Platelet-Mimicry of Cancer Cells: Epiphenomenon with Clinical Significance

In vitro cross-talk between metastasis-competent circulating tumor cells and platelets in colon cancer: a malicious association during the harsh journey in the blood

Background: Platelets are active players in hemostasis, coagulation and also tumorigenesis. The cross-talk between platelets and circulating tumor cells (CTCs) may have various pro-cancer effects, including promoting tumor growth, epithelial-mesenchymal transition (EMT), metastatic cell survival, adhesion, arrest and also pre-metastatic niche and metastasis formation. Interaction with CTCs might alter the platelet transcriptome. However, as CTCs are rare events, the cross-talk between CTCs and platelets is poorly understood. Here, we used our established colon CTC lines to investigate the colon CTC-platelet cross-talk in vitro and its impact on the behavior/phenotype of both cell types. Methods: We exposed platelets isolated from healthy donors to thrombin (positive control) or to conditioned medium from three CTC lines from one patient with colon cancer and then we monitored the morphological and protein expression changes by microscopy and flow cytometry. We then analyzed the transcriptome by RNA-sequencing of platelets indirectly (presence of a Transwell insert) co-cultured with the three CTC lines. We also quantified by reverse transcription-quantitative PCR the expression of genes related to EMT and cancer development in CTCs after direct co-culture (no Transwell insert) with platelets. Results: We observed morphological and transcriptomic changes in platelets upon exposure to CTC conditioned medium and indirect co-culture (secretome). Moreover, the expression levels of genes involved in EMT (p < 0.05) were decreased in CTCs co-cultured with platelets, but not of genes encoding mesenchymal markers (FN1 and SNAI2). The expression levels of genes involved in cancer invasiveness (MYC, VEGFB, IL33, PTGS2, and PTGER2) were increased. Conclusion: For the first time, we studied the CTC-platelet cross-talk using our unique colon CTC lines. Incubation with CTC conditioned medium led to platelet aggregation and activation, supporting the hypothesis that their interaction may contribute to preserve CTC integrity during their journey in the bloodstream. Moreover, co-culture with platelets influenced the expression of several genes involved in invasiveness and EMT maintenance in CTCs.

Newly identified form of phenotypic plasticity of cancer: immunogenic mimicry

Cancer plasticity is now a recognized new hallmark of cancer which is due to disturbances of cell differentiation programs. It is manifested not only in various forms like the best-known epithelial-mesenchymal transition (EMT) but also in vasculogenic and megakaryocytic mimicries regulated by EMT-specific or less-specific transcription factors such as HIF1a or STAT1/2. Studies in the past decades provided ample data that cancer plasticity can be manifested also in the expression of a vast array of immune cell genes; best-known examples are PDL1/CD274, CD47, or IDO, and we termed it immunogenic mimicry (IGM). However, unlike other types of plasticities which are epigenetically regulated, expression of IGM genes are frequently due to gene amplifications. It is important that the majority of the IGM genes are regulated by interferons (IFNs) suggesting that their protein expressions are regulated by the immune microenvironment. Most of the IGM genes have been shown to be involved in immune escape of cancers broadening the repertoire of these mechanisms and offering novel targets for immunotherapeutics.

Effects of the interactions between platelets with other cells in tumor growth and progression

It has been confirmed that platelets play a key role in tumorigenesis. Tumor-activated platelets can recruit blood cells and immune cells to migrate, establish an inflammatory tumor microenvironment at the sites of primary and metastatic tumors. On the other hand, they can also promote the differentiation of mesenchymal cells, which can accelerate the proliferation, genesis and migration of blood vessels. The role of platelets in tumors has been well studied. However, a growing number of studies suggest that interactions between platelets and immune cells (e.g., dendritic cells, natural killer cells, monocytes, and red blood cells) also play an important role in tumorigenesis and tumor development. In this review, we summarize the major cells that are closely associated with platelets and discuss the essential role of the interaction between platelets with these cells in tumorigenesis and tumor development.

Platelet-Cancer Interplay: Molecular Mechanisms and New Therapeutic Avenues

Although platelets are critically involved in thrombosis and hemostasis, experimental and clinical evidence indicate that platelets promote tumor progression and metastasis through a wide range of physical and functional interactions between platelets and cancer cells. Thrombotic and thromboembolic events are frequent complications in patients with solid tumors. Hence, cancer modulates platelet function by directly inducing platelet-tumor aggregates and triggering platelet granule release and altering platelet turnover. Also, platelets enhance tumor cell dissemination by activating endothelial cell function and recruiting immune cells to primary and metastatic tumor sites. In this review, we summarize current knowledge on the complex interactions between platelets and tumor cells and the host microenvironment. We also critically discuss the potential of anti-platelet agents for cancer prevention and treatment.

Hypoxia Signaling in Cancer: From Basics to Clinical Practice

Cancer hypoxia, recognized as one of the most important hallmarks of cancer, affects gene expression, metabolism and ultimately tumor biology-related processes. Major causes of cancer hypoxia are deficient or inappropriate vascularization and systemic hypoxia of the patient (frequently induced by anemia), leading to a unique form of genetic reprogramming by hypoxia induced transcription factors (HIF). However, constitutive activation of oncogene-driven signaling pathways may also activate hypoxia signaling independently of oxygen supply. The consequences of HIF activation in tumors are the angiogenic phenotype, a novel metabolic profile and the immunosuppressive microenvironment. Cancer hypoxia and the induced adaptation mechanisms are two of the major causes of therapy resistance. Accordingly, it seems inevitable to combine various therapeutic modalities of cancer patients by existing anti-hypoxic agents such as anti-angiogenics, anti-anemia therapies or specific signaling pathway inhibitors. It is evident that there is an unmet need in cancer patients to develop targeted therapies of hypoxia to improve efficacies of various anti-cancer therapeutic modalities. The case has been opened recently due to the approval of the first-in-class HIF2α inhibitor.

Platelets and tumor-associated RNA transfer

Until recently, the nucleic acid content of platelets was considered to be fully determined by their progenitor megakaryocyte. However, it is now well understood that additional mediators (eg, cancer cells) can intervene, thereby influencing the RNA repertoire of platelets. Platelets are highly dynamic cells that are able to communicate and influence their environment. For instance, platelets have been involved in various steps of cancer development and progression by supporting tumor growth, survival, and dissemination. Cancer cells can directly and/or indirectly influence platelet RNA content, resulting in tumor-mediated "education" of platelets. Alterations in the tumor-educated platelet RNA profile have been described as a novel source of potential biomarkers. Individual platelet RNA biomarkers as well as complex RNA signatures may be used for early detection of cancer and treatment monitoring. Here, we review the RNA transfer occurring between cancer cells and platelets. We explore the potential use of platelet RNA biomarkers as a liquid biopsy biosource and discuss methods to evaluate the transcriptomic content of platelets.

Autophagy Process in Trophoblast Cells Invasion and Differentiation: Similitude and Differences With Cancer Cells

Early human placental development begins with blastocyst implantation, then the trophoblast differentiates and originates the cells required for a proper fetal nutrition and placental implantation. Among them, extravillous trophoblast corresponds to a non-proliferating trophoblast highly invasive that allows the vascular remodeling which is essential for appropriate placental perfusion and to maintain the adequate fetal growth. This process involves different placental cell types as well as molecules that allow cell growth, cellular adhesion, tissular remodeling, and immune tolerance. Remarkably, some of the cellular processes required for proper placentation are common between placental and cancer cells to finally support tumor growth. Indeed, as in placentation trophoblasts invade and migrate, cancer cells invade and migrate to promote tumor metastasis. However, while these processes respond to a controlled program in trophoblasts, in cancer cells this regulation is lost. Interestingly, it has been shown that autophagy, a process responsible for the degradation of damaged proteins and organelles to maintain cellular homeostasis, is required for invasion of trophoblast cells and for vascular remodeling during placentation. In cancer cells, autophagy has a dual role, as it has been shown both as tumor promoter and inhibitor, depending on the stage and tumor considered. In this review, we summarized the similarities and differences between trophoblast cell invasion and cancer cell metastasis specifically evaluating the role of autophagy in both processes.

Multifaceted Functions of Platelets in Cancer: From Tumorigenesis to Liquid Biopsy Tool and Drug Delivery System

Platelets contribute to several types of cancer through plenty of mechanisms. Upon activation, platelets release many molecules, including growth and angiogenic factors, lipids, and extracellular vesicles, and activate numerous cell types, including vascular and immune cells, fibroblasts, and cancer cells. Hence, platelets are a crucial component of cell-cell communication. In particular, their interaction with cancer cells can enhance their malignancy and facilitate the invasion and colonization of distant organs. These findings suggest the use of antiplatelet agents to restrain cancer development and progression. Another peculiarity of platelets is their capability to uptake proteins and transcripts from the circulation. Thus, cancer-patient platelets show specific proteomic and transcriptomic expression patterns, a phenomenon called tumor-educated platelets (TEP). The transcriptomic/proteomic profile of platelets can provide information for the early detection of cancer and disease monitoring. Platelet ability to interact with tumor cells and transfer their molecular cargo has been exploited to design platelet-mediated drug delivery systems to enhance the efficacy and reduce toxicity often associated with traditional chemotherapy. Platelets are extraordinary cells with many functions whose exploitation will improve cancer diagnosis and treatment.

Platelets in aging and cancer-"double-edged sword"

Platelets control hemostasis and play a key role in inflammation and immunity. However, platelet function may change during aging, and a role for these versatile cells in many age-related pathological processes is emerging. In addition to a well-known role in cardiovascular disease, platelet activity is now thought to contribute to cancer cell metastasis and tumor-associated venous thromboembolism (VTE) development. Worldwide, the great majority of all patients with cardiovascular disease and some with cancer receive anti-platelet therapy to reduce the risk of thrombosis. However, not only do thrombotic diseases remain a leading cause of morbidity and mortality, cancer, especially metastasis, is still the second cause of death worldwide. Understanding how platelets change during aging and how they may contribute to aging-related diseases such as cancer may contribute to steps taken along the road towards a "healthy aging" strategy. Here, we review the changes that occur in platelets during aging, and investigate how these versatile blood components contribute to cancer progression.

SASP-Dependent Interactions between Senescent Cells and Platelets Modulate Migration and Invasion of Cancer Cells

Alterations in platelet aggregation are common in aging individuals and in the context of age-related pathologies such as cancer. So far, however, the effects of senescent cells on platelets have not been explored. In addition to serving as a barrier to tumor progression, cellular senescence can contribute to remodeling tissue microenvironments through the capacity of senescent cells to synthesize and secrete a plethora of bioactive factors, a feature referred to as the senescence-associated secretory phenotype (SASP). As senescent cells accumulate in aging tissues, sites of tissue injury, or in response to drugs, SASP factors may contribute to increase platelet activity and, through this mechanism, generate a microenvironment that facilitates cancer progression. Using in vitro models of drug-induced senescence, in which cellular senescence was induced following exposure of mammary epithelial cells (MCF-10A and MCF-7) and gastric cancer cells (AGS) to the CDK4/6 inhibitor Palbociclib, we show that senescent mammary and gastric cells display unique expression profiles of selected SASP factors, most of them being downregulated at the RNA level in senescent AGS cells. In addition, we observed cell-type specific differences in the levels of secreted factors, including IL-1β, in media conditioned by senescent cells. Interestingly, only media conditioned by senescent MCF-10A and MCF-7 cells were able to enhance platelet aggregation, although all three types of senescent cells were able to attract platelets in vitro. Nevertheless, the effects of factors secreted by senescent cells and platelets on the migration and invasion of non-senescent cells are complex. Overall, platelets have prominent effects on migration, while factors secreted by senescent cells tend to promote invasion. These differential responses likely reflect differences in the specific arrays of secreted senescence-associated factors, specific factors released by platelets upon activation, and the susceptibility of target cells to respond to these agents.

Prognostic index score predicts outcome of patients with Stage I non-small cell lung cancer after stereotactic body radiation therapy

OBJECTIVE

Lung cancer is the most common causes of cancer death worldwide and patients with non-small-cell lung cancer (NSCLC) have various prognosis. We conducted this study to identify the prognostic predictors and establish a prognostic index score (PIS) for patients with Stage I NSCLC after stereotactic body radiation therapy (SBRT).

METHODS

A total of 131 consecutive patients with Stage I NSCLC who underwent SBRT in our institute were analyzed retrospectively. The Cox proportional hazards regression model was applied to identify the prognostic predictors. Time-dependent receiver operating characteristic analysis was performed to examine cutoff values for survival. The Kaplan-Meier method with log-rank test was used to compare survival curves.

RESULTS

Univariate analysis indicated that tumor location, maximum standardized uptake value (SUVmax), monocyte counts and platelet-to-lymphocyte ratio (PLR) were prognostic factors of overall survival (OS). SUVmax and PLR remained significant in multivariate analysis. Survival analysis indicated both high-SUVmax and PLR correlated with inferior OS and PFS. A PIS was constructed based on pretreatment SUVmax and PLR and a high PIS was also significantly associated with poor outcome.

CONCLUSION

The pretreatment SUVmax and PLR were independent prognostic factors of OS in patients with Stage I NSCLC after SBRT. PIS provides a convenient and accurate tool for predicting outcome of patients after SBRT.

Platelets and extracellular vesicles in cancer: diagnostic and therapeutic implications

Several pieces of evidence support the role of activated platelets in the development of the chronic inflammation-related diseases, such as atherothrombosis and cancer, mainly via the release of soluble factors and microparticles (MPs). Platelets and MPs contain a repertoire of proteins and genetic material (i.e., mRNAs and microRNAs) which may be influenced by the clinical condition of the individuals. In fact, platelets are capable of up-taking proteins and genetic material during their lifespan. Moreover, the content of platelet-derived MPs can be delivered to other cells, including stromal, immune, epithelial, and cancer cells, to change their phenotype and functions, thus contributing to cancer promotion and its metastasization. Platelets and MPs can play an indirect role in the metastatic process by helping malignant cells to escape from immunological surveillance. Furthermore, platelets and their derived MPs represent a potential source for blood biomarker development in oncology. This review provides an updated overview of the roles played by platelets and MPs in cancer and metastasis formation. The possible analysis of platelet and MP molecular signatures for the detection of cancer and monitoring of anticancer treatments is discussed. Finally, the potential use of MPs as vectors for drug delivery systems to cancer cells is put forward.

The role of lipid signaling in the progression of malignant melanoma

In the past decades, a vast amount of data accumulated on the role of lipid signaling pathways in the progression of malignant melanoma, the most metastatic/aggressive human cancer type. Genomic studies identified that PTEN loss is the leading factor behind the activation of the PI3K-signaling pathway in melanoma, mutations of which are one of the main resistance mechanisms behind target therapy failures. On the other hand, illegitimate expressions of megakaryocytic genes p12-lipoxyganse, cyclooxygenase-2, and phosphodiestherase-2/autotaxin (ATX) are mostly involved in the regulation of motility signaling in melanoma through various G-protein-coupled bioactive lipid receptors. Furthermore, endocannabinoid signaling can also be a novel paracrine survival factor in melanoma. Last but not least, prenylation inhibitors acting even on mutated small GTP-ases, such as NRAS of melanoma may offer novel therapeutic opportunities. As regards melanoma, the most effective therapy nowadays is immunotherapy, with the resistance mechanisms also possibly involving the lipid signaling activities of melanoma cells, which further supports the idea of their being therapeutic targets.

Multifaceted role of cancer educated platelets in survival of cancer cells

Platelets, the derivatives of megakaryocytes, pose dynamic biological functions such as homeostasis and wound healing. The mechanisms involved in these processes are utilized by cancerous cells for proliferation and metastasis. Platelets through their activation establish an aggregate termed as Tumor cell induced platelet aggregation (TCIPA) that aids in establishing a niche for the primary tumor at secondary site while recruiting granulocytes and monocytes. The study of these close interactions between the tumor and the platelets can be exploited as biomarkers in liquid biopsy for early cancer detection, thereby increasing the life expectancy of cancer patients.

Platelets in cancer development and diagnosis

Platelets are involved in the development and progression of cancer through several mechanisms. Platelet activation at the site of tissue damage contributes to the initiation of a cascade of events which promote tumorigenesis. In fact, platelets release a wide array of proteins, including growth and angiogenic factors, lipids and extracellular vesicles rich in genetic material, which can mediate the induction of phenotypic changes in target cells, such as immune, stromal and tumor cells, and promote carcinogenesis and metastasis formation. Importantly, the role of platelets in tumor immune escape has been described. These lines of evidence open the way to novel strategies to fight cancer based on the use of antiplatelet agents. In addition to their ability to release factors, platelets are able of up-taking proteins and genetic material present in the bloodstream. Platelets are like 'sentinels' of the disease state. The evaluation of proteomics and transcriptomics signature of platelets and platelet-derived microparticles could represent a new strategy for the development of biomarkers for early cancer detection and/or therapeutic drug monitoring in cancer chemotherapy. Owing to the ability of platelets to interact with cancer cells and to deliver their cargo, platelets have been proposed as a 'biomimetic drug delivery system' for anti-tumor drugs to prevent the occurrence of off-target adverse events associated with the use of traditional chemotherapy.

Antithrombotic Agents and Cancer

Platelet activation is the first response to tissue damage and, if unrestrained, may promote chronic inflammation-related cancer, mainly through the release of soluble factors and vesicles that are rich in genetic materials and proteins. Platelets also sustain cancer cell invasion and metastasis formation by fostering the development of the epithelial-mesenchymal transition phenotype, cancer cell survival in the bloodstream and arrest/extravasation at the endothelium. Furthermore, platelets contribute to tumor escape from immune elimination. These findings provide the rationale for the use of antithrombotic agents in the prevention of cancer development and the reduction of metastatic spread and mortality. Among them, low-dose aspirin has been extensively evaluated in both preclinical and clinical studies. The lines of evidence have been considered appropriate to recommend the use of low-dose aspirin for primary prevention of cardiovascular disease and colorectal cancer by the USA. Preventive Services Task Force. However, two questions are still open: (i) the efficacy of aspirin as an anticancer agent shared by other antiplatelet agents, such as clopidogrel; (ii) the beneficial effect of aspirin improved at higher doses or by the co-administration of clopidogrel. This review discusses the latest updates regarding the mechanisms by which platelets promote cancer and the efficacy of antiplatelet agents.

An insight into metastasis: Random or evolving paradigms?

Mechanical or fostered molecular events define metastatic cascade. Three distinct sets of molecular events characterize metastasis, viz invasion of extracellular matrix; angiogenesis, vascular dissemination and anoikis resistance; tumor homing and relocation of tumor cells to selective organ. Invasion of extracellular matrix requires epithelial to mesenchymal transition through disrupted lamellopodia formation and contraction of actin cytoskeleton; aberration of Focal adhesion complex formation involving integrins and the extracellular matrix; degradation of extracellular matrix by matrix metalloproteases; faulty immune surveillance in tumor microenvironment and an upregulated proton efflux pump NHE1 in tumors. Vascular dissemination and anoikis resistance depend upon upregulation of integrins, phosphorylation of CDCP1, attenuated apoptotic pathways and upregulation of angiogenesis. Tumor homing depends on recruitment of mesenchymal stem cells, expression on chemokines and growth factors, upregulated stem cell renewal pathways. Despite of many potential challenges in curbing metastasis, future targeted therapies involving immunotherapy, stem cell engineered and oncolytic virus based therapy, pharmacological activation of circadian clock are held promising. To sum up, metastasis is a complex cascade of events and warrants detailed molecular understanding for development of therapeutic strategies.

Cancer and platelet crosstalk: opportunities and challenges for aspirin and other antiplatelet agents

Platelets have long been recognized as key players in hemostasis and thrombosis; however, growing evidence suggests that they are also significantly involved in cancer, the second leading cause of mortality worldwide. Preclinical and clinical studies showed that tumorigenesis and metastasis can be promoted by platelets through a wide variety of crosstalk between platelets and cancer cells. For example, cancer changes platelet behavior by directly inducing tumor-platelet aggregates, triggering platelet granule and extracellular vesicle release, altering platelet phenotype and platelet RNA profiles, and enhancing thrombopoiesis. Reciprocally, platelets reinforce tumor growth with proliferation signals, antiapoptotic effect, and angiogenic factors. Platelets also activate tumor invasion and sustain metastasis via inducing an invasive epithelial-mesenchymal transition phenotype of tumor cells, promoting tumor survival in circulation, tumor arrest at the endothelium, and extravasation. Furthermore, platelets assist tumors in evading immune destruction. Hence, cancer cells and platelets maintain a complex, bidirectional communication. Recently, aspirin (acetylsalicylic acid) has been recognized as a promising cancer-preventive agent. It is recommended at daily low dose by the US Preventive Services Task Force for primary prevention of colorectal cancer. The exact mechanisms of action of aspirin in chemoprevention are not very clear, but evidence has emerged that suggests a platelet-mediated effect. In this article, we will introduce how cancer changes platelets to be more cancer-friendly and highlight advances in the modes of action for aspirin in cancer prevention. We also discuss the opportunities, challenges, and opposing viewpoints on applying aspirin and other antiplatelet agents for cancer prevention and treatment.

Collateral Damage Intended-Cancer-Associated Fibroblasts and Vasculature Are Potential Targets in Cancer Therapy

After oncogenic transformation, tumor cells rewire their metabolism to obtain sufficient energy and biochemical building blocks for cell proliferation, even under hypoxic conditions. Glucose and glutamine become their major limiting nutritional demands. Instead of being autonomous, tumor cells change their immediate environment not only by their metabolites but also by mediators, such as juxtacrine cell contacts, chemokines and other cytokines. Thus, the tumor cells shape their microenvironment as well as induce resident cells, such as fibroblasts and endothelial cells (ECs), to support them. Fibroblasts differentiate into cancer-associated fibroblasts (CAFs), which produce a qualitatively and quantitatively different extracellular matrix (ECM). By their contractile power, they exert tensile forces onto this ECM, leading to increased intratumoral pressure. Moreover, along with enhanced cross-linkage of the ECM components, CAFs thus stiffen the ECM. Attracted by tumor cell- and CAF-secreted vascular endothelial growth factor (VEGF), ECs sprout from pre-existing blood vessels during tumor-induced angiogenesis. Tumor vessels are distinct from EC-lined vessels, because tumor cells integrate into the endothelium or even mimic and replace it in vasculogenic mimicry (VM) vessels. Not only the VM vessels but also the characteristically malformed EC-lined tumor vessels are typical for tumor tissue and may represent promising targets in cancer therapy.

Platelets as crucial partners for tumor metastasis: from mechanistic aspects to pharmacological targeting

Platelets are anucleated cells that circulate in the blood as sentinels of tissue integrity. In fact, they are rich in a plethora of proteins and other factors stored in different granules which they selectively release upon stimulation. Moreover, platelets synthesize a vast number of lipids and release various types of vesicles, including exosomes which are rich in genetic material. Platelets possess a central function to interact with other cell types, including inflammatory cells and cancer cells. Recent findings have enlightened the capacity of platelets to induce changes in the phenotype of cancer cells which acquire invasiveness thus enhancing their metastatic potential. Thus, it has been hypothesized that targeting the platelet may represent a novel strategy to prevent the development and progression of cancer. This is supported by the efficacy of the antiplatelet agent low-dose aspirin. Studies are ongoing to verify whether other antiplatelet agents share the anticancer effectiveness of aspirin.

Patterns and functional implications of platelets upon tumor "education"

While platelets are traditionally recognized to play a predominant role in hemostasis and thrombosis, increasing evidence verifies its involvement in malignancies. As a component of the tumor microenvironment, platelets influence carcinogenesis, tumor metastasis and chemotherapy efficiency. Platelets status is thus predictable as a hematological biomarker of cancer prognosis and a hot target for therapeutic intervention. On the other hand, the role of circulating tumor cells (CTCs) as an inducer of platelet activation and aggregation has been well acknowledged. The cross-talk between platelets and CTCs is reciprocal on that the CTCs activate platelets while platelets contribute to CTCs' survival and dissemination. This review covers some of the current issues related to the loop between platelets and tumor aggression, including the manners of tumor cells in "educating" platelets and biofunctional alterations of platelets upon tumor "education". We also highlight the potential clinical applications on the interplay between tumors and platelets. Further studies with well-designed prospective multicenter trials may contribute to clinical "liquid biopsy" diagnosis by evaluating the global changes of platelets.

The Interaction of Selectins and PSGL-1 as a Key Component in Thrombus Formation and Cancer Progression

Cellular interaction is inevitable in the pathomechanism of human disease. Formation of heterotypic cellular aggregates, between distinct cells of hematopoietic and nonhematopoietic origin, may be involved in events leading to inflammation and the complex process of cancer progression. Among adhesion receptors, the family of selectins with their ligands have been considered as one of the major contributors to cell-cell interactions. Consequently, the inhibition of the interplay between selectins and their ligands may have potential therapeutic benefits. In this review, we focus on the current evidence on the selectins as crucial modulators of inflammatory, thrombotic, and malignant disorders. Knowing that there is promiscuity in selectin binding, we outline the importance of a key protein that serves as a ligand for all selectins. This dimeric mucin, the P-selectin glycoprotein ligand 1 (PSGL-1), has emerged as a major player in inflammation, thrombus, and cancer development. We discuss the interaction of PSGL-1 with various selectins in physiological and pathological processes with particular emphasis on mechanisms that lead to severe disease.

Genetic progression of malignant melanoma

Malignant melanoma of the skin is the most aggressive human cancer given that a primary tumor a few millimeters in diameter frequently has full metastatic competence. In view of that, revealing the genetic background of this potential may also help to better understand tumor dissemination in general. Genomic analyses have established the molecular classification of melanoma based on the most frequent driver oncogenic mutations (BRAF, NRAS, KIT) and have also revealed a long list of rare events, including mutations and amplifications as well as genetic microheterogeneity. At the moment, it is unclear whether any of these rare events have role in the metastasis initiation process since the major drivers do not have such a role. During lymphatic and hematogenous dissemination, the clonal selection process is evidently reflected by differences in oncogenic drivers in the metastases versus the primary tumor. Clonal selection is also evident during lymphatic progression, though the genetic background of this immunoselection is less clear. Genomic analyses of metastases identified further genetic alterations, some of which may correspond to metastasis maintenance genes. The natural genetic progression of melanoma can be modified by targeted (BRAF or MEK inhibitor) or immunotherapies. Some of the rare events in primary tumors may result in primary resistance, while further new genetic lesions develop during the acquired resistance to both targeted and immunotherapies. Only a few genetic lesions of the primary tumor are constant during natural or therapy-modulated progression. EGFR4 and NMDAR2 mutations, MITF and MET amplifications and PTEN loss can be considered as metastasis drivers. Furthermore, BRAF and MITF amplifications as well as PTEN loss are also responsible for resistance to targeted therapies, whereas NRAS mutation is the only founder genetic lesion showing any association with sensitivity to immunotherapies. Unfortunately, there are hardly any data on the possible organ-specific metastatic drivers in melanoma. These observations suggest that clinical management of melanoma patients must rely on the genetic analysis of the metastatic lesions to be able to monitor progression-associated changes and to personalize therapies.

Tumor-Associated Macrophages and Neutrophils in Tumor Microenvironment

Distinct tumor microenvironment forms in each progression step of cancer and has diverse capacities to induce both adverse and beneficial consequences for tumorigenesis. It is now known that immune cells can be activated to favor tumor growth and progression, most probably influenced by the tumor microenvironment. Tumor-associated macrophages and tumor-associated neutrophils can exert protumoral functions, enhancing tumor cell invasion and metastasis, angiogenesis, and extracellular matrix remodeling, while inhibiting the antitumoral immune surveillance. Considering that neutrophils in inflammatory environments recruit macrophages and that recruited macrophages affect neutrophil functions, there may be various degrees of interaction between tumor-associated macrophages and tumor-associated neutrophils. Platelets also play an important role in the recruitment and regulation of monocytic and granulocytic cells in the tumor tissues, suggesting that platelet function may be essential for generation of tumor-associated macrophages and tumor-associated neutrophils. In this review, we will explore the biology of tumor-associated macrophages and tumor-associated neutrophils and their possible interactions in the tumor microenvironment. Special attention will be given to the recruitment and activation of these tumor-associated cells and to the roles they play in maintenance of the tumor microenvironment and progression of tumors.

Role of platelets in cancer and cancer-associated thrombosis: Experimental and clinical evidences

The primary hemostatic function of platelets has been recognized for more than a century, but increasing experimental and clinical evidences suggest that platelets are also important mediators of cancer. Cancer indeed influences platelet physiology, and activated platelets participate in each step of cancer development by promoting tumor growth, angiogenesis, metastasis, and cancer-associated thrombosis. Based on both the results of numerous experimental models addressing the involvement of platelets in cancer progression and the results of epidemiologic studies on the use of anti-platelet drugs to prevent cancer, platelets have been proposed as a potential target to reduce the short-term risk of cancer, cancer dissemination and cancer mortality. However, the cancer-associated thrombosis and the risk of bleeding due to anti-platelet drugs are not enough evaluated in experimental models. Therefore, the interesting contribution of platelets to cancer and cancer-associated thrombosis requires the standardization of preclinical and clinical models.

Platelets in cancer. From basic research to therapeutic implications

Platelets are well-known for their major role in primary hemostasis and thrombosis. Cancer patients frequently manifest thrombotic events and present abnormalities in blood coagulation which appear to be linked to altered platelet function and turnover. Moreover, numerous studies indicate an intimate cross-talk between platelets and tumor growth, angiogenesis and metastatic dissemination. Finally, several experimental data and clinical trials suggest possible benefits of anti-platelet drugs on some cancers. Here, we will review the current state of basic biological research regarding the role of platelets in cancer progression. We also critically review the possible clinical applicability of some anti-platelet therapies to limit tumor growth and prevent metastatic dissemination.

Process of hepatic metastasis from pancreatic cancer: biology with clinical significance

PURPOSE

Pancreatic cancer shows a remarkable preference for the liver to establish secondary tumors. Selective metastasis to the liver is attributed to the development of potential microenvironment for the survival of pancreatic cancer cells. This review aims to provide a full understanding of the hepatic metastatic process from circulating pancreatic cancer cells to their settlement in the liver, serving as a basic theory for efficient prediction and treatment of metastatic diseases.

METHODS

A systematic search of relevant original articles and reviews was performed on PubMed, EMBASE and Cochrane Library for the purpose of this review.

RESULTS

Three interrelated phases are delineated as the contributions of the interaction between pancreatic cancer cells and the liver to hepatic metastasis process. Chemotaxis of disseminated pancreatic cancer cells and simultaneous defensive formation of platelets or neutrophils facilitate specific metastasis toward the liver. Remodeling of extracellular matrix and stromal cells in hepatic lobules and angiogenesis induced by proangiogenic factors support the survival and growth of clinical micrometastasis colonizing the liver. The bimodal role of the immune system or prevalence of cancer cells over the immune system makes metastatic progression successfully proceed from micrometastasis to macrometastasis.

CONCLUSIONS

Pancreatic cancer is an appropriate research object of cancer metastasis representing more than a straight cascade. If any of the successive or simultaneous phases, especially tumor-induced immunosuppression, is totally disrupted, hepatic metastasis will be temporarily under control or even cancelled forever. To shrink cancers on multiple fronts and prolong survival for patients, novel oral or intravenous anti-cancer agents covering one or different phases of metastatic pancreatic cancer are expected to be integrated into innovative strategies on the premise of safety and efficacious biostability.

RANK-mediated signaling network and cancer metastasis

Cancer metastasis is highly inefficient and complex. Common features of metastatic cancer cells have been observed using cancer cell lines and genetically reconstituted mouse and human tumor xenograft models. These include cancer cell interaction with the tumor microenvironment and the ability of cancer cells to sense extracellular stimuli and adapt to adverse growth conditions. This review summarizes the coordinated response of cancer cells to soluble growth factors, such as RANKL, by a unique feed forward mechanism employing coordinated upregulation of RANKL and c-Met with downregulation of androgen receptor. The RANK-mediated signal network was found to drive epithelial to mesenchymal transition in prostate cancer cells, promote osteomimicry and the ability of prostate cancer cells to assume stem cell and neuroendocrine phenotypes, and confer the ability of prostate cancer cells to home to bone. Prostate cancer cells with activated RANK-mediated signal network were observed to recruit and even transform the non-tumorigenic prostate cancer cells to participate in bone and soft tissue colonization. The coordinated regulation of cancer cell invasion and metastasis by the feed forward mechanism involving RANKL, c-Met, transcription factors, and VEGF-neuropilin could offer new therapeutic opportunities to target prostate cancer bone and soft tissue metastases.

Mechanistic explanation for platelet contribution to cancer metastasis

Cancer-associated mortality is frequently caused by metastasis, however, our understanding of this process remains incomplete and therapeutic options are limited. Metastasis is a dynamic multi-step process involving intravasation of tumor cells into the host's blood and lymphatic vessels, their dissemination within the circulation, and finally arrest and extravasation in a distant organ where they establish secondary tumors. It is generally conceived that platelets contribute to all steps of hematogenous tumor dissemination. In this review, we provide an overview of the current knowledge of the platelet receptors involved in tumor cell-induced platelet aggregation, an essential immune surveillance escape mechanism of circulating tumor cells. We discuss how platelets prevent immunological attack, contribute to tumor cell extravasation and thereby facilitate colonization of distant organs.

Evaluation of antitumor activity of platelet microbicidal protein on the model of transplanted breast cancer in CBRB-Rb(8.17)1Iem mice

Breast cancer is the most common women's cancer in the world. There is considerable current interest in developing anticancer agents with a new mode of action because of the development of resistance by cancer cells towards current anticancer drugs. Mamalian cells have been shown to contain small, cationic, microbicidal peptides. Antimicrobial peptides have drawn attention as a promising alternative to current antitumor agents. Such peptides have been isolated both from animal and human platelets and have been termed platelets microbicidal proteins (PMP). The aim of this work was to study antitumor activity of PMP in vivo on the model of mouse breast cancer in comparison with antitumor hexapeptide Arg-alpha-Asp-Lys-Val-Tyr-Arg (Immunofan). We demonstrated that the tumors treated with PMP were significant smaller than the control groups (P < 0.05). In experiments in vivo using CBRB-Rb(8.17)1Iem mice with transplanted tumors PMP inhibited tumor growth during the treatments and after its discontinuation. These findings indicate that PMP can exert antitumor effects. Therefore, PMP may be used for the development of therapy for the intervention of breast cancer.

Sustaining cancer through addictive ectopic gene activation

PURPOSE OF REVIEW

Systematic genetic and epigenetic alterations occurring in almost all cancer cells result in the ectopic expression of a variety of tissue-specific potent regulatory factors. This review sheds light on a new aspect of cancer based on the integration of the 'out of context' activity of tissue-restricted genes into the biology of cancer cells.

RECENT FINDINGS

A systematic screen for the ectopic activation of tissue-restricted genes in a variety of cancers has revealed that many normally silent genes are expressed in tumours of all origins. This aberrant gene activation not only could be used as a source of biomarkers, but also, in several cases, reveals clear oncogenic mechanisms associated with the corresponding ectopically expressed factors.

SUMMARY

The characteristic of all cancer cells, which systematically reprogram tissue-specific gene expression and activate silent genes, can be exploited to develop new anticancer strategies aiming at the detection of malignant states, the prediction of their evolution and drug sensitivity and the discovery of new therapeutic approaches.

Platelets in tumor progression: a host factor that offers multiple potential targets in the treatment of cancer

While platelets are well known to play a central role in hemostasis and thrombosis, there is emerging experimental evidence to suggest that they also mediate tumor cell growth, dissemination, and angiogenesis. An increase in platelet number (thrombocytosis) and activity is seen in patients with a wide spectrum of malignancies, and the former is correlated with a decrease in overall survival and poorer prognosis. Preclinical data suggest that circulating tumor cell partnerships with platelets in the blood facilitate tumor metastases through direct interactions and secreted bioactive proteins. Platelets form aggregates with tumor cells, thereby protecting them from host immune surveillance through physical shielding and induction of "platelet mimicry." There is also laboratory evidence to suggest that activated platelets interact with cancer cells within the tumor microenvironment through paracrine signaling and direct contact, thereby promoting tumor cell growth and survival. For example, platelets release mediators of both tumor angiogenesis and osteoclast resorption. The interplay between platelets and tumor cells is complex and bidirectional with involvement of multiple other components within the tumor microenvironment, including immune cells, endothelial cells, and the extracellular matrix. We review the role of platelets in tumor progression, emphasizing the opportunity these interactions afford to target platelets and platelet function to improve patient outcomes in the cancer prevention and treatment setting.

Paraneoplastic thrombocytosis: the secrets of tumor self-promotion

Paraneoplastic thrombocytosis is associated with many solid tumors and often correlates with reduced survival. Recent studies suggest that a pathogenic feed back loop may be operative between platelets and tumor cells, with reciprocal interactions between tumor growth/metastasis and thrombocytosis/platelet activation. Specific molecular pathways have been identified in which tumors can stimulate platelet production and activation; activated platelets can, in turn, promote tumor growth and metastasis. Taken together, these findings provide exciting new potential targets for therapeutic intervention.

Should EMT of Cancer Cells Be Understood as Epithelial-Myeloid Transition?

Cancer cells express epithelial markers, and when progressing in malignancy they may express markers of the mesenchymal cell type. Therefore an epithelial-mesenchymal transition of the cancer cells is assumed. However the mesenchymal markers can equally well be interpreted as myeloid markers since they are common in both types of cell lineages. Moreover, cancer cells express multiple specific markers of the myeloid lineages thus giving rise to the hypothesis that the transition of cancer cells may be from epithelial to myeloid cells and not to mesenchymal cells. This interpretation would better explain why cancer cells, often already in their primary cancer site, frequently show properties common to those of macrophages, platelets and pre-/osteoclasts.

Prognostic significance of thrombocytosis, platelet parameters and aggregation rates in epithelial ovarian cancer

AIM

The aim of this study is to investigate the impact of preoperative platelet counts, parameters and aggregation rates (maximal aggregation rate: MAR) on prognosis in patients with epithelial ovarian cancer (EOC).

METHODS

Preoperative platelet count, parameters and MAR in 182 EOC patients, 122 patients with benign ovarian tumor and 150 healthy women were retrospectively analyzed. The correlation between thrombocytosis, platelet parameters, MAR and clinicopathological factors were evaluated in EOC.

RESULTS

Forty-five (24.73%) EOC patients had preoperative thrombocytosis in this study. The mean platelet count in the EOC group was significantly higher than that of benign and healthy groups (P < 0.001). The MAR in the EOC group was significantly higher than that in the healthy group (71.96% vs 57.03%, P = 0.025). The platelet parameters (mean platelet volume, platelet distribution width, thrombocytocrit and large platelet ratio) were consistently higher in the EOC group than those in the benign and healthy groups, but the differences were insignificant. A significant correlation between thrombocytosis and MAR was observed in EOC patients (r = 0.694, P < 0.001). EOC patients with thrombocytosis were found to have significantly higher grade (P = 0.048), more advanced stage (P = 0.045), higher level carbohydrate antigen-125 (P = 0.007) and greater likelihood of suboptimal cytoreduction (P = 0.035). EOC patients with both thrombocytosis and high MAR were found to have shorter progression-free survival (P = 0.001)and overall survival (P = 0.004). The combination of thrombocytosis and MAR, as well as stage and optimal cytoreduction, retained significance as an independent prognostic factor for overall survival.

CONCLUSION

Thrombocytosis, accompanied by increasing of platelet aggregation rates, is associated with more aggressive tumor biology in EOC. The combination of thrombocytosis and MAR is an independent negative prognostic factor for overall survival in EOC patients.

Radiosensitivity of human prostate cancer cells can be modulated by inhibition of 12-lipoxygenase

Nearly 30% of prostate cancer (PCa) patients treated with potentially curative doses relapse at the sites of irradiation. How some tumor cells acquire radioresistance is poorly understood. The platelet-type 12-lipoxygenases (12-LOX)-mediated arachidonic acid metabolism is important in PCa progression. Here we show that 12-LOX confers radioresistance upon PCa cells. Treatment with 12-LOX inhibitors baicalein or BMD122 sensitizes PCa cells to radiation, without radiosensitizing normal cells. 12-LOX inhibitors and radiation, when combined, have super additive or synergistic inhibitory effects on the colony formation of both androgen-dependent LNCaP and androgen-independent PC-3 PCa cells. In vivo, the combination therapy significantly reduced tumor growth.

A platelet-mimetic paradigm for metastasis-targeted nanomedicine platforms

There is compelling evidence that, beyond their traditional role in hemostasis and thrombosis, platelets play a significant role in mediating hematologic mechanisms of tumor metastasis by directly and indirectly interacting with pro-metastatic cancer cells. With this rationale, we hypothesized that platelets can be an effective paradigm to develop nanomedicine platforms that utilize platelet-mimetic interaction mechanisms for targeted diagnosis and therapy of metastatic cancer cells. Here we report on our investigation of the development of nanoconstructs that interact with metastatic cancer cells via platelet-mimetic heteromultivalent ligand-receptor pathways. For our studies, pro-metastatic human breast cancer cell line MDA-MB-231 was studied for its surface expression of platelet-interactive receptors, in comparison to another low-metastatic human breast cancer cell line, MCF-7. Certain platelet-interactive receptors were found to be significantly overexpressed on the MDA-MB-231 cells, and these cells showed significantly enhanced binding interactions with active platelets compared to MCF-7 cells. Based upon these observations, two specific receptor interactions were selected, and corresponding ligands were engineered onto the surface of liposomes as model nanoconstructs, to enable platelet-mimetic binding to the cancer cells. Our model platelet-mimetic liposomal constructs showed enhanced targeting and attachment of MDA-MB-231 cells compared to the MCF-7 cells. These results demonstrate the promise of utilizing platelet-mimetic constructs in modifying nanovehicle constructs for metastasis-targeted drug as well as modifying surfaces for ex-vivo cell enrichment diagnostic technologies.

Demonstration of a melanoma-specific CD44 alternative splicing pattern that remains qualitatively stable, but shows quantitative changes during tumour progression

The role of CD44 in the progression of human melanoma has mostly been characterised by qualitative changes in expression of its individual variable exons. These exons however, may be expressed to form a number of molecules, the alternative splice variants of CD44, which may be structurally and functionally different. Using real-time PCR measurements with variable exon specific primers we have determined that all are expressed in human melanoma. To permit comparison between different tumours we identified a stable CD44 variable exon (CD44v) expression pattern, or CD44 ‘fingerprint’. This was found to remain unchanged in melanoma cell lines cultured in different matrix environments. To evaluate evolution of this fingerprint during tumour progression we established a scid mouse model, in which the pure expression pattern of metastatic primary tumours, circulating cells and metastases, non-metastatic primary tumours and lung colonies could be studied. Our analyses demonstrated, that although the melanoma CD44 fingerprint is qualitatively stable, quantitative changes are observed suggesting a possible role in tumour progression.

The platelet contribution to cancer progression

Traditionally viewed as major cellular components in hemostasis and thrombosis, the contribution of platelets to the progression of cancer is an emerging area of research interest. Complex interactions between tumor cells and circulating platelets play an important role in cancer growth and dissemination, and a growing body of evidence supports a role for physiologic platelet receptors and platelet agonists in cancer metastases and angiogenesis. Platelets provide a procoagulant surface facilitating amplification of cancer-related coagulation, and can be recruited to shroud tumor cells, thereby shielding them from immune responses, and facilitate cancer growth and dissemination. Experimental blockade of key platelet receptors, such as GP1b/IX/V, GPIIbIIIa and GPVI, has been shown to attenuate metastases. Platelets are also recognized as dynamic reservoirs of proangiogenic and anti-angiogenic proteins that can be manipulated pharmacologically. A bidirectional relationship between platelets and tumors is also seen, with evidence of 'tumor conditioning' of platelets. The platelet as a reporter of malignancy and a targeted delivery system for anticancer therapy has also been proposed. The development of platelet inhibitors that influence malignancy progression and clinical testing of currently available antiplatelet drugs represents a promising area of targeted cancer therapy.

Crosstalk between protease-activated receptor 1 and platelet-activating factor receptor regulates melanoma cell adhesion molecule (MCAM/MUC18) expression and melanoma metastasis

The cellular and molecular pathways that regulate platelet activation, blood coagulation, and inflammation are emerging as critical players in cancer progression and metastasis. Here, we demonstrate a novel signaling mechanism whereby protease-activated receptor 1 (PAR1) mediates expression of melanoma cell adhesion molecule MCAM/MUC18 (MUC18), a critical marker of melanoma metastasis, via activation of platelet-activating factor receptor (PAFR) and cAMP-responsive element-binding protein (CREB). We found that PAR1 silencing with small hairpin RNA inhibits MUC18 expression in metastatic melanoma cells by inhibiting CREB phosphorylation, activity, and binding to the MUC18 promoter. We further demonstrate that the PAF/PAFR pathway mediates MUC18 expression downstream of PAR1. Indeed, PAR1 silencing down-regulates PAFR expression and PAF production, PAFR silencing blocks MUC18 expression, and re-expression of PAFR in PAR1-silenced cells rescues MUC18 expression. We further demonstrate that the PAR1-PAFR-MUC18 pathway mediates melanoma cell adhesion to microvascular endothelial cells, transendothelial migration, and metastatic retention in the lungs. Rescuing PAFR expression in PAR1-silenced cells fully restores metastatic phenotype of melanoma, indicating that PAFR plays critical role in the molecular mechanism of PAR1 action. Our results link the two pro-inflammatory G-protein-coupled receptors, PAR1 and PAFR, with the metastatic dissemination of melanoma and suggest that PAR1, PAFR, and MUC18 are attractive therapeutic targets for preventing melanoma metastasis.

Platelet glycoprotein VI facilitates experimental lung metastasis in syngenic mouse models

BACKGROUND

Glycoprotein (GP)VI is a key receptor for collagen on the platelet surface. It is a member of the immunoglobulin superfamily and is uniquely expressed on the surface of platelets, where it is assembled with the immunoreceptor tyrosine activation motif subunit, FcR-gamma. We have previously reported the generation of a murine model of GPVI deficiency that revealed profound defects in collagen-induced platelet aggregation and in platelet activation following adhesion to collagen. Beyond the hemostasis/thrombosis paradigm, platelet receptors are emerging as significant participants in tumorigenesis and inflammation.

OBJECTIVE

In the current study, we have evaluated a role for platelet GPVI in primary tumor growth and experimental metastasis.

METHODS

Primary tumor induction and experimental metastasis assays were performed using syngenic immunocompetent animals and tumor cells derived from the C57BL/6J mouse strain in wild-type (C57BL/6J) and N10 C57BL/6J congenic GPVI-deficient mice.

RESULTS

Using either a Lewis lung carcinoma (D121) or melanoma (B16F10.1) cell line, we observed an approximately 50% reduction in the number of visible tumor foci in GPVI-deficient mice as compared with control C57BL/6J mice. Additional studies were performed to compare the size of subcutaneously implanted tumor cells, that is, primary tumor growth. Here, we observed no noticeable size difference when comparing the presence or absence of platelet GPVI.

CONCLUSIONS

The results demonstrate that the presence of platelet GPVI facilitates experimental tumor metastasis but does not contribute to the growth of primary tumors.

Inflammation and melanoma metastasis

Metastatic melanoma is extremely refractory to existing chemotherapeutic drugs and bioimmune adjuvant therapies, and the life span of patients with metastatic melanoma is often measured in months. Understanding the mechanisms responsible for the development of tumor metastasis is critical for finding successful curative measures. An expending amount of data reveal the importance of inflammatory microenvironment and stroma in cancer initiation and progression, which brings new directions and approaches to cancer treatment. This review will summarize current data on the role of the tumor microenvironment in shaping the metastatic phenotype of melanoma.

Lipoxygenase metabolism: roles in tumor progression and survival

The metabolism of arachidonic acid through lipoxygenase pathways leads to the generation of various biologically active eicosanoids. The expression of these enzymes vary throughout the progression of various cancers, and thereby they have been shown to regulate aspects of tumor development. Substantial evidence supports a functional role for lipoxygenase-catalyzed arachidonic and linoleic acid metabolism in cancer development. Pharmacologic and natural inhibitors of lipoxygenases have been shown to suppress carcinogenesis and tumor growth in a number of experimental models. Signaling of hydro[peroxy]fatty acids following arachidonic or linoleic acid metabolism potentially effect diverse biological phenomenon regulating processes such as cell growth, cell survival, angiogenesis, cell invasion, metastatic potential and immunomodulation. However, the effects of distinct LOX isoforms differ considerably with respect to their effects on both the individual mechanisms described and the tumor being examined. 5-LOX and platelet type 12-LOX are generally considered pro-carcinogenic, with the role of 15-LOX-1 remaining controversial, while 15-LOX-2 suppresses carcinogenesis. In this review, we focus on the molecular mechanisms regulated by LOX metabolism in some of the major cancers. We discuss the effects of LOXs on tumor cell proliferation, their roles in cell cycle control and cell death induction, effects on angiogenesis, migration and the immune response, as well as the signal transduction pathways involved in these processes. Understanding the molecular mechanisms underlying the anti-tumor effect of specific, or general, LOX inhibitors may lead to the design of biologically and pharmacologically targeted therapeutic strategies inhibiting LOX isoforms and/or their biologically active metabolites, that may ultimately prove useful in the treatment of cancer, either alone or in combination with conventional therapies.

Platelet activation during tumor development, the potential role of BDNF-TrkB autocrine loop

Platelets are an important place for the storage of angiogenic factors, such as vascular endothelial growth factor (VEGF) and brain-derived neurotrophic factor (BDNF). The present study aims to investigate the interaction between BDNF-TrkB pathway and platelet activation during tumor development. In an orthotopic hepatocellular carcinoma (HCC) model, increased levels of serum and plasma BDNF were detected with tumor progression. Higher numbers of CD62P+ and TrkB+ platelets were found in the tumor-bearing rats. In the in vitro setting, tumor-conditioned-medium (TCM) and BDNF recombinant protein stimulated CD62P upregulation and subsequent BDNF release in the freshly isolated platelets, whereas this effect could be inhibited by TrkB blockade. TCM and BDNF culture augmented the expression of heat shock protein 90 (Hsp90) in the platelets, which could be reversed by TrkB blockade. In conclusion, this study suggested the presence of BDNF-TrkB autocrine loop in platelets and its importance in regulating platelet activation during tumor development.

Synthetic curcuminoids modulate the arachidonic acid metabolism of human platelet 12-lipoxygenase and reduce sprout formation of human endothelial cells

Platelet 12-lipoxygenase (P-12-LOX) is overexpressed in different types of cancers, including prostate cancer, and the level of expression is correlated with the grade of this cancer. Arachidonic acid is metabolized by 12-LOX to 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], and this biologically active metabolite is involved in prostate cancer progression by modulating cell proliferation in multiple cancer-related pathways inducing angiogenesis and metastasis. Thus, inhibition of P-12-LOX can reduce these two processes. Several lipoxygenase inhibitors are known, including plant and mammalian lipoxygenases, but only a few of them are known inhibitors of P-12-LOX. Curcumin is one of these lipoxygenase inhibitors. Using a homology model of the three-dimensional structure of human P-12-LOX, we did computational docking of synthetic curcuminoids (curcumin derivatives) to identify inhibitors superior to curcumin. Docking of the known inhibitors curcumin and NDGA to P-12-LOX was used to optimize the docking protocol for the system in study. Over 75% of the compounds of interest were successfully docked into the active site of P-12-LOX, many of them sharing similar binding modes. Curcuminoids that did not dock into the active site did not inhibit P-12-LOX. From a set of the curcuminoids that were successfully docked and selected for testing, two were found to inhibit human lipoxygenase better than curcumin. False-positive curcuminoids showed high LogP (theoretical) values, indicating poor water solubility, a possible reason for lack of inhibitory activity or/and nonrealistic binding. Additionally, the curcuminoids inhibiting P-12-LOX were tested for their ability to reduce sprout formation of endothelial cells (in vitro model of angiogenesis). We found that only curcuminoids inhibiting human P-12-LOX and the known inhibitor NDGA reduced sprout formation. Only limited inhibition of sprout formation at approximately IC(50) concentrations has been seen. At IC(50), a substantial amount of 12-HETE can be produced by lipoxygenase, providing a stimulus for angiogenic sprouting of endothelial cells. Increasing the concentration of lipoxygenase inhibitors above IC(50), thus decreasing the concentration of 12(S)-HETE produced, greatly reduced sprout formation for all inhibitors tested. This universal event for all tested lipoxygenase inhibitors suggests that the inhibition of sprout formation was most likely due to the inhibition of human P-12-LOX but not other cancer-related pathways.

Ligand-mimetic anti-aIIbβ3 antibody PAC-1 inhibits tyrosine signaling, proliferation and lung colonization of melanoma cells

Beta3 integrin expression is the hallmark of melanoma and may serve as a potential therapeutic target. While alphav beta3 integrin expression seems to be constitutive in melanoma, ectopic expression of platelet-alphaIIb beta3 is dependent on progression. B16a murine melanoma is a suitable model for studies on alphaIIb beta3 treatment strategies since alphav beta3 is not expressed in this cell line. Here we have used a ligand-mimetic anti-alphaIIb beta3 monoclonal antibody, PAC-1, to test the biological consequences of alphaIIb beta3 modulation in melanoma cells. We have previously reported that in B16a cells FAK is constitutively active and tyrosine-phosphorylated. Upon PAC-1 binding to the surface alphaIIb beta3, which is in the active conformation, FAK became dephosphorylated through a process of PKC-dependent phosphatase activation. Furthermore, PAC-1 binding to B16a cells induced a significant decrease in phosphotyrosine-positive melanoma cells within 30 min. Treatment of B16a cells in vitro with PAC-1 significantly inhibited proliferation by decreasing the mitotic index but not affecting apoptotic rate. Incubation of B16a cells with PAC-1 decreased their lung colonization potential, suggesting a profound alteration in their biological behavior under the effect of this antibody. These preclinical data suggest that the ectopic expression of alphaIIb beta3 in melanoma cells can be exploited as a novel target of antibody therapy of melanoma.