Insulin self-association and the relationship to pharmacokinetics and pharmacodynamics

The treatment of type 1 diabetes requires multiple, daily injections of insulin. While many improvements involving formulation adjustments have been made in an attempt to optimize therapy, clinical experience indicates that the commercially available insulin preparations used for treatment have significant limitations. One principal deficiency relates to poor simulation of the physiological insulin secretion pattern, making achieving normalization of blood glucose concentrations difficult. Endogenous insulin secretion in nondiabetic subjects is characterized by a pulsatile profile that displays multiple, meal-stimulated phases and low basal concentrations between meals and overnight. Optimal diabetes therapy, therefore, requires insulin preparations that display a rapid onset of action with corresponding rapid clearance to provide for meal ingestion as well as preparations that can maintain a sustained, peakless profile for basal requirements. Recent efforts in pharmaceutical research have used the concept of rational-based design of the insulin molecule in an attempt to produce preparations that display more ideal pharmacological profiles. Using detailed structural information obtained from X-ray crystallographic studies to guide design strategies and exploit the nonrestrictive synthetic capabilities of recombinant DNA technology, researchers have prepared a number of insulin analogs that display a reduced propensity towards self-association. Clinical evaluations have shown that these so called "monomeric" analogs better mimic the meal-stimulated pharmacokinetics of insulin secretion observed in nondiabetics. Two monomeric insulin analog preparations have successfully obtained regulatory approval and are now commercially available. Efforts to produce optimized basal-acting insulin analogs have lagged behind. While some of these analogs have been engineered using recombinant DNA technology, design strategies in many cases exploit physicochemical properties of insulin other than self-association. One basal insulin analog has recently received regulatory approval. This paper reviews insulin self-association and its relationship to pharmacokinetics and pharmacodynamics. Particular emphasis is placed on the approaches used to manipulate self-assembly resulting in meal-time insulin analogs that display optimal pharmacological properties. Other design strategies used to develop improved basal insulin preparations are also considered.