Novo Nordisk researchers have solved a chemistry and biology riddle that has been pursued for nearly half a century: designing a glucose-sensitive insulin with auto-adjustable bioactivity. According to research published in Nature, the molecule, designed using computational chemistry and structural biology with reversible bioactivity, demonstrated responsiveness to a glucose range relevant to diabetes and led to protection against hypoglycemia in animal models while partially covering glycemic variability.
These results hold promise for improving the treatment of diabetes by potentially lowering the risk of hypoglycemia and partly covering the need for fast-acting insulin at mealtime, thus improving both the short-term and long-term risks and complications associated with diabetes. This method also lays the groundwork for showing that molecular switches can be created to enable autonomous control of molecular bioactivity in response to changes in another molecule’s concentration, even within a narrow range like blood glucose levels.
A short history of engineering insulin
Since the 1970s, efforts have been made to engineer an insulin that can adjust its bioactivity in response to fluctuating blood glucose levels, thereby enhancing glycemic control while mitigating the risk of hypoglycemia. Even though there have been many publications and patents on the subject, no mechanism has yet been shown to be compelling enough to treat diabetes. Most studies have focused on systems that can release insulin from subcutaneous depots in response to changes in glucose levels. Even so, these systems are limited by irreversibly, and insulin entering the bloodstream takes time to work.
An apparent more effective strategy is to give insulin glucose-responsive properties that let it respond to glucose reversibly. To achieve such an insulin molecule would require two key properties: glucose binding with optimal sensitivity to the fluctuating glucose levels in diabetics (from approximately 2 to 20–30 mM) and a mechanism to reversibly “shut off” insulin receptor binding activity at low glucose levels. To address glucose sensitivity, Merck created a system that changed insulin clearance and, consequently, insulin action in response to blood glucose. Still, because of its incredibly low efficacy, this system did not merit advancement past phase I clinical trials. The closest example of a reversely glucose-sensitive insulin was created by Thermalin and Indiana University School of Medicine. It was insensitive to glucose but sensitive to fructose at high concentrations.
NNC2215 responds to glucose and reduces hypoglycemia
The two characteristics of glucose sensitivity and reversibility served as the foundation for the development of the NNC2215 insulin variant by Novo Nordisk researchers. NNC2215 relies on macrocycles, which are cyclic molecules that resemble drugs and have a large molecular size and a large binding surface with the receptors. The ability of macrocycles to affect biological and physiochemical properties and their superior selectivity over their acyclic counterparts has sparked a growing interest in medicinal chemistry. The approval of contemporary pharmaceutical agents like Lorlatinib for treating non-small cell lung cancer (NSCLC) demonstrates the noteworthy clinical relevance of drug-like macrocycles.
The Novo Nordisk researchers took inspiration from recent work by Ziylo and University of Bristol researchers who created a macrocycle with a glucose-binding cavity that ensures a relevant affinity for glucose and selectivity over other carbohydrates and possibly interfering small molecules. By using this macrocycle to form an insulin conjugate, NNC2215 showed that when glucose was increased from 0 to 20 mM, its insulin receptor binding affinity increased by 12.5 times, and when it was increased from 3 to 20 mM, it increased by 3.2 times.
The Novo Nordisk team tested NNC2215 in three in vivo animal models. First, in a rather straightforward acute rat model, the glucose sensitivity in vivo was confirmed by administering l-glucose at a dose that triggered the insulin effect of NNC2215 without inducing endogenous insulin release. When l-glucose activated NNC2215, d-glucose lowered dose-dependently, and NNC2215 was concurrently dose-dependently cleared by l-glucose. Second, during a glucose challenge in insulinopenic streptozotocin (STZ)-diabetic rats, the Novo Nordisk researchers also noticed an activation of NNC2215, equivalent to 30% more human insulin. Finally, NNC2215’s glucose-sensitive insulin receptor binding and cellular effects showed a protective effect against hypoglycemia in vivo using a pig model that resembles acute diabetes.
In conclusion, insulin conjugates with characteristics like NNC2215 can potentially improve diabetes treatment by reducing the risk of hypoglycemia and partially substituting for the need for fast-acting insulin during meals. Compared to existing insulin therapies, combining these two characteristics should enable more aggressive insulin titration to reach normal glucose levels without raising the risk of hypoglycemia. This could reduce the risks and complications of diabetes in the short and long term.
