Adenosine down-regulates the surface expression of dipeptidyl peptidase IV on HT-29 human colorectal carcinoma cells: implications for cancer cell behavior

Apigenin directly interacts with and inhibits topoisomerase 1 to upregulate CD26/DPP4 on colorectal carcinoma cells

Introduction: CD26/dipeptidyl peptidase IV (DPP4) is a cell-surface glycoprotein present on most epithelial cells that modulates the local response to external signals. We have previously shown that the dietary flavone apigenin (4',5,7-trihydroxyflavone) upregulates cell-surface CD26/DPP4 on human colorectal carcinoma (CRC) cells and regulates its activities. We observed a unique synergistic interaction with the CRC chemotherapeutic agent irinotecan, which through its metabolite SN38 elevates CD26 at doses that are sub-cytotoxic. As SN38 interacts with topoisomerase 1 (Topo1) we evaluated whether apigenin influences Topo1 activity. Methods: We used a radioimmunoassay to selectively measure CD26 at the cell surface of HT-29 cells following various treatments. Topoisomerase 1 mRNA expression was measured by q-RT-PCR and protein abundance by western blot analysis. Direct inhibition of topoisomerase activity was measured using an assay of DNA supercoil relaxation with recombinant human Topo1. The role of Topo1 in the effect of apigenin was shown both pharmacologically and by siRNA silencing of Topo1. Molecular docking analysis was done with SBD computational software using the CDOCKER algorithm. Results: The interplay between apigenin and irinotecan was not observed when apigenin was combined with other chemotherapeutic drugs including the topoisomerase 2 inhibitors doxorubicin or etoposide. There was no enhancement of irinotecan action if apigenin was replaced with its hydroxylated metabolite luteolin (3',4',5,7-tetrahydroxyflavone) or emodin (6-methyl-1,3,8-trihydroxyanthraquinone), which is an inhibitor of the principal kinase target of apigenin, casein kinase 2 (CK2). Apigenin did not alter Topo1 mRNA expression, but siRNA knockdown of functional Topo1 eliminated the effect of apigenin and itself increased CD26 levels. Apigenin inhibited Topo1 activity in intact HT-29 cells and showed comparable inhibition of purified recombinant human Topo1 enzyme activity to that of SN-38, the active metabolite of irinotecan. Apigenin fits into the complex of Topo1 with DNA to directly inhibit Topo1 enzyme activity. Discussion: We conclude that apigenin has a unique fit into the Topo1-DNA functional complex that leads to direct inhibition of Topo1 activity, and suggest that this is the basis for the exceptional interaction with the CRC drug irinotecan. A combined action of these two agents may therefore exert a role to limit local signals that facilitate tumour progression.

EGFR-targeted bacteriophage lambda penetrates model stromal and colorectal carcinoma tissues, is taken up into carcinoma cells, and interferes with 3-dimensional tumor formation

Introduction

Colorectal cancer and other adult solid cancers pose a significant challenge for successful treatment because the tumor microenvironment both hinders the action of conventional therapeutics and suppresses the immune activities of infiltrating leukocytes. The immune suppression is largely the effect of enhanced local mediators such as purine nucleosides and eicosanoids. Genetic approaches have the promise of interfering with these mechanisms of local immunosuppression to allow both intrinsic and therapeutic immunological anticancer processes. Bacterial phages offer a novel means of enabling access into tissues for therapeutic genetic manipulations.

Methods

We generated spheroids of fibroblastic and CRC cancer cells to model the 3-dimensional stromal and parenchymal components of colorectal tumours. We used these to examine the access and effects of both wildtype (WT) and epidermal growth factor (EGF)-presenting bacteriophage λ (WT- λ and EGF-λ) as a means of delivery of targeted genetic interventions in solid cancers. We used both confocal microscopy of spheroids exposed to AF488-tagged phages, and the recovery of viable phages as measured by plaque-forming assays to evaluate access; and measures of mitochondrial enzyme activity and cellular ATP to evaluate the outcome on the constituent cells.

Results

Using flourescence-tagged derivatives of these bacteriophages (AF488-WT-λ and AF488-EGF-λ) we showed that phage entry into these tumour microenvironments was possible and that the EGF ligand enabled efficient and persistent uptake into the cancer cell mass. EGF-λ became localized in the intracellular portion of cancer cells and was subjected to subsequent cellular processing. The targeted λ phage had no independent effect upon mature tumour spheroids, but interfered with the early formation and growth of cancer tissues without the need for addition of a toxic payload, suggesting that it might have beneficial effects by itself in addition to any genetic intervention delivered to the tumour. Interference with spheroid formation persisted over the duration of culture.

Discussion

We conclude that targeted phage technology is a feasible strategy to facilitate delivery into colorectal cancer tumour tissue (and by extension other solid carcinomas) and provides an appropriate delivery vehicle for a gene therapeutic that can reduce local immunosuppression and/or deliver an additional direct anticancer activity.

Seeding metastases: The role and clinical utility of circulating tumour cells

Peripheral human blood is a readily-accessible source of patient material in which circulating tumour cells (CTCs) can be found. Their isolation and characterization holds the potential to provide prognostic value for various solid cancers. Enumeration of CTCs from blood is becoming a common practice in informing prognosis and may guide therapy decisions. It is further recognized that enumeration alone does not capture perspective on the heterogeneity of tumours and varying functional abilities of the CTCs to interact with the secondary microenvironment. Characterizing the isolated CTCs further, in particular assessing their functional abilities, can track molecular changes in the disease progress. As a step towards identifying a suite of functional features of CTCs that could aid in clinical decisions, developing a CTC isolation technique based on extracellular matrix (ECM) interactions may provide a more solid foundation for isolating the cells of interest. Techniques based on size, charge, density, and single biomarkers are not sufficient as they underutilize other characteristics of cancer cells. The ability of cancer cells to interact with ECM proteins presents an opportunity to utilize their full character in capturing, and also allows assessment of the features that reveal how cells might behave at secondary sites during metastasis. This article will review some common techniques and recent advances in CTC capture technologies. It will further explore the heterogeneity of the CTC population, challenges they experience in their metastatic journey, and the advantages of utilizing an ECM-based platform for CTC capture. Lastly, we will discuss how tailored ECM approaches may present an optimal platform to capture an influential heterogeneous population of CTCs.

Does Oral Apigenin Have Real Potential for a Therapeutic Effect in the Context of Human Gastrointestinal and Other Cancers?

Apigenin (4′, 5, 7-trihydroxyflavone) is a plant flavone that has been found to have various actions against cancer cells. We evaluated available evidence to determine whether it is feasible for apigenin to have such effects in human patients.

Apigenin taken orally is systemically absorbed and recirculated by enterohepatic and local intestinal pathways. Its bioavailability is in the region of 30%. Once absorbed from the oral route it reaches maximal circulating concentration (C_max) after a time (T_max) of 0.5–2.5h, with an elimination half-life (T¹/₂) averaging 2.52 ± 0.56h.

Using a circulating concentration for efficacy of 1–5μmol/L as the target, we evaluated data from both human and rodent pharmacokinetic studies to determine if a therapeutic concentration would be feasible. We find that oral intake of dietary materials would require heroic ingestion amounts and is not feasible. However, use of supplements of semi-purified apigenin in capsule form could reach target blood levels using amounts that are within the range currently acceptable for other supplements and medications. Modified formulations or parenteral injection are suitable but may not be necessary.

Further work with direct studies of pharmacokinetics and clinical outcomes are necessary to fully evaluate whether apigenin will contribute to a useful clinical strategy, but given emerging evidence that it may interact beneficially with chemotherapeutic drugs, this is worthy of emphasis. In addition, more effective access to intestinal tissues from the oral route raises the possibility that apigenin may be of particular relevance to gastrointestinal disorders including colorectal cancer.

The mechanism of sitagliptin inhibition of colorectal cancer cell lines' metastatic functionalities

The cell membrane glycoprotein CD26 with peptidase activity (DPP4) and/or its soluble CD26/DPP4 counterpart expression and/or activity are altered in several cancers. Its role in metastasis development was recently highlighted by the discovery of CD26⁺ cancer stem cell subsets and the fact that clinical DPP4 inhibitors showed antimetastatic effects in animal models. Also, diabetic patients treated with the DPP4 inhibitor sitagliptin showed greater overall survival after colorectal or lung cancer surgery than patients under other diabetic therapies. However, the mechanism of action of these inhibitors in this context is unclear. We studied the role of CD26 and its DPP4 enzymatic activity in malignant cell features such as cell-to-cell homotypic aggregation, cancer cell motility, and invasion in a panel of human colorectal cancer (CRC) cell lines, avoiding models that include the physiological role of DPP4 in chemotaxis. Present results indicate that CD26 participates in the induction of cell invasion, motility, and aggregation of CD26-positive CRC cell lines. Moreover, only invasion and motility assays, which are collagen matrix-dependent, showed a decrease upon treatment with the DPP4 inhibitor sitagliptin. Sitagliptin showed opposite effects to those of transforming growth factor-β1 on epithelial-to-mesenchymal transition and cell cycle, but this result does not explain its CD26/DPP4-dependent effect. These results contribute to the elucidation of the molecular mechanisms behind sitagliptin inhibition of metastatic traits. At the same time, this role of sitagliptin may help to define areas of medicine where DPP4 inhibitors might be introduced. However, they also suggest that additional tools against CD26 as a target might be used or developed for metastasis prevention in addition to gliptins.

Apigenin upregulation of CD26/DPPIV on colon epithelial cells requires inhibition of casein kinase 2

CD26/DPPIV is a cell surface glycoprotein found on cells of the intestinal epithelium including those of the colon. We have previously shown that the dietary flavone apigenin (4',5,7-trihydroxyflavone) upregulates CD26/DPPIV on colon cells. Flavonoids such as apigenin interfere with the action of multiple cellular protein kinases and have the capacity to modulate the cell exterior and its ability to interface with the local environment through different signaling pathways. We show here that the ability of apigenin to upregulate CD26/DPPIV is exerted through and requires the activity of casein kinase 2 (CK2). Inhibitors of CK2 that are distinct from apigenin (emodin, 6-methyl-1,3,8-trihydroxyanthraquinone; TBB, 4,5,6,7-tetrabromobenzotriazole; and DRB, 5,6-dichlorobenzimidazole 1-β-D-ribofuranoside) showed a dose-dependent ability to increase CD26/DPPIV and had the same maximal effect when combined with apigenin at submaximal concentrations. Knockdown of CK2 with siRNA abrogated the ability of apigenin to upregulate CD26/DPPIV. Apigenin treatment of cells had no effect on the levels of CK2 protein, consistent with an inhibition of activity of the enzyme. Apigenin's upregulation of CD26/DPPIV in differentiated human colon epithelial cells depends upon inhibition of CK2 activity. This is a key step in enabling apigenin's ability to regulate the functions of intestinal epithelial cells.

Adenosine and adenosine receptors in colorectal cancer

CD39 (nucleoside triphosphate diphosphohydrolase) and Ecto-5-nucleotidase (CD73) have been recognized as important factors mediating various pathological and physiological responses in the tumor microenvironment. Elevated expression of CD73 and CD39 is correlated with the over-production of adenosine in the tumor region. This increase is associated with an immunosuppressive state in the tumor site that enhances various tumor hallmarks such as metastasis, angiogenesis, and cell proliferation. Adenosine promotes these behaviors through interaction with four adenosine receptors, including A3R, A2BR, A2AR, and A1R. Signaling of these receptors reduces the function of immune effector cells and enhances the expansion and function of tumor-associated immune cells. Several studies have been shown the important role of adenosine/CD73/CD39/ARs axis in the immunopathogenesis of colorectal cancer. These findings imply that components of this axis can be considered as a worthy target for colorectal cancer immunotherapy. In this review, we summarized the role of CD73/CD39/adenosine/ARs in the immunopathogenesis of colorectal cancer.

The Adenosine System at the Crossroads of Intestinal Inflammation and Neoplasia

Adenosine is a purine nucleoside, resulting from the degradation of adenosine triphosphate (ATP). Under adverse conditions, including hypoxia, ischemia, inflammation, or cancer, the extracellular levels of adenosine increase significantly. Once released, adenosine activates cellular signaling pathways through the engagement of the four known G-protein-coupled receptors, adenosine A₁ receptor subtype (A₁), A_2A, A_2B, and A₃. These receptors, expressed virtually on all immune cells, mitigate all aspects of immune/inflammatory responses. These immunosuppressive effects contribute to blunt the exuberant inflammatory responses, shielding cells, and tissues from an excessive immune response and immune-mediated damage. However, a prolonged persistence of increased adenosine concentrations can be deleterious, participating in the creation of an immunosuppressed niche, ideal for neoplasia onset and development. Based on this evidence, the present review has been conceived to provide a comprehensive and critical overview of the involvement of adenosine system in shaping the molecular mechanisms underlying the enteric chronic inflammation and in promoting the generation of an immunosuppressive niche useful for the colorectal tumorigenesis.

Targeting immunosuppressive adenosine in cancer

Despite the success of anti-programmed cell death protein 1 (PD1), anti-PD1 ligand 1 (PDL1) and anti-cytotoxic T lymphocyte antigen 4 (CTLA4) therapies in advanced cancer, a considerable proportion of patients remain unresponsive to these treatments (known as innate resistance). In addition, one-third of patients relapse after initial response (known as adaptive resistance), which suggests that multiple non-redundant immunosuppressive mechanisms coexist within the tumour microenvironment. A major immunosuppressive mechanism is the adenosinergic pathway, which now represents an attractive new therapeutic target for cancer therapy. Activation of this pathway occurs within hypoxic tumours, where extracellular adenosine exerts local suppression through tumour-intrinsic and host-mediated mechanisms. Preclinical studies in mice with adenosine receptor antagonists and antibodies have reported favourable antitumour immune responses with some definition of the mechanism of action. Currently, agents targeting the adenosinergic pathway are undergoing first-in-human clinical trials as single agents and in combination with anti-PD1 or anti-PDL1 therapies. In this Review, we describe the complex interplay of adenosine and adenosine receptors in the development of primary tumours and metastases and discuss the merits of targeting one or more components that compose the adenosinergic pathway. We also review the early clinical data relating to therapeutic agents inhibiting the adenosinergic pathway.

Chemotherapeutic agents attenuate CXCL12-mediated migration of colon cancer cells by selecting for CXCR4-negative cells and increasing peptidase CD26

Background

Recurrence of colorectal cancer (CRC) may arise due to the persistence of drug-resistant and cancer-initiating cells that survive exposure to chemotherapy. Proteins responsible for this recurrence include the chemokine receptor CXCR4, which is known to enable CRC metastasis, as well as the cancer-initiating cell marker and peptidase CD26, which terminates activity of its chemokine CXCL12.

Methods

We evaluated the expression and function of CXCR4 and CD26 in colon cancer cell lines and xenografts following treatment with common chemotherapies using radioligand binding, flow cytometry, immunofluorescence, and enzymatic assays.

Results

5-Fluorouracil, oxaliplatin and SN-38 (the active metabolite of irinotecan), as well as cisplatin, methotrexate and vinblastine, each caused decreases in cell-surface CXCR4 and concomitant increases in CD26 on HT-29, T84, HRT-18, SW480 and SW620 CRC cell lines. Flow cytometry indicated that the decline in CXCR4 was associated with a significant loss of CXCR4+/CD26- cells. Elevations in CD26 were paralleled by increases in both the intrinsic dipeptidyl peptidase activity of CD26 as well as its capacity to bind extracellular adenosine deaminase. Orthotopic HT-29 xenografts treated with standard CRC chemotherapeutics 5-fluorouracil, irinotecan, or oxaliplatin showed dramatic increases in CD26 compared to untreated tumors. Consistent with the loss of CXCR4 and gain in CD26, migratory responses to exogenous CXCL12 were eliminated in cells pretreated with cytotoxic agents, although cells retained basal motility. Analysis of cancer-initiating cell CD44 and CD133 subsets revealed drug-dependent responses of CD26/CD44/CD133 populations, suggesting that the benefits of combining standard chemotherapies 5-fluoruracil and oxaliplatin may be derived from their complementary elimination of cell populations.

Conclusion

Our results indicate that conventional anticancer agents may act to inhibit chemokine-mediated migration through eradication of CXCR4+ cells and attenuation of chemokine gradients through elevation of CD26 activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1702-2) contains supplementary material, which is available to authorized users.

Purinergic signalling and cancer

Receptors for extracellular nucleotides are widely expressed by mammalian cells. They mediate a large array of responses ranging from growth stimulation to apoptosis, from chemotaxis to cell differentiation and from nociception to cytokine release, as well as neurotransmission. Pharma industry is involved in the development and clinical testing of drugs selectively targeting the different P1 nucleoside and P2 nucleotide receptor subtypes. As described in detail in the present review, P2 receptors are expressed by all tumours, in some cases to a very high level. Activation or inhibition of selected P2 receptor subtypes brings about cancer cell death or growth inhibition. The field has been largely neglected by current research in oncology, yet the evidence presented in this review, most of which is based on in vitro studies, although with a limited amount from in vivo experiments and human studies, warrants further efforts to explore the therapeutic potential of purinoceptor targeting in cancer.

Immunity, inflammation and cancer: a leading role for adenosine

Cancer is a complex disease that is dictated by both cancer cell-intrinsic and cell-extrinsic processes. Adenosine is an ancient extracellular signalling molecule that can regulate almost all aspects of tissue function. As such, several studies have recently highlighted a crucial role for adenosine signalling in regulating the various aspects of cell-intrinsic and cell-extrinsic processes of cancer development. This Review critically discusses the role of adenosine and its receptors in regulating the complex interplay among immune, inflammatory, endothelial and cancer cells during the course of neoplastic disease.

Dipeptidyl peptidase 10, a novel prognostic marker in colorectal cancer

PURPOSE

The dipeptidyl peptidase IV (DPPIV) gene family exhibits multiple functions and is involved in the pathogenesis of various diseases. It has attracted pharmaceutical interest in the areas of metabolic disorders as well as cancer. However, clinicopathologic significance of DPPIV family in colorectal cancer is not fully understood.

MATERIALS AND METHODS

The clinical relevance of DPPIV and DPP10 expression was determined by immunohistochemical staining, and by assessing its clinicopathologic correlation in 383 colorectal cancer patients with known clinical outcomes.

RESULTS

DPPIV was not expressed in normal colon mucosa, but it showed luminal expression in 52 of the 383 colorectal cancers (13.5%). DPPIV expression in tumors was associated with right-sided location of the colon (p=0.010) and more advanced tumor stage (p=0.045). DPP10 was expressed in normal colonic mucosa, but its expression varied in primary colorectal cancer tissues. Loss of DPP10 expression was found in 11 colorectal cancers (CRCs) (2.9%), and multivariate analysis showed that loss of DPP10 expression was an independent factor for poor patient prognosis (p=0.008).

CONCLUSION

DPP10 may play a role in disease progression of colorectal cancer and loss of DPP10 expression in primary CRC is significantly associated with poor survival outcomes.

Adenosine as an endogenous immunoregulator in cancer pathogenesis: where to go?

Cancer is a chronic disease and its pathogenesis is well correlated with infection and inflammation. Adenosine is a purine nucleoside, which is produced under metabolic stress like hypoxic conditions. Acute or chronic inflammatory conditions lead to the release of precursor adenine nucleotides (adenosine triphosphate (ATP), adenosien diphosphate (ADP) and adenosine monophosphate (AMP)) from cells, which are extracellularly catabolized into adenosine by extracellular ectonucleotidases, i.e., CD39 or nucleoside triphosphate dephosphorylase (NTPD) and CD73 or 5'-ectonucleotidase. It is now well-known that adenosine is secreted by cancer as well as immune cells during tumor pathogenesis under metabolic stress or hypoxia. Once adenosine is released into the extracellular environment, it exerts various immunomodulatory effects via adenosine receptors (A1, A2A, A2B, and A3) expressed on various immune cells (i.e., macrophages, myeloid-derived suppressor cells (MDSCs), natural killer (NK) cells, dendritic cells (DCs), T cells, regulatory T cell (Tregs), etc.), which play very important roles in the pathogenesis of cancer. This review is intended to summarize the role of inflammation and adenosine in the immunopathogenesis of tumor along with regulation of tumor-specific immune response and its modulation as an adjunct approach to tumor immunotherapy.

Differential effect of adenosine receptors on growth of human colon cancer HCT 116 and HT-29 cell lines

The study aimed to evaluate the impact of adenosine receptors (ARs) on human colon tumor cells (HCT 116, HT-29) growth and sensitivity to 5-Fluorouracil (5-FU) an anticancer chemotherapeutic drug. The exposure of cancer cells to a selective A(3)-AR agonist (IB-MECA) resulted in an increase in HT-29 cells number, whereas the number of HCT 116 cells decreased significantly. In the presence of IB-MECA (1 μM) the percentage of apoptotic HT-29 cells significantly decreased, whereas the number of apoptotic and necrotic HCT 116 cells increased by 3- and 2,5-fold, respectively. The application of a selective A(2A)-AR agonist resulted in the increased survival of HCT 116 cells, but not HT-29 cells. The blockade of A(2A)-AR with ZM 241385 (0.1 μM) significantly increased the cytotoxicity of 5-FU (1 μM) in HCT 116 cells but not in HT-29 cells. The suppression of A(3)-AR with MRS 1523 (1 μM) increased the sensitivity of HT-29 cells to 5-FU while response of HCT 116 cells to 5-FU decreased. The growth promoting effect of IB-MECA in HT-29 cells was associated with the decreased intracellular cAMP level, whereas IB-MECA growth inhibitory effect in HCT 116 cells was abolished by okadaic acid (2 nM) indicating the involvement of protein phosphatase PP2A.

CXCR4 in Cancer and Its Regulation by PPARgamma

Chemokines are peptide mediators involved in normal development, hematopoietic and immune regulation, wound healing, and inflammation. Among the chemokines is CXCL12, which binds principally to its receptor CXCR4 and regulates leukocyte precursor homing to bone marrow and other sites. This role of CXCL12/CXCR4 is “commandeered” by cancer cells to facilitate the spread of CXCR4-bearing tumor cells to tissues with high CXCL12 concentrations. High CXCR4 expression by cancer cells predisposes to aggressive spread and metastasis and ultimately to poor patient outcomes. As well as being useful as a marker for disease progression, CXCR4 is a potential target for anticancer therapies. It is possible to interfere directly with the CXCL12:CXCR4 axis using peptide or small-molecular-weight antagonists. A further opportunity is offered by promoting strategies that downregulate CXCR4 pathways: CXCR4 expression in the tumor microenvironment is modulated by factors such as hypoxia, nucleosides, and eicosanoids. Another promising approach is through targeting PPAR to suppress CXCR4 expression. Endogenous PPARγ such as 15-deoxy-Δ^12,14-PGJ₂ and synthetic agonists such as the thiazolidinediones both cause downregulation of CXCR4 mRNA and receptor. Adjuvant therapy using PPARγ agonists may, by stimulating PPARγ-dependent downregulation of CXCR4 on cancer cells, slow the rate of metastasis and impact beneficially on disease progression.

The dietary flavonoid apigenin enhances the activities of the anti-metastatic protein CD26 on human colon carcinoma cells

There is accumulating evidence that secondary plant metabolites such as flavonoids may have anti-cancer properties, and yet the molecular pathways that lead to alterations in cancer cell behaviour remain unclear. We investigated the possible actions of apigenin, a flavone present in leafy vegetables like parsley, on the levels of CD26 in carcinoma cells. CD26 is a multifunctional cell-surface protein that through its associated dipeptidyl peptidase (DPPIV) and ecto-adenosine deaminase (eADA) enzyme activities is able to suppress pathways involved in tumour metastasis. CD26 is down-regulated in various cancers including colorectal carcinoma. Apigenin substantially up-regulated cell-surface CD26 on HT-29 and HRT-18 human colorectal cancer cells. Levels of CD26 protein, along with its associated DPPIV enzyme activity, capacity to bind eADA, and ability to link cells to fibronectin, were increased with a maximum after 24-48 h. Elevation of CD26 occurred at concentrations that were at least 10-fold less than those shown to affect cell growth, and 100-fold below those that could affect cell viability. Furthermore, the CD26 effect was enhanced when apigenin was paired with chemotherapeutic agents utilized in the treatment of advanced colorectal cancer including irinotecan, 5-fluorouracil and oxaliplatin. For irinotecan, apigenin caused a 4-fold increase in the potency of the drug. These results demonstrate that apigenin can increase the cellular levels of CD26 and its multiple functions, and may oppose the predicted effect of decreased DPPIV and eADA activities on carcinoma cells, which is to facilitate tumour growth and metastasis.

Cancer biomarker discovery: the entropic hallmark

Background

It is a commonly accepted belief that cancer cells modify their transcriptional state during the progression of the disease. We propose that the progression of cancer cells towards malignant phenotypes can be efficiently tracked using high-throughput technologies that follow the gradual changes observed in the gene expression profiles by employing Shannon's mathematical theory of communication. Methods based on Information Theory can then quantify the divergence of cancer cells' transcriptional profiles from those of normally appearing cells of the originating tissues. The relevance of the proposed methods can be evaluated using microarray datasets available in the public domain but the method is in principle applicable to other high-throughput methods.

Methodology/Principal Findings

Using melanoma and prostate cancer datasets we illustrate how it is possible to employ Shannon Entropy and the Jensen-Shannon divergence to trace the transcriptional changes progression of the disease. We establish how the variations of these two measures correlate with established biomarkers of cancer progression. The Information Theory measures allow us to identify novel biomarkers for both progressive and relatively more sudden transcriptional changes leading to malignant phenotypes. At the same time, the methodology was able to validate a large number of genes and processes that seem to be implicated in the progression of melanoma and prostate cancer.

Conclusions/Significance

We thus present a quantitative guiding rule, a new unifying hallmark of cancer: the cancer cell's transcriptome changes lead to measurable observed transitions of Normalized Shannon Entropy values (as measured by high-througput technologies). At the same time, tumor cells increment their divergence from the normal tissue profile increasing their disorder via creation of states that we might not directly measure. This unifying hallmark allows, via the the Jensen-Shannon divergence, to identify the arrow of time of the processes from the gene expression profiles, and helps to map the phenotypical and molecular hallmarks of specific cancer subtypes. The deep mathematical basis of the approach allows us to suggest that this principle is, hopefully, of general applicability for other diseases.

Constitutive activation of BMP signalling abrogates experimental metastasis of OVCA429 cells via reduced cell adhesion

Background

Activation of bone morphogenetic protein (BMP)4 signalling in human ovarian cancer cells induces a number of phenotypic changes in vitro, including altered cell morphology, adhesion, motility and invasion, relative to normal human ovarian surface epithelial cells. From these in vitro analyses, we had hypothesized that active BMP signalling promotes the metastatic potential of ovarian cancer.

Methods

To test this directly, we engineered OVCA429 human ovarian cancer cells possessing doxycycline-inducible expression of a constitutively-active mutant BMP receptor, ALK3^QD, and administered these cells to immunocompromised mice. Further characterization was performed in vitro to address the role of activated BMP signalling on the EOC phenotype, with particular emphasis on epithelial-mesenchymal transition (EMT) and cell adhesion.

Results

Unexpectedly, doxycycline-induced ALK3^QD expression in OVCA429 cells reduced tumour implantation on peritoneal surfaces and ascites formation when xenografted into immunocompromised mice by intraperitoneal injection. To determine the potential mechanisms controlling this in vivo observation, we followed with several cell culture experiments. Doxycycline-induced ALK3^QD expression enhanced the refractile, spindle-shaped morphology of cultured OVCA429 cells eliciting an EMT-like response. Using in vitro wound healing assays, we observed that ALK3^QD-expressing cells migrated with long, cytoplasmic projections extending into the wound space. The phenotypic alterations of ALK3^QD-expressing cells correlated with changes in specific gene expression patterns of EMT, including increased Snail and Slug and reduced E-cadherin mRNA expression. In addition, ALK3^QD signalling reduced β1- and β3-integrin expression, critical molecules involved in ovarian cancer cell adhesion. The combination of reduced E-cadherin and β-integrin expression correlates directly with the reduced EOC cell cohesion in spheroids and reduced cell adhesion to the extracellular matrix substrates fibronectin and vitronectin that was observed.

Conclusions

We propose that the key steps of ovarian cancer metastasis, specifically cell cohesion of multicellular aggregates in ascites and cell adhesion for reattachment to secondary sites, may be inhibited by overactive BMP signalling, thereby decreasing the ultimate malignant potential of ovarian cancer in this model system.

Anti-CD73 antibody therapy inhibits breast tumor growth and metastasis

Extracellular adenosine is a potent immunosuppressor that accumulates during tumor growth. We performed proof-of-concept studies investigating the therapeutic potential and mechanism of action of monoclonal antibody (mAb)-based therapy against CD73, an ecto-enzyme overexpressed on breast-cancer cells that catalyzes the dephosphorylation of adenosine monophosphates into adenosine. We showed that anti-CD73 mAb therapy significantly delayed primary 4T1.2 and E0771 tumor growth in immune-competent mice and significantly inhibited the development of spontaneous 4T1.2 lung metastases. Notably, anti-CD73 mAb therapy was essentially dependent on the induction of adaptive anti-tumor immune responses. Knockdown of CD73 in 4T1.2 tumor cells confirmed the tumor-promoting effects of CD73. In addition to its immunosuppressive effect, CD73 enhanced tumor-cell chemotaxis, suggesting a role for CD73-derived adenosine in tumor metastasis. Accordingly, administration of adenosine-5'-N-ethylcarboxamide to tumor-bearing mice significantly enhanced spontaneous 4T1.2 lung metastasis. Using selective adenosine-receptor antagonists, we showed that activation of A2B adenosine receptors promoted 4T1.2 tumor-cell chemotaxis in vitro and metastasis in vivo. In conclusion, our study identified tumor-derived CD73 as a mechanism of tumor immune escape and tumor metastasis, and it also established the proof of concept that targeted therapy against CD73 can trigger adaptive anti-tumor immunity and inhibit metastasis of breast cancer.

15-Deoxy-delta(12,14)-prostaglandin J(2) down-regulates CXCR4 on carcinoma cells through PPARgamma- and NFkappaB-mediated pathways

The chemokine receptor CXCR4 plays a key role in the metastasis of colorectal cancer and its growth at metastatic sites. Here, we have investigated the mechanisms by which CXCR4 on cancer cells might be regulated by eicosanoids present within the colorectal tumor microenvironment. We show that prostaglandins PGE(2), PGA(2), PGD(2), PGJ(2) and 15dPGJ(2) each down-regulates CXCR4 receptor expression on human colorectal carcinoma cells to differing degrees. The most potent of these were PGD(2) and its metabolites PGJ(2) and 15dPGJ(2). Down-regulation was most rapid with the end-product 15dPGJ(2) and was accompanied by a marked reduction in CXCR4 mRNA. 15dPGJ(2) is known to be a ligand for the nuclear receptor PPARgamma. Down-regulation of CXCR4 was also observed with the PPARgamma agonist rosiglitazone, while 15dPGJ(2)-induced CXCR4 down-regulation was substantially diminished by the PPARgamma antagonists GW9662 and T0070907. These data support the involvement of PPARgamma. However, the 15dPGJ(2) analogue CAY10410, which can act on PPARgamma but which lacks the intrinsic cyclopentenone structure found in 15dPGJ(2), down-regulated CXCR4 substantially less potently than 15dPGJ(2). The cyclopentenone grouping is known to inhibit the activity of NFkappaB. Consistent with an additional role for NFkappaB, we found that the cyclopentenone prostaglandin PGA(2) and cyclopentenone itself could also down-regulate CXCR4. Immunolocalization studies showed that the cellular context was sufficient to trigger a focal nuclear pattern of NFkappaB p50 and that 15dPGJ(2) interfered with this p50 nuclear localization. These data suggest that 15dPGJ(2) can down-regulate CXCR4 on cancer cells through both PPARgamma and NFkappaB. 15dPGJ(2), present within the tumor microenvironment, may act to down-regulate CXCR4 and impact upon the overall process of tumor expansion.

Adenosine receptors in colon carcinoma tissues and colon tumoral cell lines: focus on the A(3) adenosine subtype

Adenosine may affect several pathophysiological processes, including cellular proliferation, through interaction with A(1), A(2A), A(2B), and A(3) receptors. In this study we characterized adenosine receptors in human colon cancer tissues and in colon cancer cell lines Caco2, DLD1, HT29. mRNA of all adenosine subtypes was detected in cancer tissues and cell lines. At a protein levels low amount of A(1), A(2A), and A(2B) receptors were detected, whilst the A(3) was the most abundant subtype in both cancer tissues and cells, with a pharmacological profile typical of the A(3) subtype. All the receptors were coupled to stimulation/inhibition of adenylyl-cyclase in cancer cells, with the exception of A(1) subtype. Adenosine increased cell proliferation with an EC(50) of 3-12 microM in cancer cells. This effect was not essentially reduced by adenosine receptor antagonists. However dypiridamol, an adenosine transport inhibitor, increased the stimulatory effect induced by adenosine, suggesting an action at the cell surface. Addition of adenosine deaminase makes the A(3) agonist 2-chloro-N6-(3-iodobenzyl)-N-methyl-5'-carbamoyladenosine (Cl-IB-MECA) able to stimulate cell proliferation with an EC(50) of 0.5-0.9 nM in cancer cells, suggesting a tonic proliferative effect induced by endogenous adenosine. This effect was antagonized by 5-N-(4-methoxyphenyl-carbamoyl)amino-8-propyl-2(2furyl)-pyrazolo-[4,3e]-1,2,4-triazolo [1,5-c] pyrimidine (MRE 3008F20) 10 nM. Cl-IB-MECA-stimulated cell proliferation involved extracellular-signal-regulated-kinases (ERK1/2) pathway, as demonstrated by reduction of proliferation with 1,4-diamino-2,3-dicyano-1,4-bis-[2-amino-phenylthio]-butadiene (U0126) and by ERK1/2 phosphorylation. In conclusion this study indicates for the first time that in colon cancer cell lines endogenous adenosine, through the interaction with A(3) receptors, mediates a tonic proliferative effect.

BMP4 induces EMT and Rho GTPase activation in human ovarian cancer cells

We identified previously an autocrine bone morphogenetic protein-4 (BMP4) signalling pathway in primary human normal ovarian surface epithelial (OSE) and epithelial ovarian cancer (OvCa) cells. Herein we show that treatment of OvCa cells with BMP4 produced morphological alterations and increased cellular adhesion, motility and invasion. The BMP4 inhibitor noggin blocked the BMP4-induced phenotype, and decreased autocrine BMP4-mediated OvCa cell motility and adherence. In response to exogenous BMP4, the epithelial-mesenchymal transition (EMT) markers Snail and Slug mRNA and protein were up-regulated, E-cadherin mRNA and protein were down-regulated and the network of alpha smooth muscle actin changed to resemble a mesenchymal cell. We also observed changes in the level of activated Rho GTPases in OvCa cells treated with BMP4, strongly suggesting that the changes in morphology, adhesion, motility and invasion are probably mediated through the activation of these molecules. Strikingly, treatment of normal OSE cells with BMP4 or noggin failed to alter cell motility, providing evidence that OSE and OvCa cells possess a distinct capability to respond to BMP4. Overall, our studies suggest a link between autocrine BMP signalling mediated through the Rho GTPase family and Snail- and Slug-induced EMT that may collectively contribute to aggressive OvCa behaviour.

DPPIV inhibitors extend GLP-2 mediated tumour promoting effects on intestinal cancer cells

BACKGROUND

The glucagon-like peptides-1 and -2 (GLP-1 and -2) are co-secreted after food intake from intestinal L cells. Since both peptides are rapidly degraded by dipeptidyl peptidase-IV (DPPIV), research is focused on the development of DPPIV inhibitors or DPPIV resistant.

AIMS

In this study we investigated, whether the inhibition of DPPIV activity and the resulting increased half-life of DPPIV substrates may influence cancer development and progression.

METHODS

We examined proliferation and migratory activity of two human colon cancer cell lines (SW480, HT29) after stimulation with GLP-2 in combination with or without DPPIV inhibitors.

RESULTS

Migratory activity was increased by 25% from 20% matrix induced activity to a maximum of 45% (100 nM GLP-2). In cells expressing CD26, migration was prolonged by addition of DPPIV inhibitors in a concentration dependent manner. After treatment with GLP-2 doubling time decreased from 2.4 to 1.5 days - and addition of DPPIV inhibitors enhanced the effect of GLP-2.

CONCLUSIONS

The use of DPPIV inhibitors together with GLP-2 led to increased proliferation as well as elevated migratory activity. Therefore, the use of DPPIV inhibitors could increase the risk of promoting an already existing intestinal tumour and may support the potential of colon cancer cells to metastasize.

Adenosine upregulates CXCR4 and enhances the proliferative and migratory responses of human carcinoma cells to CXCL12/SDF-1alpha

The level of expression of the chemokine receptor CXCR4 has been shown to play a crucial role in determining the ability of cancer cells to metastasize from the primary tumor and become established in tissue sites that are rich in the CXCR4 ligand CXCL12/SDF-1alpha. High CXCR4 expression on cancer cells is associated with an increased risk of recurrence and poorer overall survival. We propose that local tissue mediators within the primary tumor or at secondary sites may modulate the level of CXCR4 expression and, therefore, potentially affect the ability of the cancer cells to metastasize. The purine nucleoside adenine-9-beta-D-ribofuranoside (adenosine) is generated at high concentrations within the extracellular fluid of solid tumors because of their hypoxia. We show here that adenosine acts through A(2A) and A(2B) adenosine receptors on human colorectal carcinoma cells to upregulate CXCR4 mRNA expression up to 10-fold and selectively increases cell-surface CXCR4 protein up to 3-fold. This increase in cell-surface CXCR4 enables the carcinoma cells to migrate toward CXCL12, and enhances their proliferation in response to CXCL12. Adenosine may therefore be one of the factors within the tumor microenvironment that facilitates tumor dissemination, by upregulating CXCR4 on certain cancer cells and enhancing cellular responses to CXCL12.

Adenosine downregulates DPPIV on HT-29 colon cancer cells by stimulating protein tyrosine phosphatase(s) and reducing ERK1/2 activity via a novel pathway

The multifunctional cell-surface protein dipeptidyl peptidase IV (DPPIV/CD26) is aberrantly expressed in many cancers and plays a key role in tumorigenesis and metastasis. Its diverse cellular roles include modulation of chemokine activity by cleaving dipeptides from the chemokine NH(2)-terminus, perturbation of extracellular nucleoside metabolism by binding the ecto-enzyme adenosine deaminase, and interaction with the extracellular matrix by binding proteins such as collagen and fibronectin. We have recently shown that DPPIV can be downregulated from the cell surface of HT-29 colorectal carcinoma cells by adenosine, which is a metabolite that becomes concentrated in the extracellular fluid of hypoxic solid tumors. Most of the known responses to adenosine are mediated through four different subtypes of G protein-coupled adenosine receptors: A(1), A(2A), A(2B), and A(3). We report here that adenosine downregulation of DPPIV from the surface of HT-29 cells occurs independently of these classic receptor subtypes, and is mediated by a novel cell-surface mechanism that induces an increase in protein tyrosine phosphatase activity. The increase in protein tyrosine phosphatase activity leads to a decrease in the tyrosine phosphorylation of ERK1/2 MAP kinase that in turn links to the decline in DPPIV mRNA and protein. The downregulation of DPPIV occurs independently of changes in the activities of protein kinases A or C, phosphatidylinositol 3-kinase, other serine/threonine phosphatases, or the p38 or JNK MAP kinases. This novel action of adenosine has implications for our ability to manipulate adenosine-dependent events within the solid tumor microenvironment.