Native Design of Soluble, Aggregation-Resistant Bioactive Peptides: Chemical Evolution of Human Glucagon

Investigation of Isobactin Analogues of Teixobactin

Although teixobactin is a promising antibiotic drug candidate against Gram-positive bacteria, it aggregates to form gels that may limit intravenous administration. We previously reported O-acyl isopeptide prodrugs of teixobactin analogues that address the problem of gel formation while retaining antibiotic activity. We termed these compounds isobactins. In the current Letter, we present nine new isobactin analogues that exhibit a reduced propensity to form gels in aqueous conditions while maintaining potent antibiotic activity against MRSA, VRE, and other Gram-positive bacteria. These isobactin analogues contain commercially available amino acid residues at position 10, replacing the synthetically challenging l-allo-enduracididine residue that is present in teixobactin. The isobactins undergo clean conversion to their corresponding teixobactin analogues at physiological pH and exhibit little to no hemolytic activity or cytotoxicity. Because isobactin analogues exhibit enhanced solubility, delayed gel formation, and are more synthetically accessible, it is anticipated that isobactin prodrug analogues may be superior drug candidates to teixobactin.

Isobactins: O-acyl isopeptide prodrugs of teixobactin and teixobactin derivatives

O-Acyl isopeptide prodrug analogues of the antibiotic teixobactin are stable and non-gelating at acidic pH but convert to the corresponding active teixobactin analogues at neutral pH, thus overcoming limitations in intravenous dosing of teixobactin.

Structurally Based Design of Glucagon Mutants That Inhibit Fibril Formation

The peptide hormone glucagon is prescribed as a pharmaceutical compound to treat diabetic hypoglycemia. However, at the acidic pH where it is highly soluble, glucagon rapidly aggregates into inactive and cytotoxic amyloid fibrils. The recently determined high-resolution structure of these fibrils revealed various stabilizing molecular interactions. On the basis of this structure, we have now designed four arginine mutants of glucagon that resist fibrillization at pharmaceutical concentrations for weeks. An S2R, T29R double mutant and a T29R single mutant remove a hydrogen-bonding interaction in the wild-type fibril, whereas a Y13R, A19R double mutant and a Y13R mutant remove a cation-π interaction. 1H solution nuclear magnetic resonance spectra and ultraviolet absorbance data indicate that these mutants remain soluble in pH 2 buffer under quiescent conditions at concentrations of ≤4 mg/mL for weeks. Under stressed conditions with high salt concentrations and agitation, these mutants fibrillize significantly more slowly than the wild type. The S2R, T29R mutant and the T29R mutant exhibit a mixture of random coil and α-helical conformations, while the Y13R mutant is completely random coil. The mutation sites are chosen to be uninvolved in strong interactions with the glucagon receptor in the active structure of the peptide. Therefore, these arginine mutants of glucagon are promising alternative compounds for treating hypoglycemia.

Structural Refinement of Glucagon for Therapeutic Use

Glucagon counters insulin's effects on glucose metabolism and serves as a rescue medicine in the treatment of hypoglycemia. Acute hypoglycemia, a common occurrence in insulin-dependent diabetes, is the central obstacle to correcting high blood glucose, a primary cause of long-term microvascular complications. As a result, there has been a resurgence of interest in improved glucagon therapy, including nonconventional liquid formulations, alternative routes of administration, and novel analogs with optimized biophysical properties. These options collectively minimize the complexity of glucagon delivery and enable its application in ways not feasible with conventional emergency rescue kits. These advances have indirectly promoted the integrated use of glucagon agonism with other hormones in a manner that runs counter to the long-standing pursuit of glucagon antagonism. This review summarizes novel approaches to glucagon optimization, methods with potential application to the broader family of therapeutic peptides, where biophysical challenges may be encountered.

Max Bergmann award lecture:Macromolecular medicinal chemistry as applied to metabolic diseases

This review presents the scope of research presented in an October 2016 lecture pertaining to the award of the 2015 Max Bergmann Medal. The advancement in synthetic and biosynthetic chemistry as applied to the discovery of novel macromolecular drug candidates is reviewed. The evolution of the technology from the design, synthesis, and development of the first biosynthetic peptides through the emergence of peptide-based incretin agonists that function by multiple biological mechanisms is exemplified by the progression of such peptides from preclinical to clinical study. A closing section highlights recent progress made in total chemical synthesis of insulin and related peptides.