Emerging Roles of PAR-1 and PAFR in Melanoma Metastasis

Melanoma growth, angiogenesis and metastatic progression are strongly promoted by the inflammatory tumor microenvironment due to high levels of cytokine and chemokine secretion by the recruited inflammatory and stromal cells. In addition, platelets and molecular components of procoagulant pathways have been recently emerging as critical players of tumor growth and metastasis. In particular, thrombin, through the activity of its receptor protease-activated receptor-1 (PAR-1), regulates tumor cell adhesion to platelets and endothelial cells, stimulates tumor angiogenesis, and promotes tumor growth and metastasis. Notably, in many tumor types including melanoma, PAR-1 expression directly correlates with their metastatic phenotype and is directly responsible for the expression of interleukin-8, matrix metalloproteinase-2 (MMP-2), vascular endothelial growth factor, platelet-derived growth factor, and integrins. Another proinflammatory receptor–ligand pair, platelet-activating factor (PAF) and its receptor (PAFR), have been shown to act as important modulators of tumor cell adhesion to endothelial cells, angiogenesis, tumor growth and metastasis. PAF is a bioactive lipid produced by a variety of cells from membrane glycerophospholipids in the same reaction that releases arachidonic acid, and can be secreted by platelets, inflammatory cells, keratinocytes and endothelial cells. We have demonstrated that in metastatic melanoma cells, PAF stimulates the phosphorylation of cyclic adenosine monophosphate response element-binding protein (CREB) and activating transcription factor 1 (ATF-1), which results in overexpression of MMP-2 and membrane type 1-MMP (membrane type 1-MMP). Since only metastatic melanoma cells overexpress CREB/ATF-1, we propose that metastatic melanoma cells are better equipped than their non-metastatic counterparts to respond to PAF within the tumor microenvironment. The evidence supporting the hypothesis that the two G-protein coupled receptors, PAR-1 and PAFR, contribute to the acquisition of the metastatic phenotype of melanoma is presented and discussed

An association between anti-platelet drug use and reduced cancer prevalence in diabetic patients: results from the Vermont Diabetes Information System Study

<p>Abstract</p> <p>Background</p> <p>Diabetes is associated with an increased risk of several malignancies. Both diabetic patients and patients with cancer have an increase in platelet reactivity and platelet activation has recently emerged as a potential mediator of cancer progression. Drug therapies, such as aspirin, that reduce platelet reactivity reduce both cardiovascular and cancer risk.</p> <p>Methods</p> <p>We performed a cross-sectional analysis to assess the association between history of cancer and current anti-platelet drug use in a primary care population of adults with diabetes enrolled in the Vermont Diabetes Information System.</p> <p>Results</p> <p>Self-reported characteristics, medical history, and a complete medication list were recorded on 1007 diabetic adults. Fifty percent of diabetic patients used an anti-platelet drug. In unadjusted analysis, no association was seen between anti-platelet drug use and cancer history (OR = 0.93; <it>P </it>= .70). Platelet inhibitor use was associated with a decreased patient-reported history of malignancy in a multivariate logistic regression adjusted for age, sex, body mass index, comorbidity, and number of medications (OR = 0.66; CI 0.44-0.99; <it>P </it>= .045). Similar odds of association were seen in both males and females, and for aspirin and non-aspirin platelet inhibitor therapy.</p> <p>Conclusions</p> <p>Our data suggest an association between anti-platelet drug use and reduced cancer prevalence in patients with diabetes. Given the potentially large implications of our observations in the diabetic population, further studies are required to determine if this association is causal.</p

PAR1 is selectively over expressed in high grade breast cancer patients: a cohort study

<p>Abstract</p> <p>Background</p> <p>The protease-activated receptor (PAR1) expression is correlated with the degree of invasiveness in cell lines. Nevertheless it has never been directed involved in breast cancer patients progression. The aim of this study was to determine whether PAR1 expression could be used as predictor of metastases and mortality.</p> <p>Methods</p> <p>In a cohort of patients with infiltrating ductal carcinoma studied longitudinally since 1996 and until 2007, PAR1 over-expression was assessed by immunoblotting, immunohistochemistry, and flow citometry. Chi-square and log rank tests were used to determine whether there was a statistical association between PAR1 overexpression and metastases, mortality, and survival. Multivariate analysis was performed including HER1, stage, ER and nodes status to evaluate PAR1 as an independent prognostic factor.</p> <p>Results</p> <p>Follow up was 95 months (range: 2–130 months). We assayed PAR1 in a cohort of patients composed of 136 patients; we found PAR1 expression assayed by immunoblotting was selectively associated with high grade patients (50 cases of the study cohort; P = 0.001). Twenty-nine of 50 (58%) patients overexpressed PAR1, and 23 of these (46%) developed metastases. HER1, stage, ER and PAR1 overexpression were robustly correlated (Cox regression, P = 0.002, P = 0.024 and P = 0.002 respectively). Twenty-one of the 50 patients (42%) expressed both receptors (PAR1 and HER1 P = 0.0004). We also found a statistically significant correlation between PAR1 overexpression and increased mortality (P = 0.0001) and development of metastases (P = 0.0009).</p> <p>Conclusion</p> <p>Our data suggest PAR1 overexpression may be involved in the development of metastases in breast cancer patient and is associated with undifferentiated cellular progression of the tumor. Further studies are needed to understand PAR1 mechanism of action and in a near future assay its potential use as risk factor for metastasis development in high grade breast cancer patients.</p

Enhanced Platelet Activation Mediates the Accelerated Angiogenic Switch in Mice Lacking Histidine-Rich Glycoprotein

BACKGROUND: The heparin-binding plasma protein histidine-rich glycoprotein (HRG; alternatively, HRGP/HPRG) can suppress tumor angiogenesis and growth in vitro and in vivo. Mice lacking the HRG gene are viable and fertile, but have an enhanced coagulation resulting in decreased bleeding times. In addition, the angiogenic switch is significantly enhanced in HRG-deficient mice. METHODOLOGY/PRINCIPAL FINDINGS: To address whether HRG deficiency affects tumor development, we have crossed HRG knockout mice with the RIP1-Tag2 mouse, a well established orthotopic model of multistage carcinogenesis. RIP1-Tag2 HRG(-/-) mice display significantly larger tumor volume compared to their RIP1-Tag2 HRG(+/+) littermates, supporting a role for HRG as an endogenous regulator of tumor growth. In the present study we also demonstrate that platelet activation is increased in mice lacking HRG. To address whether this elevated platelet activation contributes to the increased pathological angiogenesis in HRG-deficient mice, they were rendered thrombocytopenic before the onset of the angiogenic switch by injection of the anti-platelet antibody GP1bα. Interestingly, this treatment suppressed the increase in angiogenic neoplasias seen in HRG knockout mice. However, if GP1bα treatment was initiated at a later stage, after the onset of the angiogenic switch, no suppression of tumor growth was detected in HRG-deficient mice. CONCLUSIONS: Our data show that increased platelet activation mediates the accelerated angiogenic switch in HRG-deficient mice. Moreover, we conclude that platelets play a crucial role in the early stages of tumor development but are of less significance for tumor growth once angiogenesis has been initiated

The activation of Proteinase-Activated Receptor-1 (PAR1) mediates gastric cancer cell proliferation and invasion

<p>Abstract</p> <p>Background</p> <p>In addition to regulating platelet function, the G protein-coupled sub-family member Proteinase-activated receptor-1 (PAR1) has a proposed role in the development of various cancers, but its exact role and mechanism of action in the invasion, metastasis, and proliferation process in gastric cancer have yet to be completely elucidated. Here, we analyzed the relationship between PAR1 activation, proliferation, invasion, and the signaling pathways downstream of PAR1 activation in gastric cancer.</p> <p>Methods</p> <p>We established a PAR1 stably transfected MKN45 human gastric cancer cell line (MKN45/PAR1) and performed cell proliferation and invasion assays employing this cell line and MKN28 cell line exposed to PAR1 agonists (α-thrombin and TFLLR-NH₂). We also quantified NF-κB activation by electrophoretic mobility shift assay (EMSA) and the level of Tenascin-C (TN-C) expression in conditioned medium by ELISA of MKN45/PAR1 following administration of α-thrombin. A high molecular weight concentrate was derived from the resultant conditioned medium and subsequent cultures of MKN45/PAR1 and MKN28 were exposed to the resultant concentrate either in the presence or absence of TN-C-neutralizing antibody. Lysates of these subsequent cells were probed to quantify levels of phospholyrated Epidermal Growth Factor Receptor (EGFR).</p> <p>Result</p> <p>PAR1 in both PAR1/MKN45 and MKN28 was activated by PAR1 agonists, resulting in cell proliferation and matrigel invasion. We have shown that activation of NF-κB and EGFR phosphorylation initially were triggered by the activation of PAR1 with α-thrombin. Quantitative PCR and Western blot assay revealed up-regulation of mRNA and protein expression of NF-κB target genes, especially TN-C, a potential EGFR activator. The suppressed level of phosphorylated EGFR, observed in cells exposed to concentrate of conditioned medium in the presence of TN-C-neutralizing antibody, identifies TN-C as a putative autocrine stimulatory factor of EGFR possibly involved in the sustained PAR1 activation responses observed.</p> <p>Conclusion</p> <p>Our data indicate that in gastric carcinoma cells, PAR1 activation can trigger an array of responses that would promote tumor cell growth and invasion. Over expression of NF-κB, EGFR, and TN-C, are among the effects of PAR1 activation and TN-C induces EGFR activation in an autocrine manner. Thus, PAR1 is a potentially important therapeutic target for the treatment of gastric cancer.</p

Aptamers as molecular recognition elements for electrical nanobiosensors

Recent advances in nanotechnology have enabled the development of nanoscale sensors that outperform conventional biosensors. This review summarizes the nanoscale biosensors that use aptamers as molecular recognition elements. The advantages of aptamers over antibodies as sensors are highlighted. These advantages are especially apparent with electrical sensors such as electrochemical sensors or those using field-effect transistors

Revisiting perioperative chemotherapy: the critical importance of targeting residual cancer prior to wound healing

<p>Abstract</p> <p>Background</p> <p>Scientists and physicians have long noted similarities between the general behavior of a cancerous tumor and the physiological process of wound healing. But it may be during metastasis that the parallels between cancer and wound healing are most pronounced. And more particularly and for the reasons detailed in this paper, any cancer remaining after the removal of a solid tumor, whether found in micrometastatic deposits in the stroma or within the circulation, may be heavily dependent on wound healing pathways for its further survival and proliferation.</p> <p>Discussion</p> <p>If cancer cells can hijack the wound healing process to facilitate their metastatic spread and survival, then the period immediately after surgery may be a particularly vulnerable period of time for the host, as wound healing pathways are activated and amplified after the primary tumor is removed. Given that we often wait 30 days or more after surgical removal of the primary tumor before initiating adjuvant chemotherapy to allow time for the wound to heal, this paper challenges the wisdom of that clinical paradigm, providing a theoretical rationale for administering therapy during the perioperative period.</p> <p>Summary</p> <p>Waiting for wound healing to occur before initiating adjuvant therapies may be seriously compromising their effectiveness, and patients subsequently rendered incurable as a result of this wait. Clinical trials to establish the safety and effectiveness of administering adjuvant therapies perioperatively are needed. These therapies should target not only the residual cancer cells, but also the wound healing pathway utilized by these cells to proliferate and metastasize.</p