Platelets and hemophilia: A review of the literature

Efficacy and safety evaluation of eptacog beta (coagulation factor VIIa [recombinant]-jncw) for the treatment of hemophilia A and B with inhibitors

INTRODUCTION

Bypassing agents (BPAs) are used to treat acute bleeding episodes, manage bleeding during perioperative care, and prophylactically minimize bleed occurrence in persons with hemophilia A or B with inhibitors (PwHABI). However, the effectiveness of BPAs that have been prescribed for the last several decades can be variable, motivating the development of a new recombinant activated factor VII, eptacog beta.

AREAS COVERED

This review covers key eptacog beta findings from phase 1b and phase 3 (PERSEPT) clinical trials, which formed the basis for its regulatory approval to treat PwHABI ages 12 and older. Descriptions of eptacog beta structure and glycosylation profile, mechanism of action, preclinical study results, and cost analyses are also presented.

EXPERT OPINION

PwHABI have had only two options for bleed treatment for the past several decades. With its distinct glycosylation profile, eptacog beta offers a novel therapy aiming to improve upon BPAs currently in use, providing an option with more than one dosing regimen and a rapid response that allows most bleeds to be treated with just one dose. This has become particularly important given the use of subcutaneous medications (e.g., emicizumab) for prophylaxis of bleeding. Clinicians should consider eptacog beta as a BPA for all PwHABI.

Proteomic analysis of MSC-derived apoptotic vesicles identifies Fas inheritance to ameliorate haemophilia a via activating platelet functions

Apoptotic vesicles (apoVs) are apoptotic cell-derived nanosized vesicles that play a crucial role in multiple pathophysiological settings. However, their detailed characteristics, specific surface markers, and biological properties are not fully elucidated. In this study, we compared mesenchymal stem cell (MSC)-derived apoVs and exosomes from three different types of MSCs including human bone marrow MSCs (hBMSCs), human adipose MSCs (hASCs), and mouse bone marrow MSCs (mBMSCs). We established a unique protein map of MSC-derived apoVs and identified the differences between apoVs and exosomes in terms of functional protein cargo and surface markers. Furthermore, we identified 13 proteins specifically enriched in apoVs compared to exosomes, which can be used as apoV-specific biomarkers. In addition, we showed that apoVs inherited apoptotic imprints such as Fas to ameliorate haemophilia A in factor VIII knockout mice via binding to the platelets' FasL to activate platelet functions, and therefore rescuing the blood clotting disorder. In summary, we systemically characterized MSC-derived apoVs and identified their therapeutic role in haemophilia A treatment through a previously unknown Fas/FasL linkage mechanism.

Alterations of the Platelet Proteome in Lung Cancer: Accelerated F13A1 and ER Processing as New Actors in Hypercoagulability

Simple Summary

The risk of venous thromboembolism in cancer is nine times higher than in the general population and the second leading cause of death in these patients. Tissue factor and downstream plasmatic coagulation cascade are largely responsible for the risk of thrombosis in cancer. In recent years, it has been increasingly recognised that platelets also play a central role in tumour growth and cancer-associated thrombosis. The underlying molecular mechanisms are largely unknown. In order to comprehensively investigate the biochemical changes in platelets from cancers with high risk of thrombosis, we examined the platelet proteome of brain and lung cancer patients in comparison to sex and age-matched healthy controls. However, we only found alterations in lung cancer, where some of these platelet proteins directly promote thrombosis. One example is the increased amount of the enzyme protein disulfide isomerase, which is clinically investigated as an antithrombotic drug target of the plant-based flavonol quercetin.

Abstract

In order to comprehensively expose cancer-related biochemical changes, we compared the platelet proteome of two types of cancer with a high risk of thrombosis (22 patients with brain cancer, 19 with lung cancer) to 41 matched healthy controls using unbiased two-dimensional differential in-gel electrophoresis. The examined platelet proteome was unchanged in patients with brain cancer, but considerably affected in lung cancer with 15 significantly altered proteins. Amongst these, the endoplasmic reticulum (ER) proteins calreticulin (CALR), endoplasmic reticulum chaperone BiP (HSPA5) and protein disulfide-isomerase (P4HB) were significantly elevated. Accelerated conversion of the fibrin stabilising factor XIII was detected in platelets of patients with lung cancer by elevated levels of a coagulation factor XIII (F13A1) 55 kDa fragment. A significant correlation of this F13A1 cleavage product with plasma levels of the plasmin–α-2-antiplasmin complex and D-dimer suggests its enhanced degradation by the fibrinolytic system. Protein association network analysis showed that lung cancer-related proteins were involved in platelet degranulation and upregulated ER protein processing. As a possible outcome, plasma FVIII, an immediate end product for ER-mediated glycosylation, correlated significantly with the ER-executing chaperones CALR and HSPA5. These new data on the differential behaviour of platelets in various cancers revealed F13A1 and ER chaperones as potential novel diagnostic and therapeutic targets in lung cancer patients.

Decreased platelet surface phosphatidylserine predicts increased bleeding in patients with severe factor VIII deficiency

BACKGROUND

Bleeding phenotypes among individuals with severe factor VIII (FVIII) deficiency are variable, even with routine prophylactic FVIII administration. Activated platelets, in addition to their role in primary hemostasis, play a major role in coagulation by providing a phospholipid surface to which coagulation factors bind.

OBJECTIVES

The aim of this study was to determine whether platelet function is associated with past and/or future bleeding in patients with severe FVIII deficiency on prophylaxis.

PATIENTS/METHODS

Platelet function quantified by platelet surface expression of phosphatidylserine, platelet surface glycoprotein (GP) VI, platelet surface activated GPIIb-IIIa, platelet surface P-selectin, the percentage of coated platelets, and the percentage of platelet-derived microparticles in the presence or absence of in vitro activation by various agonists was assessed in 34 patients.

RESULTS

Decreased platelet surface phosphatidylserine expression (identified by annexin V binding), both in the presence and absence of ADP/thrombin receptor activating peptide, demonstrated a significant association with both prior and subsequent bleeding in any location and specifically with hemarthrosis. No significant difference between patients with and without bleeding was observed in any of the other platelet activity markers.

CONCLUSIONS

Decreased platelet surface phosphatidylserine expression measured by annexin V binding predicts increased bleeding in severe FVIII deficient patients on prophylaxis.

Platelet function and microvesicle generation in patients with hemophilia A

Our results do not support any effect of FVIII on platelet function in patients with severe HA treated under the regime of prophylaxis.

Heterogeneity in Bleeding Tendency and Arthropathy Development in Individuals with Hemophilia

People with hemophilia (PWH) have an increased tendency to bleed, often into their joints, causing debilitating joint disease if left untreated. To reduce the incidence of bleeding events, PWH receive prophylactic replacement therapy with recombinant factor VIII (FVIII) or FIX. Bleeding events in PWH are typically proportional to their plasma FVIII or IX levels; however, in many PWH, bleeding tendency and the likelihood of developing arthropathy often varies independently of endogenous factor levels. Consequently, many PWH suffer repeated bleeding events before correct dosing of replacement factor can be established. Diagnostic approaches to define an individual's bleeding tendency remain limited. Multiple modulators of bleeding phenotype in PWH have been proposed, including the type of disease-causing variant, age of onset of bleeding episodes, plasma modifiers of blood coagulation or clot fibrinolysis pathway activity, interindividual differences in platelet reactivity, and endothelial anticoagulant activity. In this review, we summarize current knowledge of established factors modulating bleeding tendency and discuss emerging concepts of additional biological elements that may contribute to variable bleeding tendency in PWH. Finally, we consider how variance in responses to new gene therapies may also necessitate consideration of patient-specific tailoring of treatment. Cumulatively, these studies highlight the need to reconsider the current "one size fits all" approach to treatment regimens for PWH and consider therapies guided by the bleeding phenotype of each individual PWH at the onset of therapy. Further characterization of the biological bases of bleeding heterogeneity in PWH, combined with the development of novel diagnostic assays to identify those factors that modulate bleeding risk in PWH, will be required to meet these aspirations.

An overview of patients with haemophilia A in China: Epidemiology, disease severity and treatment strategies

INTRODUCTION

Haemophilia A (HA) is a rare X chromosome-linked bleeding disorder resulting in missing or defective clotting factor VIII (FVIII) and causes large disease burden.

AIM

As a member of World Federation of Hemophilia, China seeks to understand the current epidemiology, disease profile and treatment landscape of patients with HA through the Hemophilia Treatment Center Collaboration Network of China (HTCCNC).

METHODS

The HTCCNC enabled data collection on patients with HA from 166 member hospitals (2007-2019) across China. The distribution of patients across 31 divisions was summarized using a heat map. Patient demographics, disease severity and clinical and treatment information were summarized using descriptive statistics.

RESULTS

HTCCNC identified 17,779 patients with HA during 2007-2019. Patients were predominantly male (99.99%), and 28.3% had a known family history of haemophilia. Among patients with lab-measured disease severity (N = 13,116), 6,519 had severe HA (49.7%), 4,788 had moderate HA (36.5%), and 1,809 had mild HA (13.8%). Among patients with information on the delays, delays in diagnosis and in treatment initiation were observed in 1,437 (28.8%) and 1,750 (39.2%) patients, respectively. On average, those patients had an 8.4 years gap between the first bleed and HA diagnosis and a delay of 8.6 years from the first bleed to treatment initiation. Additionally, 44.33% of patients relied solely on episodic treatments, and 16.2% received any prophylaxis treatments.

CONCLUSIONS

Using data from the largest haemophilia registry in China, this study indicated that delayed diagnosis and treatment, together with low utilization of prophylaxis, are key challenges for patients with HA.

Model of Short- and Long-Term Outcomes of Emicizumab Prophylaxis Treatment for Persons with Hemophilia A

BACKGROUND

Hemophilia A (HA) can result in bleeding events because of low or absent clotting factor VIII (FVIII). Prophylactic treatment for severe HA includes replacement FVIII infusions and emicizumab, a bispecific factor IXa- and factor X-directed antibody.

OBJECTIVE

To develop an economic model to predict the short- and long-term clinical and economic outcomes of prophylaxis with emicizumab versus short-acting recombinant FVIII among persons with HA in the United States.

METHODS

A Markov model was developed to compare clinical outcomes and costs of emicizumab versus FVIII prophylaxis among persons with severe HA from U.S. payer and societal perspectives. Patients started prophylaxis at age 1 year in the base case. Mutually exclusive health states considered were "no arthropathy," "arthropathy," "surgery," and "death." Serious adverse events, breakthrough bleeds, and inhibitor development were simulated throughout the modeled time horizon. In addition to the prophylaxis drug costs, patients could incur other direct costs related to breakthrough bleeds treatment, serious adverse events, development of inhibitors, arthropathy, and orthopedic surgery. Indirect costs associated with productivity loss (i.e., missed work or disabilities) were applied for adults. Model inputs were obtained from the HAVEN 3 trial, published literature, and expert opinion. The model used a lifetime horizon, and results for 1 year and 5 years were also reported. Deterministic sensitivity analyses and scenario analyses were conducted to assess robustness of the model.

RESULTS

Over a lifetime horizon, the cumulative number of all treated bleeds and joint bleeds avoided on emicizumab versus FVIII prophylaxis were 278.2 and 151.7, respectively. Correspondingly, arthropathy (mean age at onset: 12.9 vs. 5.4 years) and FVIII inhibitor development (mean age at development: 13.9 vs. 1.1 years) were delayed. Total direct and indirect costs were lower for emicizumab versus FVIII prophylaxis for all modeled time horizons ($97,159 vs. $331,610 at 1 year; $603,146 vs. $1,459,496 at 5 years; and $15,238,072 vs. $22,820,281 over a lifetime horizon). The sensitivity analyses indicated that clinical outcomes were sensitive to efficacy inputs, while economic outcomes were driven by the discount rate, dosing schedules, and treatments after inhibitor development. Results for moderate to severe patients were consistent with findings in the severe HA population.

CONCLUSIONS

The model suggests that emicizumab prophylaxis confers additional clinical benefits, resulting in a lower number of bleeding events and delayed onset of arthropathy and inhibitor development across all time assessment horizons. Compared with short-acting recombinant FVIII, emicizumab prophylaxis leads to superior patient outcomes and cost savings from U.S. payer and societal perspectives.

DISCLOSURES

Funding for this study was provided by Genentech. Raimundo and Patel are employees of Genentech and own stock or stock options. Zhou, Han, Ji, Fang, Zhong, and Betts are employees of Analysis Group, which received consultancy fees from Genentech for conducting this study. Mahajerin received consultancy fees from Genentech for work on this study. Portions of this research were presented as a poster at the 2018 American Society of Hematology Conference; December 1-4, 2018; San Diego, CA.