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'Stealth' Particle Containing Factor VIII Could Prevent or Render Benign Inhibitor Antibodies in Hemophiliacs

Release Date: June 3, 2003

BUFFALO, N.Y. -- A tiny lipid particle developed by pharmaceutical scientists at the University at Buffalo School of Pharmacy and Pharmaceutical Sciences has the potential to improve significantly the lives of hemophiliacs who have developed a dangerous immune response to the frequent injections of factor VIII, the clotting factor that keeps them alive.

These lipid spheres contain significantly less water than conventional lipid particles, called liposomes, increasing their stability and allowing them to circulate in the body longer. This characteristic has potential advantages for other drug delivery applications as well.

According to Sathyamangalam V. Balasubramanian, Ph.D., UB assistant professor of pharmaceutical sciences, who is principal investigator, the lipid spheres act as "stealth" particles, sneaking past the body's immune system the factor VIII protein that hemophiliacs cannot adequately produce on their own without triggering a dangerous rejection.

Believed to be the only formulation in which lipid particles are being used to tackle factor VIII immunogenicity, this lipid-protein complex also would need to be administered less frequently, which could lower the cost of treatment for hemophiliac patients.

A provisional patent has been filed on the methods for producing these lipid-protein particles, which have been produced in the nanometer (billionth of a meter) range.

The UB researchers have tested the particles in normal rats and are beginning tests in a hemophiliac mouse model.

It is estimated that from 15-30 percent of all hemophiliacs develop inhibitors, antibodies that cause the body to recognize and destroy therapeutic factor VIII as a foreign substance. To overcome inhibitor development, patients either must switch formulations or undergo intensive therapy with factor VIII that can cost more $500,000 per year.

"We believe that our stable formulation will lead to the development of fewer inhibitors or none at all," said Balasubramanian, also a research assistant professor of biophysical sciences in the UB School of Medicine and Biomedical Sciences.

"The findings suggest that these factor VIII complexes not only would help to reduce or possibly avoid inhibitor development in patients who previously had not received treatment. They also may allow for clotting activity to resume even in treated patients who already have developed inhibitors," he said.

Balasubramanian took what he calls a "mechanistic" approach to the problem, designing the new formulation based on detailed bioinformatics and protein-folding studies that he conducted with factor VIII.

"With this novel formulation, we are hitting three birds with one stone, overcoming three disadvantages of current formulations," he added. The disadvantages are:

* In vivo instability and rapid clearance, necessitating frequent administration of the protein, which over time can trigger an immune response

* Formation of aggregates, where two or three factor VIII protein molecules clump together, rendering factor VIII protein inactive and sometimes contributing to a more pronounced immune response

* Exposure of a specific region on the protein -- the epitope region -- that is responsible for causing inhibitors to develop.

"From our structural studies of this extraordinarily large protein, we were fortunate to find that the amino acid region that triggers inhibitor development and aggregation also is the region of the protein that binds to lipids," Balasubramanian explained. "When the lipid binds to it, that epitope region is shielded from recognition by the body, significantly decreasing immunogenicity, and thwarting the formation of aggregates, allowing the protein to remain active."

And since the protein-lipid complex has the potential to circulate in the blood for longer than does free factor VIII, the drug can be administered less frequently, reducing the likelihood of an immune response, and potentially lowering the cost of treatment.

This research was funded by the National Institutes of Health.

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