Opportunities for using peptides and proteins as medicine are often limited by the fact that the digestive system breaks down the peptides and proteins and then the body cannot absorb very much. Danish researchers want to help to solve this problem.
Danish researchers want to solve the problem of delivering medicine with peptides or proteins through tablets.
Achieving this goal will open up a whole new market for medicine for everything from metabolic diseases to intestinal infections.
Although the researchers must untie a Gordian knot, they have already made their first breakthrough. They hope by the end of a major ongoing project to have developed a knowledge and technology platform that will revolutionize the opportunities that the pharmaceutical industry has to manufacture medicine.
“We are driven by a desire to use peptides and proteins more efficiently in manufacturing medicine. We also want to understand how peptides and proteins interact with the body,” says Hanne Mørck Nielsen, Professor, Center for Biopharmaceuticals and Biobarriers in Drug Delivery, Department of Pharmacy, University of Copenhagen.
The Novo Nordisk Foundation awarded a Challenge Programme grant to Hanne Mørck Nielsen and her colleagues so that they could get to the bottom of this problem.
Medicine with peptides and proteins has great potential
Most oral medicine comprises small molecules that are neither peptides nor proteins. The reason is that delivering medicine orally using peptides and proteins is difficult.
However, peptides and proteins are very promising pharmaceutically because they can replace or interact with the body’s own signalling pathways and thus can help the body to counteract, for example, metabolic diseases or inflammatory bowel diseases.
However, the overriding problem with ingesting peptides and proteins is that the body’s digestive system simply breaks the peptides or proteins into small pieces before they can have any effect.
First, the medicine is enveloped in gastric acid, and if this does not destroy the peptide or protein, the many enzymes produced by the digestive system do.
This was precisely the problem Novo Nordisk faced in developing their oral medicine made with peptides, specifically semaglutide. Administered in pure form orally, it would be degraded before it could have any effect.
“The body is geared to break down the peptides and proteins we ingest orally, and the great challenge for the pharmaceutical industry is how to deliver an active ingredient across the intestinal barrier if it has already been broken down long before it reaches the intestines,” asks Hanne Mørck Nielsen.
More than 90% of all peptide and protein medicine is administered by injection
This problem means that therapies based on proteins and peptides for many metabolic and inflammatory diseases are administered by injection. This is a daily inconvenience for many people with diabetes, for example.
Medicine for injection is also expensive for pharmaceutical companies to produce because this places high demands on sterility in manufacturing.
The potential to get medicine based on peptides and proteins into the bloodstream through oral delivery and across the intestinal barrier is therefore promising.
For example, protein-based medicine may be very relevant and promising for treating intestinal diseases such as ulcerative colitis or Crohn’s disease, for which the medicine should preferably be delivered to the site in the intestine where the inflammation occurs.
Medicine based on peptides can also often be promising for treating people with metabolic diseases because the peptides are often present in the signalling pathways that cause high blood pressure, obesity, high cholesterol, high blood glucose and the like.
“Today, at least 90% of all peptide and protein medicines are administered by injection, but this is not always desirable for many reasons,” says Hanne Mørck Nielsen.
Bridging several ways to approach the problem
The problem of delivering medicine based on peptides and proteins orally and to the intestine can be approached in various ways.
• Pharmaceutical companies can change the tablet or capsule so it dissolves very late, with the active ingredient cargo being released only when the medicine has arrived where it can be transported across the intestinal barrier. This may be part of the solution in some cases.
• Pharmaceutical companies can try to change the structure of the medicine so that the body’s digestive enzymes cannot so easily break it down while ensuring that the medicine retains its function. This solution may be appropriate in other cases but may not always be feasible.
• Pharmaceutical companies can adjust the contents of the tablet or capsule with functional excipients (vehicles for the active ingredient), such as cell-penetrating peptides, designed to deliver a larger fraction of the peptide active ingredient to and through the intestinal wall.
Hanne Mørck Nielsen’s research attempts to integrate these options by creating knowledge and solutions that can bridge them.
“Many things happen in the body from the time the medicine is ingested until it is absorbed through the stomach or intestinal wall, and we want to understand this whole biological and chemical process and be able to influence this process while maintaining user safety,” explains Hanne Mørck Nielsen.
The intestinal wall is designed to prevent the penetration of foreign matter
Some of the solutions on which Hanne Mørck Nielsen is working attempt to improve knowledge of what happens when an active ingredient needs to cross the intestinal wall.
The intestinal wall is a relatively impenetrable barrier of intestinal cells bound together by cell-binding proteins that hold the cells together like a zipper.
Overall, the layer of intestinal cells and cell-binding proteins means that hostile proteins and peptides cannot enter the bloodstream on the other side of the intestinal barrier. This is a natural defence against foreign bodies, but it also blocks potentially beneficial proteins and peptides.
In addition, the entire surface of the intestine is covered by a mucus layer through which the proteins and peptides must first pass before they can penetrate the intestinal cells.
“Developing new oral medicine based on peptides or proteins requires considerable manipulation to make them effective. For example, the tablet or capsule could have excipients that help the peptide or protein to penetrate the mucus layer and perhaps the intestinal barrier. In this context, we first have to understand how various excipients interact with the medicine, with the mucus layer and with the intestinal barrier. An active molecule group could also be attached to the peptide, such as a cell-penetrating peptide, so that the gut cells accept it more easily,” explains Hanne Mørck Nielsen.
Excipients protect proteins and peptides
Hanne Mørck Nilsen’s research also focuses on another type of excipient that shields the peptides and proteins as they pass through the gut.
Both peptides and proteins have sensitive sites in their structures where digestive enzymes can attack them and begin to break them down.
If excipients can shield these sensitive sites, the active ingredient may survive much longer in the gut. This strongly influences how much of the active ingredient is available to be absorbed and therefore be effective.
“But the active ingredients and the excipients cannot just be mixed and put into a tablet and then it works. The active ingredient and the excipients often interact to create the effect, and understanding this interaction is important. Further, active ingredients vary widely, so an excipient that influences one active ingredient may not work with another one. Transferring a concept from one form of medicine to another requires more detailed studies and more detailed understanding of the interactions between the excipients and the active ingredients,” says Hanne Mørck Nielsen.
Difficult approval process for new excipients
A separate problem with the excipients is that the relevant health authorities must thoroughly test and approve them before they can be used in new medicine.
This requires a whole series of trials involving animals and humans before an excipient can be approved for people.
Hanne Mørck Nielsen and her research group are therefore also focusing on approved excipients as well as new and more specific excipients that have been or are being developed.
“We collaborate closely with other research groups, each with its own area of expertise. One group has expertise in synthesizing peptides, so when we get a good idea for modifying a peptide or an existing excipient, they make it for us. Other groups in our collaboration have expertise in various detailed methods of analysis,” explains Hanne Mørck Nielsen.
Peptides from HIV as a model for transporting medicine into cells
The major research project is set to last for 6 years, but already 30 months into the process, the research group has experienced their first successes.
The starting-point for the project was a large European Union project with 23 partners that collaborated on understanding some specific carrier peptides that can help to carry oral peptides to the intestinal barrier and get them to penetrate the intestinal cells.
The carrier peptides are designed based on similar structures in peptides from HIV that have the precise structure that can penetrate cells.
Hanne Mørck Nielsen’s group has investigated these peptides in greater detail to understand how they function and how they interact with the intestinal cells.
“Our first trial has improved our understanding of how they interact with both the cells of the intestinal wall and with the active ingredients,” says Hanne Mørck Nielsen.
Several experiments show that the researchers are onto something
The experiments in Hanne Mørck Nielsen’s laboratory are designed in three stages.
• The researchers investigate the relevant excipients in a liquid.
• Then they examine them in cell culture.
• Finally, they study them in rats.
“So far, our experiments have complemented each other very well, so the results of one type of experiment confirm the results of the others,” says Hanne Mørck Nielsen.
The research team works specifically with small peptide hormones, including insulin, and in several cases, all experiments show that the excipients interact with the active ingredients and that this interaction influences how the active ingredient is absorbed into the cells.
Creating a knowledge platform in this field
Hanne Mørck Nielsen hopes that, when the project is completed in 3.5 years, she will have a knowledge platform that will inspire future efforts.
She aims to lay the foundations for understanding that can benefit both research and industry in the future.
“Of course, it would be nice if we end up with an excipient that can function with many peptides, but that is not the inherent goal. The goal is to obtain academic understanding of how to manipulate substances when designing oral medicine based on peptides or proteins. We would then also like to determine which techniques we need to carry out this manipulation. In addition, we would like to make our research a focal point that can attract more partners both in Denmark and internationally, so that this field continues to be cultivated and developed,” says Hanne Mørck Nielsen.
“Applications and challenges for use of cell-penetrating peptides as delivery vectors for peptide and protein cargos” has been published in the International Journal of Molecular Sciences. In 2016, the Novo Nordisk Foundation awarded a Challenge Programme grant to Hanne Mørck Nielsen for the Center for Biopharmaceuticals and Biobarriers in Drug Delivery.
