Research examines novel treatment techniques for hemophilia B, VTE

Bleeding and clotting disorders affect a large number of patients annually and, while accurate diagnosis is important, timely and effective treatment for these disorders is key, as they have the potential to quickly become life-threatening. Research examining novel treatment techniques for bleeding and clotting disorders will be presented today at the 53rd Annual Meeting of the American Society of Hematology.

Bleeding disorders, such as hemophilia B, are a group of conditions that result when the blood cannot clot properly. In normal clotting, platelets (cells that cause the blood to clot) stick together and form a plug at the site of an injured blood vessel, allowing the injured site to heal. Although the body naturally dissolves blood clots after an injury has completely healed, sometimes clots form on the inside of vessels without an obvious injury or do not dissolve naturally, leading to clotting disorders such as venous thromboembolism (VTE).

"In the United States alone, over half a million people a year develop inappropriate blood clots called thrombosis, and at least 100,000 people die each year from a pulmonary embolism.  Because these clots can be so deadly, and can occur unbeknownst to the patient, it is important that we find new ways to diagnose and treat them," said Charles Abrams, MD, moderator of the press conference, 2011 ASH Secretary, and Professor of Medicine at the University of Pennsylvania School of Medicine in Philadelphia. "While bleeding disorders, such as hemophilia, are less common than clotting disorders, they can still be extremely dangerous. Results of these studies provide hope for potential new treatments and demonstrate the next generation of gene therapy to correct defective genes."

This press conference will take place on Saturday, December 10, at 8:00 a.m. PST.

Aspirin After Oral Anticoagulants for Prevention of Recurrence in Patients with Unprovoked Venous Thromboembolism. The WARFASA Study [Abstract 543]

A new study shows that administering aspirin after standard therapy for venous thromboembolism (VTE) may prevent the recurrence of potentially deadly blood clots.

VTE is a clotting disorder that includes both deep-vein thrombosis and pulmonary embolism, which can lead to chest pain, rapid pulse, shortness of breath, and, in extreme cases, sudden death. Patients who suffer from VTE are given oral anticoagulants, such as warfarin, to help prevent clot growth and dissolve existing clots or emboli (detached clots) in the veins. Other antithrombotic treatments include antiplatelet agents, such as aspirin, which block the formation of blood clots in the arteries by preventing platelets from clumping together and obstructing the blood flow to the heart or brain, which can cause a heart attack or stroke.

Recurrence of these deadly clots develops in 15 to 20 percent of patients who suffer from VTE two years after they finish conventional warfarin treatment. Although extending anticoagulant treatment has been found to be effective in preventing recurrence, it is also associated with an increased bleeding risk. The use of aspirin as an alternative therapy to oral anticoagulants has been controversial because the drug is used to stop blood clots in the arteries and not veins. In addition, results of previous studies that have assessed its ability to reduce recurrence rates for VTE have been contradictory.

To assess the efficacy and safety of aspirin for the prevention of VTE recurrence after a conventional course of oral anticoagulation therapy, researchers from several Italian institutions embarked on the randomized, double-blind, placebo-controlled WARFASA study. The team sought to determine whether low-dose aspirin prevented recurrent symptomatic VTE when given for two years following an initial six to 12 months of warfarin therapy. Patients enrolled in the study with a first unprovoked VTE (clot that occurs in the absence of known risk factors, such as prolonged immobilization, surgery, or trauma), who had completed six to 12 months of oral anticoagulant treatment were randomized to receive a daily dose of aspirin (205 patients) or placebo (197 patients) for at least two years, with follow-up for up to 36 months. The primary efficacy outcome was objectively confirmed recurrent symptomatic VTE and VTE-related death. Clinically relevant (major and non-major) bleeding were the main safety outcomes.

VTE recurrence was observed in 28 of the 205 patients who received aspirin and 43 of the 197 patients who received placebo (6.6% vs. 11.2% per patient-year, respectively). While on study treatment, 23 patients who received aspirin and 39 patients who received placebo experienced VTE recurrence (5.9% vs. 11.0 % per patient-year, respectively). Major bleeding occurred in one patient in each treatment group, with a similar incidence of clinically relevant non-major bleeding.

"There has been significant debate on whether giving aspirin to a patient who suffers from VTE is beneficial," said lead study author Cecilia Becattini, MD, Assistant Professor of Internal Medicine in the Internal and Cardiovascular Medicine and Stroke Unit at the University of Perugia in Italy. "Our study shows that aspirin, a common and low-cost drug found in most medicine cabinets, can be a valid alternative to oral anticoagulants for the extended treatment of VTE."

Dr. Becattini will present this study in an oral presentation on Monday, December 12, at 3:15 p.m. PST at the San Diego Marriott Marquis & Marina in Hall 4.

Platelet Production System Using an Immortalized Megakaryocyte Cell Line Derived From Human Pluripotent Stem Cells [Abstract 2]

Researchers are one step closer to developing functional human platelets from induced pluripotent stem (iPS) cells that can be used in humans after creating them in vitro and proving their functionality in a mouse model.

"There is a chronic shortage of donated platelets in blood banks, because unlike other parts of the blood, platelets cannot be frozen and stored for an extended period of time," said Sou Nakamura, lead author of the study and Research Associate at the Center for iPS Cell Research and Application (CiRA) at Kyoto University in Japan. Human iPS cells are a promising source of blood cells, including platelets; however, the main limitation until now has been the ability to find a method that creates a large number of high-quality, functional platelets.

To address these limitations, investigators from CiRA and the Center for Stem Cell Biology and Regenerative Medicine at the University of Tokyo set out to create an immortalized cell line with a large number of high-quality megakaryocytes (precursor cells that develop into platelets) from human embryonic stem cells or iPS cells that can be grown indefinitely and differentiate into a variety of cell types in the body. Immortalized cell lines offer the possibility of a renewable supply of cells that can be used as models of animal or human tissue.

Previously, the research team had demonstrated that peak activation of c-MYC (a gene that is essential for the proliferation of human cells) in megakaryocyte progenitor cells, followed by a reduction of c-MYC expression, are key components of in vitro platelet generation. The team also found that the overexpression of c-MYC not only increased the number of megakaryocytes, but also induced apoptosis (cell death) and cell senescence (when cells can no longer divide and reproduce).

In this study, investigators created an immortalized megakaryocyte cell line by overexpressing c-MYC and the BMI1 gene (a polycomb gene essential for the prevention of senescence), which then generated functional platelets in vivo once the overexpression of those genes was turned off. The researchers further tested the functionality of the cultured platelets by infusing them into immunodeficient mouse models and confirmed that they had the same life span as normal human platelets infused in mice. 

"This is an exciting development for the transfusion community, as our methodology has proven that platelets can be created in the lab from human iPS cells," said senior author Koji Eto, MD, PhD, Professor at CiRA. "The next step will be to conduct a trial to determine whether our platelets can function in the human body and potentially provide a stable supply of platelets at a predefined quality and quantity that can then be used for transfusion therapy."

Naoya Takayama, MD, PhD, will present this study during the Plenary Scientific Session on Sunday, December 11, at 2:25 p.m. PST at the San Diego Convention Center in Hall AB.

Adeno-Associated Viral Vector Mediated Gene Transfer for Hemophilia B [Abstract 5]

Researchers have successfully tested a potential cure for severe hemophilia B in six patients using gene therapy.

Hemophilia B is a genetic bleeding disorder caused by defective or missing recombinant factor IX (FIX). Insufficient amounts of this protein prevents blood from clotting normally and can result in prolonged bleeding after injury or surgery, or spontaneous bleeding in the absence of trauma. This bleeding can cause permanent damage to joints, muscles, and other parts of the body, including the brain.

"While all patients who suffer from hemophilia B usually need replacement therapy, or infusion of recombinant FIX protein to replace the defective clotting factor after an episode of trauma, patients with a severe form of the disorder usually have to undergo frequent infusions, usually twice a week, to prevent spontaneous bleeding episodes," said senior author Andrew M. Davidoff, MD, Chairman of the Department of Surgery at St. Jude Children's Research Hospital in Memphis, Tenn. "Our ongoing research has been examining the use of gene therapy as a treatment approach for hemophilia B to relieve the burden of frequent infusions on these patients."

The strategy uses a gene transfer approach, which replaces the defective gene that causes the disorder with a correct version in the patient's liver cells, the normal site of FIX synthesis, so that patients can make their own FIX. Work on the vector was initiated at St. Jude more than a decade ago by Dr. Davidoff and Amit Nathwani, MD, PhD, co-lead study author, of the Department of Hematology at UCL Cancer Institute in London, United Kingdom, under the stewardship of Arthur W. Nienhuis, MD, also a co-author of the study and a member of the St. Jude Hematology department. Since the work was initiated, several other scientists and academic institutions have contributed to the complex international research effort.

A presentation during the 2010 ASH Meeting revealed preliminary results of the study, which evaluated two dose levels of a viral vector that enabled the transfer of a normal gene for FIX sufficient to generate therapeutic levels of the protein without causing adverse effects in four patients. Since then, investigators have administered the vector in two additional patients with severe hemophilia B at a higher dose and have now followed the entire cohort six to 16 months post treatment.

The six trial participants were given an infusion that contained a vector carrying a normal copy of the FIX gene via a vein in the arm. Two subjects were treated with a low dose, two with an intermediate dose, and two with a high dose of the vector. Vector-mediated levels of FIX rose from less than 1 percent of normal before therapy to between 2 percent and 12 percent of normal levels in all six patients. The FIX levels, in the first subject who has been followed for the longest time, have remained at 2 percent for more than 12 months following gene transfer. The highest level of FIX expression has been observed in the two subjects treated at the highest dose level, with expression ranging from 3 percent to 12 percent. Four of the six participants have discontinued prophylactic treatment and remain free of spontaneous bleeding, and the remaining two patients have increased the time interval between FIX infusions.

"We have developed a vector for gene transfer that is more efficient and effective than traditional treatment for patients with severe hemophilia B by preventing spontaneous bleeding in this high-risk patient population," said Dr. Nathwani. "Our novel approach shows promise for improved gene therapy of hemophilia B and other protein deficiencies."

Dr. Nathwani will present this study during the Plenary Scientific Session on Sunday, December 11, at 3:25 p.m. PST at the San Diego Convention Center in Hall AB.

Improved Functional Outcome After Additional Catheter-Directed Thrombolysis for Acute Iliofemoral Deep Vein Thrombosis: Results of a Randomized Controlled Clinical Trial (The CaVenT Study) [LBA-1]

In the largest randomized study performed to date, researchers have found that additional treatment with catheter-directed thrombolysis (CDT), when compared to standard treatment of oral anticoagulation therapy and elastic compression stockings (ECS), reduces the risk of post-thrombotic syndrome (PTS) in patients who suffer from deep-vein thrombosis (DVT) in their lower limbs.

PTS, a chronic complication of DVT that causes swelling, pain, cramping, and venous ulcers, occurs in approximately one in four patients who suffer from lower-limb DVT treated with standard therapy.

To reduce the risk of developing PTS, additional therapy is needed via catheter-directed thrombolysis (CDT), a minimally invasive procedure that uses x-ray imaging to administer medication to help dissolve clots through a catheter placed in the vein. CDT has become standard of care for the prevention of PTS in some treatment centers, despite a lack of randomized, controlled trials demonstrating its efficacy and safety, as well as several drawbacks including its high expense, association with life-threatening bleeding, and tendency to convert DVT (typically an outpatient condition) to an in-patient disease requiring hospitalization.

To evaluate whether additional treatment of DVT with CDT with alteplase (a clot-dissolving medication) reduces PTS development following acute iliofemoral DVT (occurring in the upper thigh and/or pelvic area), researchers embarked on the Catheter-Directed Venous Thrombolysis in Acute Iliofemoral Vein Thrombosis (CaVenT) study, a large, four-year, multicenter, randomized controlled trial.

In this trial, 209 patients between the ages of 18 and 75 with a first-time acute iliofemoral DVT, with symptoms present for up to 21 days, were randomized into two treatment arms: Treatment arm A (the CDT-treated arm) had 101 patients and arm B (control arm treated with oral anticoagulant and ECS) had 108 patients. The primary endpoint of the trial was the frequency of PTS after 24 months of follow-up.

Of the 90 CDT-treated patients and 99 control patients who had data available for analysis, 41.1 percent of patients treated with CDT presented symptoms of PTS compared to 55.6 percent of control patients. The difference in PTS incidence corresponds to an absolute risk reduction of 14.4 percent in patients treated with CDT.

Twenty bleeding complications were reported, three classified as major and five considered clinically relevant. None of the reported bleeding episodes caused serious complications, and there were no pulmonary emboli, strokes, or deaths related to treatment with CDT. After six months of follow-up, PTS developed in 36.9 percent of patients who no longer had a clotted vein, as compared to 61.3 percent of patients who still experienced clotting. These outcomes underscore the importance of recanalization, the unblocking of a blood vessel, for preventing PTS and ensuring positive outcomes in patients with DVT.

"The results of our trial show that additional treatment with CDT significantly reduces the risk of PTS in patients with DVT, compared to standard treatment alone," said Per Morten Sandset, MD, PhD, senior author and Head of Research, Clinic of Cancer, Surgery, and Transplantation at Oslo University Hospital in Norway. "Although CDT is a promising treatment option for patients with iliofemoral DVT, the therapy also increases the risk of bleeding, emphasizing the importance of patient selection and safety when performing CDT procedures. Our findings suggest that CDT should be considered in patients with upper thigh or pelvic DVT."

Dr. Tone Ronnaug Enden will present this study during the Late-Breaking Abstracts Session on Tuesday, December 13, at 7:30a.m. PST at the San Diego Convention Center in Hall AB.


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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