Background: Although various injected peptide and protein therapeutics have been developed successfully over the past 25 years, several pharmacokinetic and immunological challenges are still encountered that can limit the efficacy of both novel and established biotech molecules. Objective and method: PEGylation is a popular technique to address such properties. PEGylated drugs exhibit prolonged half-life, higher stability, water solubility, lower immunogenicity and antigenicity, as well as potential for specific cell targeting. Although PEGylated drug conjugates have been on the market for many years, the technology has steadily developed in respect of site-specific chemistry, chain length, molecular weights and purity of conjugate. These developments have occurred in parallel to improvements in physicochemical methods of characterization. Conclusion: This review will discuss recent achievements in PEGylation processes with an emphasis on novel PEG-drugs constructs, the unrealized potential of PEGylation ...

In its 33 years, ADDR has published regularly on the potential of oral delivery of biologics especially peptides and proteins. In the intervening period, analysis of the preclinical and clinical trial failures of many purported platform technologies has led to reflection on the true status of the field and reigning in of expectations. Oral formulations of semaglutide, octreotide, and salmon calcitonin have completed Phase III trials, with oral semaglutide being approved by the FDA in 2019. The progress made with oral peptide formulations based on traditional permeation enhancers is against a background of low oral and variable bioavailability values of ~1%, leading to a current perception that only potent peptides with a viable cost of synthesis can be realistically considered. Desirable features of candidates should include a large therapeutic index, some stability in the GI tract, a long elimination half-life, and a relatively low clearance rate. Administration in nanoparticle formats have largely disappointed, with few prototypes reaching clinical trials: insufficient particle loading, lack of controlled release, low epithelial particle uptake, and lack of scalable synthesis are being the main reasons for discontinuation. Disruptive technologies based on engineered devices promise improvements, but scale-up and toxicology aspects are issues to address. In parallel, medicinal chemists are synthesizing stable hydrophobic macrocyclic candidate peptides of lower molecular weight with potential for greater oral bioavailability than linear peptides, but without a requirement for elaborate drug delivery systems. In summary, while there have been advances in understanding the limitations of peptides for oral delivery, low membrane permeability, metabolism, and high clearance rates continue to hamper progress.

Salcaprozate sodium (SNAC) and sodium caprate (C₁₀) are two of the most advanced intestinal permeation enhancers (PEs) that have been tested in clinical trials for oral delivery of macromolecules. Their effects on intestinal epithelia were studied for over 30 years, yet there is still debate over their mechanisms of action. C₁₀ acts via openings of epithelial tight junctions and/or membrane perturbation, while for decades SNAC was thought to increase passive transcellular permeation across small intestinal epithelia based on increased lipophilicity arising from non-covalent macromolecule complexation. More recently, an additional mechanism for SNAC associated with a pH-elevating, monomer-inducing, and pepsin-inhibiting effect in the stomach for oral delivery of semaglutide was advocated. Comparing the two surfactants, we found equivocal evidence for discrete mechanisms at the level of epithelial interactions in the small intestine, especially at the high doses used in vivo. Evidence that one agent is more efficacious compared to the other is not convincing, with tablets containing these PEs inducing single-digit highly variable increases in oral bioavailability of payloads in human trials, although this may be adequate for potent macromolecules. Regarding safety, SNAC has generally regarded as safe (GRAS) status and is Food and Drug Administration (FDA)-approved as a medical food (Eligen^®-Vitamin B₁₂, Emisphere, Roseland, NJ, USA), whereas C₁₀ has a long history of use in man, and has food additive status. Evidence for co-absorption of microorganisms in the presence of either SNAC or C₁₀ has not emerged from clinical trials to date, and long-term effects from repeat dosing beyond six months have yet to be assessed. Since there are no obvious scientific reasons to prefer SNAC over C₁₀ in orally delivering a poorly permeable macromolecule, then formulation, manufacturing, and commercial considerations are the key drivers in decision-making.