Stabilization of Glucagon by Trehalose Gylcopolymer Nanogels

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Project Summary Glucagon interacts with receptors in the liver to raise glucose levels. Normally glucagon is released endogenously. Yet for some diseases such as Type I diabetes, hypoglycemia defined as blood glucose level below 70 mg/dL occurs in a large number of patients. Hypoglycemia has side effects ranging from dizziness and shakiness, to blurry vision and seizures, to coma and death. To treat this potentially fatal condition, glucagon is administered via injection. However, glucagon is typically inactivated in solution within hours, forming amyloid- like fibers that are toxic and potentially dangerous for patients. This necessitates a complicated injection system wherein the peptide is kept as a dry powder and dissolved in acidic pH right before use. The acidity of the formulation causes pain at the injection site. A recently approved formulation circumvents this issue, but instead utilizes organic solvent, which is undesirable. Recently the PI discovered bioresponsive nanogels that stabilize glucagon in neutral solution for at least three weeks and maintain glucagon bioactivity. Nanogels containing a sugar stabilizer found in Nature, trehalose, were synthesized utilizing glucagon as the cross-linker. Under mildly reductive conditions the glucagon was released. Released glucagon and the glucagon nanoparticles were bioactive. This work is important because it suggests that trehalose nanogels can be utilized to stabilize glucagon in neutral solution and release active peptide when needed. Herein, it is proposed to build upon this foundation to prepare a new formulation for the stabilization and delivery of glucagon. Specifically, it is hypothesized that trehalose nanogels will stabilize glucagon in aqueous solutions and at room temperature, will release active glucagon and be safe and non-immunogenic in vivo. To test this hypothesis and meet the objectives, three specific aims are proposed. The first is to develop uniform sized nanogels and evaluate the long term stability of glucagon in the nanoparticle formulation. The achieve this, poly(methacrylate trehalose-co-pyridyl disulfide methacrylate) will be synthesized and cross-linked with bisthiolated poly(ethylene glycol). Glucagon will be loaded by covalent and physical encapsulation to form uniform gels. The resulting glucagon nanogels will be characterized and studied for long term solution and solid phase stability. Standard tests to observe aggregation of the glucagon and nanoparticles and chemical changes of the glucagon will be undertaken. Second will be to investigate in vitro and in vivo efficacy and bioavailability of glucagon nanogels. Standard cellular assays will be utilized to determine activity. Then an in situ liver perfusion assay will assess perfusate glucose concentrations upon exposure to the nanogels and allow for molecular signaling validation. Glucose counterregulation during insulin tolerance test will validate activity in whole animals. The third aim will be to determine in vivo safety of the nanoparticle formulation. Specifically, acute toxicity, biodistribution, excretion, pharmacokinetics, antibody generation and cytokine response to the nanogels will be tested in mice. This work is aligned with the long-term goal to provide new therapeutic tools to safely and effectively manage glucose levels for Type I diabetes patients.