Insulin and glucagon play central roles in metabolic homeostasis with long-standing application to the clinical management of diabetes mellitus (DM). This MPI application focuses on the development of glucose-responsive analogs of these hormones. The proposed technology promises to enhance the safety and efficacy of hormone replacement therapy, including in innovative bihormonal pumps in closed-loop systems. This is a key frontier of molecular pharmacology and non-standard protein engineering. The multidisciplinary MPI team encompasses protein design, biophysics, structural biology, animal physiology, clinical endocrinology, and computer simulations of mammalian metabolism. Animal studies will be performed in normal and STZ rats under the guidance of Prof. F. Ismail-Beigi (Subcontract to CWRU); computer-based interpretation of these studies as part of a design cycle will be undertaken in simulated models by Prof. M. Strano and coworkers (Subcontract to MIT). Cryo-EM studies of variant insulin-insulin receptor (IR) complexes will be performed by Prof. M.C. Lawrence (Subcontract to WEHI, Melbourne AU). The MPI team has recent joint publications, including in Nature Chemistry, J. Biol. Chem. and Diabetes. Glucose-responsive insulin (GRI) analogs are envisioned as a technology to attenuate IR signaling under conditions of hypoglycemia; glucose-responsive glucagon (GRG) analogs are envisioned as a complementary technology to attenuate glucagon-receptor (GlR) signaling under conditions of hyperglycemia. Respective protein design rests upon two complementary premises: Hypothesis 1: That development of an appropriate glucose-binding element (GBE) will enable construction of a glucose-regulated conformational switch between a glucose-free closed (inactive) state and a glucose-bound open (active) state in accord with how WT insulin binds to and activates the IR; and Hypothesis 2: That development of a distinct GBE will enable construction of a glucose-regulated conformational switch between a glucose-bound inactive state and a glucose-free active state in accordance with how WT glucagon binds to and activates the GlR. In each case the GBEs will exploit the diol-binding properties boronic acids and benzoxaboroles. Binding of glucose in a GRI activates the hormone whereas binding of glucose in a GRG inactivates the hormone.
Aims 1 - 3 focus on GRIs whereas Aim 4 extends our approach to GRGs. These technologies may markedly enhance the long-term health of patients with T1D and a subset of patients with T2D. Protein design will be based on classical crystal structures of insulin and glucagon, extended by dramatic recent advances in the structural biology of the IR, GlR and their respective ligand complexes. Salient structural differences between these systems promise to enable construction of opposing switches. An interdisciplinary team Approach is proposed within integrated MPI Management Plan.
Non-standard analogs of insulin and glucagon will be designed to contain glucose-responsive elements such that each is regulated by the concentration of glucose in the blood stream. A glucose-responsive insulin (GRI) would be less active under conditions of hypoglycemia whereas a glucose-responsive glucagon (GRG) would be less active under conditions of hperglycemia. We envision that GRIs and GRGs will enhance the safety and efficacy of hormone replacement therapy in diabetes mellitus with particular application to bihormonal pumps in closed-loop systems.
