Nadia M. Bambace

The platelet contribution to cancer progression

Summary.  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.

The effect of P2Y-mediated platelet activation on the release of VEGF and endostatin from platelets.

Vascular endothelial growth factor (VEGF) and endostatin are key protein modulators of angiogenesis found within platelets. The platelet activation pathways that control angiogenic protein release are incompletely elucidated. The differential release of pro-angiogenic and anti-angiogenic proteins from the platelet has been demonstrated for proteinase activated receptors (PARs). Given the ability of tumors to secrete ADP and the availability of ADP receptor antagonists clinically, we determined the influence of adenosine diphosphate (ADP) and the ADP receptors, P2Y1 and P2Y12, on platelet release of the angiogenic stimulator protein, VEGF, and the angiogenic inhibitor protein, endostatin. Minimally altered whole blood (WB) and platelet rich plasma (PRP) from healthy volunteers was stimulated with ADP alone (12.5 uM), in combination with a P2Y1 antagonist (MRS2179) or a P2Y12 antagonist (cangrelor). VEGF and endostatin protein concentrations were assessed by an ELISA assay. We report that maximally stimulating concentrations of ADP significantly increased VEGF release from platelets in both PRP and WB by 36+/−12% 36+/−12% 54+/−18% 36 ± 12% (p < 0.05) respectively as compared to control. Both P2Y1 and P2Y12 receptor antagonism inhibited this release. Conversely, endostatin levels did not change following ADP stimulation in PRP, while a 4.7% (p = 0.03) increase was observed in WB. As compared to thrombin receptor activation, ADP activation was a weaker stimulus for VEGF release. We found that activation of platelets by ADP results in an increase in soluble VEGF concentrations with minimal effects on endostatin concentrations, suggesting ADP release in the tumor microenvironment may be, on balance, proangiogenic. P2Y receptor antagonism abrogates ADP mediated proangiogenic protein release and thus may represent a potential pharmacologic strategy for regulating platelet mediated angiogenesis.

Efficacy of a short course of complex lymphedema therapy or graduated compression stocking therapy in the treatment of post-thrombotic syndrome

Treatment options for established post-thrombotic syndrome (PTS) are limited. Complex lymphedema therapy (CLT), a non-invasive treatment that improves lymphatic flow, may have the potential to improve PTS. We conducted a single-center, investigator-blind, randomized controlled trial of 31 patients with a clinically established diagnosis of PTS and compared the efficacy of graduated compression stockings alone (30–40 mmHg) with CLT, a treatment that includes compression stockings, exercise, patient education, skin care and lymphatic drainage. Primary outcomes were the 1- and 3-month changes in PTS severity by the Villalta score and disease-specific quality of life using the VEINES-QOL (Venous Insufficiency Epidemiological and Economic Study Quality of Life) questionnaire. Analysis was by intent-to-treat. We found from a baseline average score of 9.9 points, CLT reduced mean PTS severity scores by −2.4 points (p=0.02) at the 1-month and −2.3 points (p=0.05) at the 3-month follow-up. Score reductions with stockings only were similar at −2.1 (p=0.03) and −3.3 points (p=0.03) at 1 and 3 months. The differences in score between treatments were not significant. Neither treatment significantly changed the VEINES-QOL score except in patients with severe disease. Patients with moderate to severe PTS derived the greatest benefit from either therapy and the two therapies differentially impacted PTS signs and symptoms. We found a short course of lymphedema therapy and compression stockings offer similar benefit in patients with PTS; however, larger studies are needed to further explore the potential use of CLT in PTS, particularly in patients with more severe disease. ClinicalTrials.gov Identifier: NCT00633971.

Platelet phenotype changes associated with breast cancer and its treatment.

Abstract Platelets and their granular contents influence both angiogenesis and breast cancer progression. This study was performed to assess the effect of breast cancer and its treatment on platelet biology and the response to inhibition of the platelet P2Y12 receptor. Receptor-specific platelet activation and inhibition was studied for three platelet-associated proteins important in cancer angiogenesis and progression, vascular endothelial growth factor (VEGF), thrombospondin1 (TSP1), and transforming growth factor beta 1 (TGF-β1). Twenty-four women with active breast cancer and 10 healthy controls not receiving antiplatelet therapy participated in the study. Ex vivo activation of platelets in whole blood was accomplished using PAR1AP, PAR4AP, convulxin, and ADP. Platelet inhibition was accomplished using the P2Y12 receptor antagonist cangrelor (the in vitro equivalent of clopidogrel). VEGF, TSP1, and TGF-β1 were measured using standard ELISA. Platelet activation by ADP, PAR1, PAR4, and collagen receptors increased VEGF, TSP1, and TGF-β1 secretion in patients with breast cancer. Agonist-induced release of VEGF was greater in cancer patients as compared to healthy controls (p = 0.02 for ADP, p < 0.001 for PAR1AP, PAR4AP, and convulxin) despite a decrease in the efficiency of VEGF secretion in patients with breast cancer. These differences were not observed for TSP1 and TGF-β1 secretion. P2Y12 receptor inhibition decreased VEGF, TSP1, and TGF-β1 secretion. In patients with cancer, cangrelor inhibited TSP1 release to a greater extent than VEGF and TGF-β1 release. In patients with breast cancer, the magnitude of platelet inhibition achieved by cangrelor was greater than that achieved with healthy controls for all agonists and platelet proteins studied. While platelets are known to influence progression of breast cancer, our results show that breast cancer and its treatment influence the platelet phenotype by increasing the secretion of pro-angiogenic proteins following platelet activation, modulating the efficiency of platelet protein release as well as increasing the response to antiplatelet therapy.