Design of Insulin Variants for Improved Treatment of Diabetes - Peptide and Protein Design for Biopharmaceutical Applications - page 263

7.6 FAST-ACTING INSULINS

For reasons of storage stability, commercial insulins are administered
as Zn(II) hexamers [119]. The high stability of the native insulin hex-
amers, like pig and human insulin hexamers, results in relatively slow
dissociation and absorption of insulin upon injection in the subcuta-
neous tissue. Native insulins must therefore be dosed ½-1 hour before a
meal in order to match the increase in blood glucose after a meal
[31,32]. This timing can be difficult to get right. Scientists have worked
on this problem by engineering insulins which form less stable hexam-
ers, and thus provide faster absorption from the subcutaneous tissue.
The first results were published by Novo in the mid-1980s [120]. By
examining the insulin dimer and hexamer interfaces in insulin crystal
structures and inserting charge repulsions or steric repulsions at stra-
tegic positions (Figure 7.10), it was shown to be possible to design
insulins that form less stable oligomers. The design process excluded
the residues putatively involved in insulin-insulin receptor contacts, in
order to seek preservation of the biological activity of insulin. Clinical
investigations confirmed faster onset of action with the
oligomer-destabilized insulins [121,122]. The AspB10 analogue, alias
X10, was one such mutant displaying weaker oligomer stability, and
this analogue was brought to clinical trials. Unfortunately, animal
toxicology studies of AspB10 human insulin showed formation of
tumours [123], and the development of X10 was stopped. The toxicol-
ogy of AspB10 has been suggested to reside with its increased affinity
for the IGF receptor [124-126]. Meanwhile, Eli Lilly had started devel-
opment of their version of hexamer-destabilized fast-acting insulin.
Lilly went through clinical development faster, and therefore became
the first to reach the market with their variant, LysB28 ProB29 human
insulin , alias insulin lyspro ,alias Humalog , in 1996. The insulin lyspro
sequence was designed by considering the C-terminal part of the
B-chain of IGF-1, inspired by the observation that IGF-1 does not
form stable hexamers [127].
Novo Nordisk managed to find an alternative to AspB10, namely
AspB28 human insulin , alias X14 , alias insulin aspart , alias
NovoRapid , alias Novolog , which passed the clinical trials and reached
the market in 1999.
Although insulin lyspro and insulin aspart are often titillated mono-
meric insulins , they are in fact Zn(II) hexamers in the storage vials (crucial
for storage-stability reasons), but the hexamers are obviously destabilized
compared to regular insulin.