From molecule to medicine - peptide and protein drugs30 September 2015
Peptide and protein drugs are becoming more popular but face significant hurdles in development. Natalie Healey meets Dr Lars Fogh Iversen, Novo Nordisk’s corporate vice-president, to discuss engineering tricks for turning an endogenous molecule into a viable drug product, and whether an oral version of insulin will ever make it to market.
In January 1922, 14-year-old Leonard Thompson became the first person to receive an injection of insulin as treatment for his type 1 diabetes. It wasn't a great success to start with; the Canadian experienced an allergic reaction initially. But after the process was refined, the second dose was successfully delivered. Thompson showed signs of improved health and went on to live for a further 13 years before succumbing to pneumonia at age 27.
Prior to the introduction of clinical insulin, diabetes was essentially a death sentence. But since the emergence of this endogenous therapy, patients have been able to live relatively normal lives.
Protein drugs (such as insulin, which is composed of 51 amino acids) have some advantages over their small-molecule counterparts, which might explain why they're proving popular for the pharmaceutical industry at the moment. In the 1970s, the average frequency of protein or peptide drugs entering clinical trials was around one a year, but by 2020, that number will be close to 20.
"I think the main advantage is that we're using nature's own template when we embark on making it into a drug molecule," explains Novo Nordisk's corporate vice-president Dr Lars Fogh Iversen. "We generally see that we can get really selective activation of target sites from proteins, whereas with small-molecule drugs, there's a risk they can bind in molecular cavities that you didn't design for."
This poor selectivity of small-molecule drugs can often lead to worrying side effects, whereas pharmaceuticals based on endogenous peptides would, in theory, affect just the receptor you're targeting, and there would be less risk of adverse reactions.
Iversen has been in his role for the past eight years and is an expert on protein engineering. His organisation's mission, since its inception in the early 1920s, has been to research and develop interventions for the prevention, treatment and cure of diabetes. Back then, two small Danish companies called Nordisk Insulinlaboratorium and Novo Terpeutisk Laboratorium produced the then-revolutionary insulin. After decades of intense competition, the two entities finally merged in 1989 to form Novo Nordisk, the global drug company we know today.
Aside from insulin, one of the major types of protein drugs that Novo Nordisk and other pharmaceutical companies have been researching is GLP-1 analogues. GLP-1 (or glucagon-like protein-1) is a metabolic hormone called an incretin. Once bound to the beta cells of the pancreas, the protein causes a decrease in blood sugar by increasing the amount of insulin released from the organ. It can be a useful treatment option for patients with type 2 diabetes when tablet therapies such as metformin have failed to alleviate their symptoms.
"That release of insulin is done in a glucose-dependent manner," explains Iversen. "That's the very elegant trick of GLP-1. When blood glucose is high, you get an insulin release, but when the glucose is back to normal, no more insulin is released. It regulates insulin so it matches the glucose levels, and that's extremely important when we are dealing with controlling diabetes."
Interestingly, GLP-1 analogues have also been shown to reduce appetite. Early preclinical studies revealed that animals given this type of drug lost weight. Clinical trials in humans also appear to support this. It means GLP-1 drugs might soon be regularly prescribed as obesity treatments.
However, as Iversen can testify, while endogenous proteins might make good starting points for drug discovery, developing something that works well, and ultimately creating a therapy a patient is actually willing to take, can be tricky.
"We're dealing with very delicate molecules," he says. "The overarching goal of a lot of protein engineering in the field is to improve the pharmacokinetics of proteins and peptides."
He says that natural GLP-1 has a half-life in humans of a few minutes. "It doesn't really render itself as being a drug molecule because you don't really get any good pharmacology out of a molecule that only circulates for a short time."
So the goal with GLP-1 has been to get a circulating half-life of the protein that makes it worth administrating in the first place. Iversen's team realised, through infusion studies, that 24-hour coverage of GLP-1 in the body would be required for an effective therapeutic effect. After using the group's protein engineering expertise, a once-daily version of the protein was produced; liraglutide (marketed under brand name Victoza) was approved for treatment of type 2 diabetes by the EMA in July 2009, and reached the US, approved by FDA, in January 2010. At the end of last year, FDA agreed to liraglutide being used to treat obesity in adults, with some related co-morbidity.
How, though, do you take a protein that is destroyed by the body in minutes, and turn it into a drug whose effects will last all day? Iversen explains that several technologies exist to help with this conundrum. Processes were sought out that would either extend the absorption phase of the peptide or prolong its half-life. Better yet, an option that combines the two to prevent its degradation would be ideal.
"What we try to do at Novo Nordisk is what we call lipidation of the peptide," he explains. "Here, we attach a fatty acid to the molecule's backbone. The fatty acid will then protect against degradation of GLP-1."
The lipidated peptide will bind more readily with serum albumin (the most prevalent protein in the blood), which will delay its excretion in the kidneys.
Novo Nordisk used the same process to develop semaglutide, a GLP-1 product that only needs to be injected once a week. The first phase-III trial of this drug was completed recently, when 388 people with type 2 diabetes were randomised to receive 0.5mg, 1.0mg or a placebo. Results showed that 74% of patients in the 0.5mg group and 73% of people in the 1.0mg group achieved blood glucose levels below 7%, compared with 25% of the placebo group. No major side effects were reported.
"To make semaglutide, we used the same basic technology as for liraglutide, but we played around with the fatty acids and made some alternations to make it bind stronger to albumin," says Iversen. "The stronger the binding to albumin, the longer the circulation half-life we can obtain. By trimming and designing the fatty acids, we can decide if our molecules will have a half-life of a few minutes to a week."
For diabetes pharmacology, the holy grail would be insulin that can be taken as a tablet, rather than as an injection. Oral delivery of the protein could significantly improve the quality of life for diabetics who routinely receive this treatment. It offers many advantages from higher patient compliance, to potentially avoiding hypoglycaemia and weight gain.
If protein molecules are taken orally, they would ordinarily be attacked by the digestive enzymes in our guts and broken down. This is useful for gaining energy from the food we eat but not so helpful for drug delivery. Insulin and GLP-1 in tablet form have to be designed to overcome this challenge, and later ensure absorption by the body in the right quantities to stay in the blood for the correct length of time, regardless of whether the patient has eaten much that day or not.
Oral insulin has, until recently, been considered a pipe dream, but Novo Nordisk has been working on making it a reality for a number of years. Its first candidate is currently in phase-I clinical trials.
Closer to being a success story is the oral form of semaglutide (or OG217SC), which recently impressed in its phase-II trial, where 600 people were treated for 26 weeks.
Mads Krogsgaard Thomsen, Novo's chief science officer, says the results of the recent semaglutide trials confirm the potential of the peptide as a once-weekly subcutaneous injection and as a once-daily tablet. He says: "This clinical proof of concept marks an important milestone for oral peptide therapy."
Iversen says that to create its oral semaglutide, Novo Nordisk required help from a contractor. Making a tablet form of a peptide drug is harder than simply extending the half-life of an injection formulation.
"We had to partner up because we were strong in protein engineering but not in oral delivery," he says. "We used our strong side and combined it with external technology to have a shot at gold on this."
The technology the organisation selected helps molecules get through the intestinal barrier, as with the use of SNAC (sodium N-[8-(2-hydroxybenzoyl) amino] caprylate), which is a small-molecule enhancer. The absorption-enhancing excipient acts as a carrier to facilitate transporting the poorly soluble therapeutic molecule across biological membranes and allows the drug to exert its pharmacological effect. So far, results have been promising.
But Iversen is cautious not to give any specific dates on when an oral peptide from Novo Nordisk might hit the market. However, he is excited about the idea of such drugs with more preferable delivery options emerging in the near future.
"Everyone across the industry is trying to make delivery of peptides and proteins as convenient as possible," he says. "I think new technologies will come to solve the problem, simply because there is so much pressure from patients saying we need to do this. I'm very optimistc about using proteins and peptides going forward."