Drug cab for insulin

Up to three percent of people with diabetes have an allergic reaction to insulin. A team at Forschungszentrum Jülich has now investigated a method that could be used to deliver the active ingredient into the body in a masked form – in the form of tiny nanoparticles. The insulin is only released in the target organ when the pH value deviates from the slightly alkaline environment in the blood. The molecular transport system could also serve as a platform to release other drugs in the body precisely at the target site.

Anastasiia Murmiliuk at the small-angle scattering diffractometer KWS-2 of the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching at the rheometer. The MLZ is home to the largest branch of the Jülich Center for Neutron Science. © Bernhard Ludewig, FRM II / TUM

Anastasiia Murmiliuk at the small-angle scattering diffractometer KWS-2 of the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching at the rheometer. The MLZ is home to the largest branch of the Jülich Center for Neutron Science. © Bernhard Ludewig, FRM II / TUM

It is an old dream in pharmacy: to deliver an active ingredient in the body exactly where it is most needed – a cancer drug, for example, directly into the tumor tissue. This minimizes its side effects on other organs and ensures that it has its maximum effect at its target. “Targeted drug delivery” is the name of this concept. The active ingredient is packaged in a transport substance and thus introduced into the body. Once at its destination, a specific stimulus (e.g., the oxygen content or pH value) ensures the encapsulated cargo is rereleased.
A team at Forschungszentrum Jülich has just presented the concept for such a drug cab, which could benefit people with diabetes in particular. “Some of those affected are allergic to insulin – the drug that they have to use every day to adjust their blood sugar levels,” explains Anastasiia Murmiliuk, a researcher at the Jülich Centre for Neutron Science (JCNS) who played a crucial role in the development and characterization of the molecular transport system.

An allergy to insulin is rare. But especially in people with type 1 diabetes, there is no alternative to administering the messenger substance. The skin around the injection site reddens each time the insulin preparation is injected. The area swells, itches, and hurts. It can even result in an anaphylactic reaction with shortness of breath and circulatory problems. “Our idea was to mask the insulin for the immune system. To do this, we selected a synthetic polymer that binds the insulin to itself,” says the chemist.
The complexes of insulin and polymer molecules combine to form nanoparticles, which can then be transported from the blood vessels to the organs. In the slightly alkaline environment of the blood, the two components initially remain firmly bound together. However, the pH value changes in the tissue – and insulin and polymer separate.

“Polymers, i.e., long-chain molecules, are fascinating compounds. Their properties can be tailored to specific applications,” says Anastasiia Murmiliuk. The polymer the researcher selected for insulin transport is biodegradable and consists of two units: a water-loving part, which ensures solubility and stability in the blood, and a charged part, which binds the insulin.

Using various scattering methods, the Jülich team determined not only the particles’ size but also their internal structure: The water-loving sections of the polymer form the outer shell of the particles. At the same time, the charged chain parts nestle against the insulin on the inside. “We were able to show that three insulin molecules lie close together,” explains Anastasiia Murmiliuk. In many conventional preparations, insulin is dissolved in a six-pack, which then has to gradually break down into the active individual molecules. The three-pack in the nanocarriers could, therefore, act more quickly.
The small-angle neutron scattering method has proven to be particularly useful for studying the polymer insulin particles, says Aurel Radulescu, neutron scattering expert at JCNS: “Unlike X-rays, neutrons can ‘see’ the hydrogen in a sample and distinguish between hydrogen and deuterium (heavy hydrogen). Suppose we replace the hydrogen in all but one component of the nanoparticles with deuterium. In that case, we can precisely visualize only this one component, i.e., only the polymer or only the insulin. In this way, we can selectively generate the contrast between the two components and the solvent and see in detail how our drug cab is constructed.

“It was essential to analyze a wide size range from a few angstroms to micrometers with the same neutron instrument to ensure a thorough structural analysis of the polymer-protein complexes and their larger assemblies. There are very few small-angle neutron diffractometers in the world that offer this capability, and we have included some in our study,” says Radulescu.

Aurel Radulescu and Anastasiia Murmiliuk in front of the SANS-J small-angle neutron diffractometer at the Japan Research Reactor 3 in Tokai, Japan. © Japan Atomic Energy Research Institute

Aurel Radulescu and Anastasiia Murmiliuk in front of the SANS-J small-angle neutron diffractometer at the Japan Research Reactor 3 in Tokai, Japan. © Japan Atomic Energy Research Institute

So far, the team has only been able to show in the laboratory that the molecular transporter works. Studies in blood and tissue samples are still pending. Nevertheless, the researchers believe that complexes consisting of a synthetic polymer and a natural protein such as insulin can be developed into a pharmaceutical platform. This would allow insulin and a wide range of active substances to be efficiently introduced into the body: “We tried this out with a dye that occurs in a similar form in blood or leaf green and is used to diagnose and treat cancer. It was trapped in the nanoparticles and was released after the pH value had changed significantly and the particles fell apart.”

In the future, this could also be used to encapsulate active ingredients that are poorly soluble in water. Radulescu and Murmiliuk are thinking primarily of cancer drugs. Since tumors have a different pH value than other cells, this approach can deliver cancer drugs directly to cancer cells without harming “healthy” cells.