Abstract
Peptides and proteins are attractive targets for therapeutic drug development due to their exquisite target specificity and low toxicity profiles. However, their complex structures give rise to several challenges including solubility, stability, aggregation, low bioavailability, and poor pharmacokinetics. Numerous chemical strategies to address these have been developed including the introduction of several natural and non-natural modifications such as glycosylation, lipidation, cyclization and PEGylation. Glycosylation is considered to be one of the most useful modifications as it is known to contribute to increasing the stability, to improve solubility, and increase the circulating half-lifves of these biomolecules. However, cellular glycosylation is a highly complex process that generally results in heterogenous glycan structures which confounds quality control and chemical and biological assays. For this reason, much effort has been expended on the development of chemical methods, including by solid phase peptide synthesis or chemoenzymatic processes, to enable the acquisition of homogenous glycopeptides to greatly expand possibilities in drug development. In this mini-review, we highlight the importance of such chemical glycosylation methods for improving the biophysical properties of naturally non-glycosylated peptides as applied to the therapeutically essential insulin and related peptides that are used in the treatment of diabetes.
Highlights
Proteins undergo several types of post-translational modifications (PTMs) of which glycosylation is the most abundant type among eukaryotes
We highlight the chemical nonnative glycosylation methods as applied to glucose homeostasis-regulating peptides involved in the treatment of diabetes including insulin, glucagon, glucagon-like peptide-1, and pramlintide
Pharmacokinetic studies in rat, mouse and dog models showed that the half-life of the insulin analogs increased greatly. They further studied the pharmacokinetic and pharmacodynamic properties of CarboCarrier R insulin analog modified at LysB29 (SCH 900948) in humans (Miltenburg et al, 2013) and their phase 1 studies confirmed an extended half-life when compared to endogenous insulin
Summary
Proteins undergo several types of post-translational modifications (PTMs) of which glycosylation is the most abundant type among eukaryotes. Semisynthesis involves both, the chemical synthesis of smaller peptide fragment with desired modification and recombinant expression of remaining larger fragment(s), exploiting the advantages of both the methods. A glycosylated amino acid building block can be directly incorporated during solid phase peptide synthesis (SPPS) or, alternatively, a short glycan is first introduced which is later extended by chemical or enzymatic methods (Unverzagt and Kajihara, 2018).
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