK-293 cells treated with As³⁺, which was also confirmed in human bronchial epithelial cell line, BEAS-2B cells. Additional biochemical and biological studies revealed that serine 2152 (S2152) of filamin A is phosphorylated by activated Akt in the cells treated with As³⁺. To further confirm the importance of Akt-dependent filamin A S2152 phosphorylation in As³⁺-induced cell migration, we over-expressed either wild type filamin A or the mutated filamin A in which the S2152 was substituted with alanine (S2152A). The capability of cell migration was reduced significantly in the cells expressing the mutated filamin A (S2152A). Clinically, we found that increased expression of filamin A predicts poorer overall survival of the lung cancer patients with adenocarcinoma. Thus, these data suggest that Akt dependent filamin A phosphorylation is one of the key events in mediating As³⁺-induced carcinogenesis. Antagonizing Akt signaling can ameliorate As³⁺-induced filamin A phosphorylation and cell migration, which may serve as a molecular targeting strategy for malignancies associated with environmental As³⁺ exposure.

Humanised xenograft models of bone metastasis revisited: novel insights into species-specific mechanisms of cancer cell osteotropism

The determinants and key mechanisms of cancer cell osteotropism have not been identified, mainly due to the lack of reproducible animal models representing the biological, genetic and clinical features seen in humans. An ideal model should be capable of recapitulating as many steps of the metastatic cascade as possible, thus facilitating the development of prognostic markers and novel therapeutic strategies. Most animal models of bone metastasis still have to be derived experimentally as most syngeneic and transgeneic approaches do not provide a robust skeletal phenotype and do not recapitulate the biological processes seen in humans. The xenotransplantation of human cancer cells or tumour tissue into immunocompromised murine hosts provides the possibility to simulate early and late stages of the human disease. Human bone or tissue-engineered human bone constructs can be implanted into the animal to recapitulate more subtle, species-specific aspects of the mutual interaction between human cancer cells and the human bone microenvironment. Moreover, the replication of the entire "organ" bone makes it possible to analyse the interaction between cancer cells and the haematopoietic niche and to confer at least a partial human immunity to the murine host. This process of humanisation is facilitated by novel immunocompromised mouse strains that allow a high engraftment rate of human cells or tissue. These humanised xenograft models provide an important research tool to study human biological processes of bone metastasis.

Breast cancer metastasis: issues for the personalization of its prevention and treatment

Despite important progress in adjuvant and neoadjuvant therapies, metastatic disease often develops in breast cancer patients and remains the leading cause of their deaths. For patients with established metastatic disease, therapy is palliative, with few breaks and with mounting adverse effects. Many have hypothesized that a personalized or precision approach (the terms are used interchangeably) to cancer therapy, in which treatment is based on the individual characteristics of each patient, will provide better outcomes. Here, we discuss the molecular basis of breast cancer metastasis and the challenges in personalization of treatment. The instability of metastatic tumors remains a leading obstacle to personalization, because information from a patient's primary tumor may not accurately reflect the metastasis, and one metastasis may vary from another. Furthermore, the variable presence of tumor subpopulations, such as stem cells and dormant cells, may increase the complexity of the targeted treatments needed. Although molecular signatures and circulating biomarkers have been identified in breast cancer, there is lack of validated predictive molecular markers to optimize treatment choices for either prevention or treatment of metastatic disease. Finally, to maximize the information that can be obtained, increased attention to clinical trial design in the metastasis preventive setting is needed.

Detection of mammaglogin A in blood from breast cancer patients, before and after treatment, using a one-tube nested PCR protocol. Association with the absence of tumor estrogen receptors

OBJECTIVE

A one-tube nested RT-PCR protocol was set up and used to detect mammaglobin A (MGA) expression in blood samples from breast cancer patients. The correlation of MGA detection with prognostic factors was analyzed.

DESIGN AND METHODS

Total RNA from nucleated blood cells was extracted from 65 breast cancer patients (before surgery and after the treatments) and 18 healthy subjects and used to detect MGA expression by a modified nested RT-PCR.

RESULTS

MGA expression was detected in 38.4% of patients before surgery, and in 50% and 36.8% of post-treatment samples from patients that expressed MGA or were MGA negative before surgery, respectively. MGA detection was associated with the absence of tumor estrogen receptors (p=0.004).

CONCLUSIONS

MGA detection by the modified nested RT-PCR is a specific marker for circulating tumor cells in patients with breast carcinoma and a negative prognostic factor for the disease.

Metastasis suppressor genes at the interface between the environment and tumor cell growth

The molecular mechanisms and genetic programs required for cancer metastasis are sometimes overlapping, but components are clearly distinct from those promoting growth of a primary tumor. Every sequential, rate-limiting step in the sequence of events leading to metastasis requires coordinated expression of multiple genes, necessary signaling events, and favorable environmental conditions or the ability to escape negative selection pressures. Metastasis suppressors are molecules that inhibit the process of metastasis without preventing growth of the primary tumor. The cellular processes regulated by metastasis suppressors are diverse and function at every step in the metastatic cascade. As we gain knowledge into the molecular mechanisms of metastasis suppressors and cofactors with which they interact, we learn more about the process, including appreciation that some are potential targets for therapy of metastasis, the most lethal aspect of cancer. Until now, metastasis suppressors have been described largely by their function. With greater appreciation of their biochemical mechanisms of action, the importance of context is increasingly recognized especially since tumor cells exist in myriad microenvironments. In this chapter, we assemble the evidence that selected molecules are indeed suppressors of metastasis, collate the data defining the biochemical mechanisms of action, and glean insights regarding how metastasis suppressors regulate tumor cell communication to-from microenvironments.

Specificity and robustness of the mammalian MAPK-IEG network

The mitogen-activated protein kinase cascade is a conserved signal transduction pathway found in organisms of complexity spanning from yeast to humans. In many mammalian tissue types, this pathway can correctly transduce signals from different extracellular messengers, leading to specific and often mutually exclusive cellular responses. The transduced signal is tuned by a complicated set of positive and negative feedback control mechanisms and fed into a downstream gene expression network. This network, based on the immediate early gene system, has two possible, mutually exclusive outcomes. Using a mathematical model, we study how different stimuli lead to different temporal signal structure. Further, we investigate how each of the feedback controls contributes to the overall specificity of the gene expression output, and hypothesize that the complicated nature of the mammalian mitogen-activated protein kinase pathway results in a system able to robustly identify and transduce the proper signal without investing in two completely separate signal cascades. Finally, we quantify the role of the RKIP protein in shaping the signal, and propose a novel mechanism of its involvement in cancer metastasis.

Dietary stearate reduces human breast cancer metastasis burden in athymic nude mice

Stearate is an 18-carbon saturated fatty acid found in many foods in the western diet, including beef and chocolate. Stearate has been shown to have anti-cancer properties during early stages of neoplastic progression. However, previous studies have not investigated the effect of dietary stearate on breast cancer metastasis. In this study, we present evidence that exogenously supplied dietary stearate dramatically reduces the size of tumors that formed from injected human breast cancer cells within the mammary fat pads of athymic nude mice by approximately 50% and partially inhibits breast cancer cell metastasis burden in the lungs in this mouse model system. This metastatic inhibition appears to be independent of primary tumor size, as stearate fed animals that had primary tumors comparable in size to littermates fed either a safflower oil enriched diet or a low fat diet had reduced lung metastasis. Also stearate fed mice sub-groups had different primary tumor sizes but no difference in metastasis. This anti-metastasis effect may be due, at least in part, to the ability of stearate to induce apoptosis in these human breast cancer cells. Overall, this study suggests the possibility of dietary manipulation with selected long-chain saturated fatty acids such as stearate as a potential adjuvant therapeutic strategy for breast cancer patients wishing to maximize the suppression of metastatic disease.

Societal interactions in ovarian cancer metastasis: a quorum-sensing hypothesis

The biochemical and biological mechanisms metastatic cancer cells use to function as communities and thwart internal and external growth control mechanisms remain undefined. In this work, we present the hypothesis that cancer cells may use a Quorum-Sensing mechanism to regulate multicellular functions and control steps in metastatic colonization. Quorum sensing is a bacterial cell-cell communication process used to track increasing cell-population density and, in response to changes in cell number, coordinate gene expression and behavior on a community-wide scale. Important parallels between the behavior of societies of bacterial cells and societies of malignant cancer cells exist in the bacterial literature. Of relevance to metastasis is the finding that pathogenic bacteria use quorum sensing to determine when their population numbers are high enough to collectively form biofilms in or on host organisms. Biofilms are complex, heterogeneous communities of bacterial cells encased within an extracellular matrix attached to a solid surface. Biofilms exacerbate disease and are refractory to a battery of therapies. We suggest that the quorum-sensing-controlled bacterial biofilm formation process closely parallels the steps in metastatic colonization. Cells migrate toward/on target surfaces (organ-specific homing), show cell-cell and cell-matrix interactions (tumor cell-stromal cell crosstalk), remain subclinical until they can mount an effective attack (dormancy), form complex structures with channels for nutrient flow (vascularized lesions), and contain resistant cells which can cause disease recurrence (persistors). Using ovarian cancer as an example, we present data supporting the connection between metastatic colonization and quorum sensing and discuss the implications for understanding and controlling metastasis formation.

BRMS1 suppresses breast cancer experimental metastasis to multiple organs by inhibiting several steps of the metastatic process

Breast cancer metastasis suppressor 1 (BRMS1) inhibits formation of macroscopic lung metastases in breast, ovary, and melanoma xenograft models. Because it is unclear which step(s) of the metastatic cascade are affected by BRMS1, the major aim of this study was to determine when and how BRMS1 acts to suppress metastasis. We also examined whether BRMS1 expression globally blocks metastasis or selectively inhibits metastatic outgrowths in specific tissues. Metastatic human breast carcinoma cell lines MDA-MB-231 and -435 expressing enhanced green fluorescent protein (GFP; 231 GFP and 435 GFP) and cell lines transduced with the BRMS1 gene (231 GFP-BRMS1 and 435 GFP-BRMS1) were injected into the left cardiac ventricle to achieve the widest possible cellular distribution, by minimizing first-pass clearance in the lungs. Compared with parental cells, BRMS1-expressing clones formed significantly fewer metastases in all organs tested. When cells were injected directly into the vasculature, fewer of the BRMS1-expressing cells reached lungs or bone compared with parental cells, suggesting that restoration of BRMS1 expression increased cell death during transit. Susceptibility to anoikis was verified in vitro by demonstrating decreased survival on poly-hydroxyethyl methacrylate-coated dishes. Most of the BRMS1-expressing cells reaching secondary sites failed to proliferate, suggesting that BRMS1 also inhibits colonization. Coupled with previous reports showing modest effects of BRMS1 on adhesion and invasion, our results indicate that BRMS1 inhibits metastases in multiple organs by blocking several steps in the metastatic cascade.

Metastasis suppressors and the tumor microenvironment

The most dangerous attribute of cancer cells is their ability to metastasize. Throughout the process of metastasis, tumor cells interact with other tumor cells, host cells and extracellular molecules. This brief review explores how a new class of molecules – metastasis suppressors – regulate tumor cell–microenvironmental interactions. Data are presented which demonstrate that metastasis suppressors act at multiple steps of the metastatic cascade. A brief discussion for how metastasis suppressor regulation of cellular interactions might be exploited is presented.

Metastasis suppressors and their roles in breast carcinoma

Metastasis remains the most deadly aspect of cancer and still evades direct treatment. Clinically and experimentally, primary tumor development and metastasis are distinct processes-locally growing tumors can progress without the development of metastases. The discovery of endogenous molecules that exclusively inhibit metastasis suggests that metastasis is an amenable therapeutic target. By definition, metastasis suppressors inhibit metastasis without inhibiting tumorigenicity and are thus distinct from tumor suppressors. As the biology underlying functional mechanisms of metastasis suppressors becomes clearer, it is evident that metastasis suppressors could be harnessed as direct drug targets, prognostic markers, and to understand the fundamental biology of the metastatic process. Metastasis suppressors vary widely in their cellular localization: they are found in every cellular compartment and some are secreted. In general, metastasis suppressors appear to regulate selectively how cells respond to exogenous signals, by affecting signaling cascades which regulate downstream gene expression. This review briefly summarizes current functional and biochemical data on metastasis suppressors implicated in breast cancer. We also present a schematic integrating known mechanisms for these metastasis suppressors highlighting potential targets for therapeutic intervention.