Addition of both platelets and thrombin in combination accelerates tumor cells to adhere to endothelial cells in vitro

Thrombin-unique coagulation system protein with multifaceted impacts on cancer and metastasis

The association between blood coagulation and cancer development is well recognized. Thrombin, the pleiotropic enzyme best known for its contribution to fibrin formation and platelet aggregation during vascular hemostasis, may also trigger cellular events through protease-activated receptors, PAR-1 and PAR-4, leading to cancer progression. Our pioneering findings provided evidence that thrombin contributes to cancer metastasis by increasing adhesive potential of malignant cells. However, there is evidence that thrombin regulates every step of cancer dissemination: (1) cancer cell invasion, detachment from primary tumor, migration; (2) entering the blood vessel; (3) surviving in vasculature; (4) extravasation; (5) implantation in host organs. Recent studies have provided new molecular data about thrombin generation in cancer patients and the mechanisms by which thrombin contributes to transendothelial migration, platelet/tumor cell interactions, angiogenesis, and other processes. Though a great deal is known regarding the role of thrombin in cancer dissemination, there are new data for multiple thrombin-mediated events that justify devoting focus to this topic with a comprehensive approach.

Baicalein inhibits agonist- and tumor cell-induced platelet aggregation while suppressing pulmonary tumor metastasis via cAMP-mediated VASP phosphorylation along with impaired MAPKs and PI3K-Akt activation

Recently, the importance of platelet activation in cancer metastasis has become generally accepted. As a result, the development of new platelet inhibitors with minimal adverse effects is now a promising area of targeted cancer therapy. Baicalein is a functional ingredient derived from the root of Scutellaria baicalensis Georgi, a plant used intraditional medicine. The pharmacological effects of this compound including anti-oxidative and anti-inflammatory activities have already been demonstrated. However, its effects on platelet activation are unknown. We therefore investigated the effects of baicalein on ligand-induced platelet aggregation and pulmonary cancer metastasis. In the present study, baicalein inhibited agonist-induced platelet aggregation, granule secretion markers (P-selectin expression and ATP release), [Ca(2+)]i mobilization, and integrin αIIbβ3 expression. Additionally, baicalein attenuated ERK2, p38, and Akt activation, and enhanced VASP phosphorylation. Indeed, baicalein was shown to directly inhibit PI3K kinase activity. Moreover, baicalein attenuated the platelet aggregation induced by C6 rat glioma tumor cells in vitro and suppressed CT26 colon cancer metastasis in mice. These features indicate that baicalein is a potential therapeutic drug for the prevention of cancer metastasis.

Deadly allies: the fatal interplay between platelets and metastasizing cancer cells

The general notion that functional platelets are important for successful hematogenous tumor metastasis has been inaugurated more than 4 decades ago and has since been corroborated in numerous experimental settings. Thorough preclinical investigations have, at least in part, clarified some specifics regarding the involvement of platelet adhesion receptors, such as thrombin receptors or integrins, in the metastasis cascade. Pivotal preclinical experiments have demonstrated that hematogenous tumor spread was dramatically diminished when platelets were depleted from the circulation or when functions of platelet surface receptors were inhibited pharmacologically or genetically. Such insight has inspired researchers to devise novel antitumoral therapies based on targeting platelet receptors. However, several mechanistic aspects underlying the impact of platelet receptors on tumor metastasis are not fully understood, and agents directed against platelet receptors have not yet found their way into the clinic. In addition, recent results suggesting that targeted inhibition of certain platelet surface receptors may even result in enhanced experimental tumor metastasis have demonstrated vividly that the role of platelets in tumor metastasis is more complex than has been anticipated previously. This review gives a comprehensive overview on the most important platelet receptors and their putative involvement in hematogenous metastasis of malignant tumors.

Thrombin induces tumor growth, metastasis, and angiogenesis: Evidence for a thrombin-regulated dormant tumor phenotype

The association of idiopathic venous thrombosis with occult cancer is generally recognized. However, it has not been fully appreciated that thrombin generated during thrombosis can augment the malignant phenotype. Thrombin activates tumor cell adhesion to platelets, endothelial cells, and subendothelial matrix proteins; enhances tumor cell growth; increases tumor cell seeding and spontaneous metastasis; and stimulates tumor cell angiogenesis. These mechanisms are reviewed. Evidence is also presented to support the hypothesis that thrombin serves to preserve dormant tumor cells in individuals, preventing host eradication. It is proposed that tumor malignancy may be regulated by a procoagulant/anticoagulant axis.

Natural 1-O-alkylglycerols reduce platelet-activating factor-induced release of [3H]-serotonin in rabbit platelets

Natural 1-O-alkylglycerols have multiple biological activities with distinct mechanisms. In THP-1 monocytes, they amplify platelet-activating factor production. In endothelial cells, they participate in the production of 1-O-alkyl-2-acyl-sn-glycerol, a PKC inhibitor. Since PAF as well as PKC may interfere with platelet functions, we studied the effect of natural alkylglycerols purified from shark liver oil on [3H]-serotonin release from rabbit platelets in vitro. [3H]-alkylglycerols (1 microM) were consistently incorporated into platelet lipids and after a 2-h incubation, they were metabolised into phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, which represented 53.5+/-1.7%, 36.3+/-1.8%, 5.3+/-0.5% of metabolised [3H]-alkylglycerols, respectively. Alkylglycerols (10 microM) had no effect on spontaneous [3H]-serotonin release. However, alkylglycerols partially inhibited PAF-induced [3H]-serotonin release while they did not modify thrombin-induced release. These data show that alkylglycerols inhibit partially and specifically PAF-induced platelet stimulation and suggest that this effect could result from interfering with PAF receptors.

Thrombocytosis is associated with a significant increase in the cancer specific death rate after radical nephrectomy

PURPOSE

We have previously reported that patients with advanced renal cell carcinoma and a normal platelet count of 400,000/mm. have a 64% increase in life expectancy compared with those with thrombocytosis. We determined whether thrombocytosis was predictive of death from renal cell carcinoma after radical nephrectomy was performed with curative intent for early stage disease.

MATERIALS AND METHODS

We reviewed the records of 204 patients with renal cell carcinoma who underwent radical nephrectomy with curative intent between June 1993 and January 2000 at Emory University Hospital. Survival, pathological grade and stage were recorded from the Emory Winship Cancer Institute tumor registry. Platelet counts were recorded and any patient with at least 1 platelet count of greater than 400,000/mm. was classified with thrombocytosis. Those with a platelet count of 400,000/mm. were classified with a normal platelet count.

RESULTS

There were 26 patients with thrombocytosis and 178 patients with persistently normal platelet counts. The overall and cancer specific death rate in the 26 patients with thrombocytosis was 50% and 42%, respectively. The overall mean time between nephrectomy and death was 12.1 months in this group. The overall and cancer specific death rate in the 178 patients with a normal platelet count was 15.2% and 7.3%, respectively. Mean time to death was 22.6 months in this group. Differences in the overall and cancer specific death rates were highly statistically significant as well as clinically significant. These differences remained significant after controlling for grade, stage and histological type of cancer.

CONCLUSIONS

This study documents the association of thrombocytosis with decreased survival in patients with renal cell carcinoma. In those who undergo nephrectomy for early stage renal cell carcinoma with a perioperative platelet count of greater than 400,000/mm. the cancer specific death rate from renal cell carcinoma is greater than 5 times the rate in patients with a persistently normal platelet counts after radical nephrectomy. The platelet count appears to be a new and powerful independent prognosticator in patients with renal cell carcinoma who undergo radical nephrectomy for presumed localized disease.

Serum vascular endothelial growth factor in patients with head and neck squamous cell carcinoma

Vascular endothelial growth factor (VEGF) is a key pro-angiogenic cytokine expressed by most human tumours. Two isoforms, VEGF121 and VEGF165, are soluble and can be assayed in serum. Serum VEGF has been shown to be significantly raised in patients with solid tumours and shows some promise as a potentially useful tumour marker. Serum levels of VEGF were assayed in 52 patients with untreated head and neck squamous cell carcinoma (HNSCC) and 104 healthy controls. Serum VEGF is significantly raised in patients with HNSCC (P < 0.001), but there was no association with either tumour stage or specifically the presence of nodal metastases. Sixteen patients (31%) had a higher serum VEGF than 95th centile of controls, suggesting that serum VEGF measurement is of little practical use as an initial diagnostic tool. The finding that patients with HNSCC have significantly raised serum VEGF probably relates to enhanced platelet aggregation in these patients.