Rationally designed, nontoxic, nonamyloidogenic analogues of human islet amyloid polypeptide with improved solubility

Human islet amyloid polypeptide (hIAPP or amylin) is a polypeptide hormone produced in the pancreatic β-cells that plays a role in glycemic control. hIAPP is deficient in type 1 and type 2 diabetes and is a promising adjunct to insulin therapy. However, hIAPP rapidly forms amyloid, and its strong tendency to aggregate limits its usefulness. The process of hIAPP amyloid formation is toxic to cultured β-cells and islets, and islet amyloid formation in vivo has been linked to β-cell death and islet graft failure. An analogue of hIAPP with a weakened tendency to aggregate, denoted pramlintide (PM), has been approved for clinical applications, but suffers from poor solubility, particularly at physiological pH, and its unfavorable solubility profile prevents coformulation with insulin. We describe a strategy for rationally designing analogues of hIAPP with improved properties; key proline mutations are combined with substitutions that increase the net charge of the molecule. An H18R/G24P/I26P triple mutant and an H18R/A25P/S28P/S29P quadruple mutant are significantly more soluble at neutral pH than hIAPP or PM. They are nonamyloidogenic and are not toxic to rat INS β-cells. The approach is not limited to these examples; additional analogues can be designed using this strategy. To illustrate this point, we show that an S20R/G24P/I26P triple mutant and an H18R/I26P double mutant are nonamyloidogenic and significantly more soluble than human IAPP or PM. These analogues and second-generation derivatives are potential candidates for the coformulation of IAPP with insulin and other polypeptides.