Objective
The objective of this proposal is to overcome the measurement challenges that are impeding the deployment of a continuous insulin monitor. The proposed solution leverages expertise in electrochemical, aptamer-based sensors (White), aptamer selection (Hollenstein) , endocrinology (Falciglia), and device development (Heikenfeld, Kilele Health) to develop continuous insulin monitors with the requisite specificity, selectivity, sensitivity, and longevity for insulin monitoring. Aptamers are short nucleic acid sequences (DNA or RNA) that when placed onto an electrode can target and capture and electrically measure a single molecule type even in a whole biofluid such as blood. The proposed work further takes a unique and smart approach of building an aptamer-based insulin sensor onto an existing continuous glucose monitor with mainly only chemistry modification of the sensor electrode, an approach that will expedite safe and affordable placement of insulin sensing with patients. Combined with the commercial expertise afforded by several corporate partners in the diagnostics industry, the end goal of this two-year project is the development of a prototype sensor device that will be adapted onto an existing continuous glucose monitor (e.g. Dexcom G7, Abbott Libre 3) but with sensitive detection of insulin. To achieve this goal, three aims are proposed:
Aim 1. Selection of Insulin-Binding Aptamer via Chemically-Substituted Bases with 10 pM Binding Affinities. Chemical modifications to aptamers will increase the sensitivity of the aptamers for measuring insulin.
Aim 2. Adapt the aptamers for Insulin Into an Electrochemical Sensor with >1 Week Longevity.
Aim 3. Demonstrate In Vivo, Calibration-Free Detection of Insulin with at least +/-20% error.
Background Rationale
The proposed research will lay the foundation for personalized, continuous insulin monitoring (CIM) for improved diabetes management and improved quality of life for those living with the disease. The resulting sensing technology is compatible with existing continuous glucose monitors relying on the same analytical measurement and is thus well poised to make immediate impact. Current mitigation strategies rely on insulin dosage to control glucose levels, however this strategy does not take into account insulin sensitivity or resistance and thus raises the risk of hypo- and hyperglycemia. The ability to quantify the dynamics of the glucose-insulin control network with coupled glucose and insulin monitoring will enable the ability to achieve tighter glycemic control. The need for insulin monitoring will continue to grow due to the immediate need for continuous glucose monitoring (CGM) and insulin administration for type 1 diabetes and then expanded use in type 2. The successful completion of the proposed research will provide a sensor capable of measuring in the minutes time scales insulin levels, limited only by physiological lag times of insulin exchange into the human dermis. The more complete picture of blood sugar and insulin levels will be a significant advance in personalized diabetes management and treatment. The parallelized measure of glycose and insulin is paramount to maximizing outcomes with artificial pancreases by accounting for diet, exercise, and everyday activities. Moreover, the ability to monitor insulin may help in the early identification of diabetes as well as the “carbohydrate-insulin” hypothesis argues that hypersecretion of insulin supersedes insulin resistance. Finally, the sensor will make immediate and significant impact in the basic research lab where insulin secretion measurements are performed routinely, but require expensive, time consuming, and cumbersome ELISA methods that lack temporal resolution.
Description of Project
Insulin is a peptide hormone, synthesized by the pancreas, to regulate the carbohydrate and fat metabolism to maintain glucose levels in the blood. Normal blood insulin levels are between 50 to70 picomolar insulin levels, and less than 50 picomolar or higher than 70 picomolar denote to Type I, or Type II Diabetes, respectively. Statistically, Diabetes will affect 422 million people around the world in 2030 and in order to be diagnosed and controlled properly, there is need to highly sensitive and effective methods for insulin analysis. Detection of insulin levels in the blood plays a crucial role in diagnosis of diabetes in the early stages since the accurate diagnosis requires the monitoring of both Insulin and glucose levels. Additionally, simultaneous detection of insulin and glucose provides better estimates for insulin sensitivity to precisely control the therapeutic insulin dose for diabetic patients. However, insulin detection has been more challenging, compared to glucose detection, due to its large molecular size, its picomolar concentration in the blood, and the presence of endogenous interfering species such as ascorbic acid, uric acid, and C-peptide. For these reasons, there is a necessity to develop highly sensitive and selective sensors for insulin analysis in the blood. Analytical techniques used in labs have been well-established to detect insulin but they suffer from high operational costs, expensive and bulky instruments, and long detection times. To enable a low cost wearable device like a continuous glucose monitor, an alternate approach is required, and outside of enzyme sensors like those used for glucose monitoring the most widely-demonstrated sensor platform in animal testing has been aptamers. This work proposes to enable wearable insulin monitoring on humans using the promising platform of aptamer sensors. Aptamers are short nucleic acid sequences (DNA or RNA), selected for targeting a molecule like insulin through a process called SELEX (systematic evolution of ligands by exponential enrichment. The selected aptamers can then be placed on a tiny wire electrode that is inserted into the body, much like glucose enzymes for glucose monitors, where the aptamers can bind to the target molecule to be measured and when they bind results in a measurable change in electrical current. Proposed here is a research program to develop an aptamer sensor into the first ever continuous insulin sensor. The proposed work leverages multiple recent breakthrough by the proposing researchers including: (1) a first generation insulin aptamer sensor that shows general proof of concept but which is not sensitive enough for human use; (2) the first ever demonstration of aptamer sensors that can operate for the important practical threshold of a week or more; (3) the ability to add aptamers to an existing continuous glucose meter such that the user needs only wear a single device that measures both glucose and insulin; (4) and the ability to chemically modify aptamers such that they can become ultrasensitive and therefore measure insulin at the challenging picomolar concentrations that exist in the body. The team proposes to accomplish these goals through step-wise research progress spanning fundamental aptamer selection and design, to sensor optimization, to a first compelling proof point of continuous insulin monitoring in a rodent model.
Anticipated Outcome
The anticipated outcome of this proposed work on creating a continuous insulin monitor is the initial feasibility that such a monitor can work accurately in the body at the levels of insulin required for diabetes and insulin control. While this initial data will be in rodents and for limited duration, the intial data enabled by JDRF represents a major breakthrough and sets up a series of additional commercially funded outcomes which include (1) full adaptation onto at least one commercial CGM device and 7-day ambulatory pig testing; (2) adaptation (if needed) into an at-home finger prick test-strip for calibration purposes like used for continuous glucose monitors; (3) Pre-FDA clinical testing at with normal health patients and then with diabetes patients. (4) A pre-submission meeting with the FDA to chart the path for further development and approval of a continuous insulin monitor for diabetes patients. (5) Eventually integration with closed-loop wearable insulin delivery systems for unprecedented levels of glycemic control in diabetes patients, creating essentially an ‘artificial pancreas’ to extend and improve the quality of lives for patients with diabetes.
Relevance to T1D
The pancreas produces very little or no insulin at all in people with type 1 diabetes. For this reason, everyone with type 1 diabetes will require insulin. Insulin is given under the skin, either as a shot or continuously with an insulin pump. By enabling continuous wearable monitoring of both glucose and insulin, type 1 diabetics are brough one step closer to having an artificial pancreas to control blood sugar levels like normal healthy individuals. Measuring insulin has been notoriously difficult for researchers and scientists to figure out, and this program by JDRF will enable key breakthroughs that for the first time ever point to real feasibility of making continuous insulin monitoring a reality for the patients that need it.