Minimizing Mitogenic Potency of Insulin Analogues Through Modification of a Disulfide Bond

Diboronate-Modified Hyaluronic Acid for Glucose-Responsive Insulin Delivery

Diabetes requires precise insulin management to maintain glycemic control and prevent severe complications. Glucose-responsive delivery systems envision an autonomous approach to improve insulin therapy. Here, a glucose-sensitive insulin delivery system comprising hyaluronic acid conjugated with a diboronate glucose binder as a carrier for diol-modified insulin is shown. This approach seeks improved precision in insulin delivery, leveraging bidentate glucose binding to achieve enhanced glucose affinity and specificity. Modification of insulin with a diol motif preserves its native conformation and function. These insulin formulations correct blood glucose in diabetic mice, including glucose-responsive function when subjected to a glucose challenge. However, the absence of secondary interactions, such as electrostatic complexation, ultimately limits the duration of function relative to that of previous platforms. Integrating complementary interactions alongside dynamic-covalent glucose binders therefore enhances the functional duration and therapeutic efficacy in the design of glucose-responsive polymeric carriers, offering design insights into the development of new carriers for glucose-responsive insulin delivery.

Insulin-Dendrimer Nanocomplex for Multi-Day Glucose-Responsive Therapy in Mice and Swine

The management of diabetes in a manner offering autonomous insulin therapy responsive to glucose-directed need, and moreover with a dosing schedule amenable to facile administration, remains an ongoing goal to improve the standard of care. While basal insulins with reduced dosing frequency, even once-weekly administration, are on the horizon, there is still no approved therapy that offers glucose-responsive insulin function. Herein, a nanoscale complex combining both electrostatic- and dynamic-covalent interactions between a synthetic dendrimer carrier and an insulin analogue modified with a high-affinity glucose-binding motif yields an injectable insulin depot affording both glucose-directed and long-lasting insulin availability. Following a single injection, it is even possible to control blood glucose for at least one week in diabetic swine subjected to daily oral glucose challenges. Measurements of serum insulin concentration in response to challenge show increases in insulin corresponding to elevated blood glucose levels, an uncommon finding even in preclinical work on glucose-responsive insulin. Accordingly, the subcutaneous nanocomplex that results from combining electrostatic- and dynamic-covalent interactions between a modified insulin and a synthetic dendrimer carrier affords a glucose-responsive insulin depot for week-long control following a single routine injection.

The three-dimensional structure of insulin and its receptor

Insulin is a peptide hormone essential for maintaining normal blood glucose levels. Individuals unable to secrete sufficient insulin or not able to respond properly to insulin develop diabetes. Since the discovery of insulin its structure and function has been intensively studied with the aim to develop effective diabetes treatments. The three-dimensional crystal structure of this 51 amino acid peptide paved the way for discoveries, outlined in this review, of determinants important for receptor binding and hormone stability that have been instrumental in development of insulin analogs used in the clinic today. Important for the future development of effective diabetes treatments will be a detailed understanding of the insulin receptor structure and function. Determination of the three-dimensional structure of the insulin receptor, a receptor tyrosine kinase, proved challenging but with the recent advent of high-resolution cryo-electron microscopy significant progress has been made. There are now >40 structures of the insulin:insulin receptor complex deposited in the Protein Data Bank. From these structures we have a detailed picture of how insulin binds and activates the receptor. Still lacking are details of the initial binding events and the exact sequence of structural changes within the receptor and insulin. In this review, the focus will be on the most recent structural studies of insulin:insulin receptor complexes and how they have contributed to the current understanding of insulin receptor activation and signaling outcome. Molecular mechanisms underlying insulin receptor signaling bias emerging from the latest structures are described.