Objective
The objective of this project is to identify and optimize compounds that inhibit G6PC1. The initial identification of such compounds will be achieved using the latest computer technology available for this purpose. The subsequent optimization of such compounds involves two related components. First, we seek to identify highly potent compounds. This will involve taking a compound that only inhibits G6PC1 when it is used at high concentrations and making chemical modifications that improve the compound so that it now inhibits G6PC1 at low concentrations. This means that a lower amount of the compound will have to be ingested to achieve the desired effect, namely the inhibition of G6PC1 with a resulting reduction in liver glucose production. Highly potent compounds are more likely to selectively inhibit G6PC1 and not bind other proteins in the body, thereby reducing side effects. Second, with respect to other proteins that might bind a G6PC1 inhibitor, the leading candidates are G6PC2 and G6PC3, which share 50% and 36% amino acid identity with G6PC1. G6PC2 is only found in pancreatic islet beta cells so if we develop a combined G6PC1 and G6PC2 inhibitor it would not be a problem in that islet beta cells are largely absent in people with advanced T1D. In fact, inhibition of G6PC2 is predicted to also lower blood glucose levels so a joint G6PC1 and G6PC2 inhibitor might be a more desirable proposition for attracting future support from a large pharmaceutical company because such a dual inhibitor would also be beneficial for individuals with T2D. In contrast to G6PC2, we seek to identify compounds that inhibit G6PC1 but not G6PC3. Inhibition of G6PC3 has several negative consequences for human health. Given the low amino acid conservation between G6PC1 and G6PC3 we are confident that this can be achieved.
Background Rationale
In an individual without T1D the liver produces glucose during the night for consumption by other cells in the body, in particular brain cells. During the day the liver takes up glucose after a meal and stores it. The rates of glucose production and uptake by the liver are tightly controlled so these individuals maintain a low blood glucose level. However, in an individual with T1D the rate of liver glucose production is elevated both during the night and even after a meal. This increased glucose production contributes to the elevated glucose levels in individuals with T1D and ultimately promotes the development of diabetic complications.
This elevated liver glucose production in individuals with T1D is caused in part by the activity of an enzyme called G6PC1 being too high. Drugs that reduce the activity of G6PC1 would therefore limit this liver glucose production. We envisage that this drug would be taken at bedtime and would work during the night to reduce G6PC1 activity but it would also be taken during the day to promote glucose uptake by the liver after meals. Our emphasis is on developing drugs that reduce but do not completely block G6PC1 activity. This is critically important for the success of this approach because a complete block of G6PC1 activity would result in hypoglycemia. The pharmaceutical industry has shown that the development of such partial inhibitors can be accelerated if the structure of the target protein is known. Thanks to an incredible computer program developed by a company called DeepMind, which is owned by Google, we now have a structure for G6PC1. We can now use other computer programs that can assess the ability of different chemicals to bind this G6PC1 structure. We can then have these chemicals synthesized in a laboratory and test their ability to inhibit G6PC1 in a test tube. In the next stage of the project, we would then test the ability of promising drugs to reduce liver glucose production in animals. Ultimately, if the experiments in animals are successful, the goal is to test promising drugs in clinical trials. In summary, this project seeks to identify and then test compounds that bind and inhibit G6PC1 and thereby suppress liver glucose production.
Description of Project
Since starting my PhD studies at Cambridge University in 1984 my career has been spent studying aspects of diabetes related to insulin signaling and insulin secretion. More recently, in my role as the Research Information Volunteer (RIV) for the JDRF Nashville Chapter Board since 2019, I have learnt a lot about the latest research advances specifically supported by the JDRF. However, it’s the other Board members and the JDRF staff who have taught me the most about the practical challenges of living with type 1 diabetes (T1D) on a daily basis. Clearly the advent of continuous glucose monitoring systems has been a tremendous advance that has reduced the frequency of extreme glucose excursions for many individuals. However, a graph showing a comparison of average HbA1c versus the age of the individual with T1D striking reveals that, in most young people, HbA1c levels remain markedly elevated, which we know increases the risk for long term complications associated with this disease. In contrast, most individuals with T1D who are over age 30 are able to achieve low average HbA1c levels, though, in these older individuals, those HbA1c levels are still elevated relative to the levels in individuals without T1D. The reason for this difference between young and older individuals is hypothesized to arise due to the more settled lifestyle of older individuals. These data show that additional approaches are needed to control blood glucose levels, especially in young individuals with T1D. One promising approach is to develop therapies that slow the onset of diabetes in individuals with islet autoantibodies, the logic being that if diabetes can be delayed until an individual is age 30 or above they will be in a stage of life where they are better able to control their blood glucose level. Indeed, with considerable assistance from the JDRF, the first such therapy (Tzield/teplizumab) has just come to market. However, the delay in disease onset provided by such therapies currently appears to be limited. Therefore, alternate approaches are needed to control blood glucose levels. This application is focused on such an alternate therapeutic approach.
The strategy we are proposing to develop to regulate blood glucose levels is to develop inhibitors that reduce the activity of a protein called G6PC1. This protein is an enzyme that plays a key role in the production of glucose by the liver during fasting, in other words when an individual is asleep overnight. The liver normally produces this glucose during the night for consumption by other cells in the body, in particular brain cells. In an individual without T1D the rate of glucose production is tightly controlled so these individuals maintain a low blood glucose level. However, in an individual with T1D the rate of glucose production is elevated in part because G6PC1 activity is too high. Drugs that reduce the activity of G6PC1 would therefore limit this liver glucose production. This application requests funding for development of such drugs. The emphasis is on developing drugs that reduce but do not completely block G6PC1 activity. This is critically important for the success of this approach because a complete block of G6PC1 activity would result in hypoglycemia. A number of scientific breakthroughs over the past 2 years, both biochemical and computer based, have coalesced such that we are now in a position to develop partial G6PC1 inhibitors.
Anticipated Outcome
We anticipate that this project will lead to the identification of compounds that partially inhibit G6PC1. The emphasis will be on developing drugs that reduce but do not completely block G6PC1 activity. This is critically important for the success of this approach because a complete block of G6PC1 activity would result in hypoglycemia.
Relevance to T1D
This project is directly relevant to T1D and involves developing a new approach to regulate blood glucose levels. Specifically in this application we seek to take the first step in the development of drugs that reduce the activity of a protein called G6PC1. This protein is an enzyme that plays a key role in the production of glucose by the liver during fasting, in other words when an individual is asleep overnight. The liver produces this glucose during the night for consumption by other cells in the body, in particular brain cells. In an individual without T1D the rate of glucose production is tightly controlled so these individuals maintain a low blood glucose level. However, in an individual with T1D the rate of glucose production is elevated in part because G6PC1 activity is too high. Drugs that reduce the activity of G6PC1 would therefore limit this liver glucose production. We envisage that this drug would be taken at bedtime and would work during the night to reduce G6PC1 activity. However, we envisage that this drug would also help with the control of blood glucose levels during the day because in individuals with T1D the liver continues to produce glucose even during the day while these individuals are feeding. In a healthy person this liver glucose production is completely shut off during the day while feeding.
Importantly, the groundbreaking Diabetes Control and Complications clinical trial (DCCT), that was led by investigators at Vanderbilt University, established the precedent for the utility of regulating glucose levels during the night. The individuals assigned to the tight glucose control arm of the clinical trial would check their blood glucose during the night and inject insulin if needed. The reduction in diabetic complications in these individuals, relative to the standard therapy control group, was so profound that the clinical trial was ended prematurely so that everyone with T1D could benefit from this information. Clearly a drug that controlled glucose levels at night, while not requiring an individual to have to monitor their blood glucose level during the night, would be a huge benefit to those living with T1D. Studies have shown that disrupted sleep patterns are a major challenge facing individuals living with T1D. The advent of continuous glucose monitoring has not solved this problem and in some ways can make it worse if alarms on the device are frequently triggered during the night. Therefore, a drug that helped to suppress glucose production during the night in conjunction with continuous glucose monitoring would greatly benefit the T1D community.