The immune system protects the body from disease by resisting the invasion of foreign molecules into its cells, for example, peptides and proteins are hydrolyzed by proteolytic enzymes; nucleic acids are hydrolyzed by nucleases, and most small molecules are eliminated in the liver and kidneys. This immune reaction protects the body from disease but can also cause many drugs to become inactive. PEG conjugation can shield antigenic epitopes of the protein, reduce degradation by proteolytic enzymes, enhance long-term stability and maintain or even improve pharmacokinetic and pharmacodynamics characteristics of the protein drug.
Image Source: sciencedirect.com
▶ PEGs are non-toxic, non-immunogenic, non-antigenic, highly water-soluble, and FDA approved synthetic polymer consisting of repeating ethoxy units: -(CH2 -CH2 -O)-.
▶ PEGylation, the covalent conjugation of a PEG derivative to another molecule, shows a decreased degradation by metabolic enzymes and a reduction or elimination of protein immunogenicity as the PEG coating prevents the approach or recognition by proteolytic enzymes and antibodies.
▶ Furthermore, PEGylation may favorably alter drug distribution in the organism.
▶ While PEGylation may improve the pharmacokinetic properties of a drug, the drug's main activity is predominantly preserved.
Based on molecular structure, PEG materials can be classified into three main categories: linear PEGs, multi-arm PEGs, and branched PEGs.
Common structures of PEGs: A) linear PEGs; B) multi-arm PEGs; and C) branched PEGs. Image Source: Material Matters
Linear PEGs such as methoxy PEGs (mPEGs), as well as hetero and homo-bifunctional PEGs, are used frequently for PEGylation of peptides, proteins, siRNA and modification of other small molecules, and for preparation of drug delivery systems such as nanoparticles. With this type of PEGs, proteins are conjugated in the distal end of a PEG molecule in a single attachment site. Bifunctional PEGs are linear PEGs with two available sites for protein conjugation, meaning that in maximum only two biomolecules may be conjugated, which limits the loading capacity comparing to the most recent PEG derivatives. Nonetheless, bifunctional PEGs may significantly increase viscosity compared to the originator drug formulation since one reactive PEG molecule can conjugate to two different protein molecules, resulting in protein cross linking and a hydrogel formation. In addition, linear PEGs of large molecular weight may impede the appropriate release of small molecular weight protein drugs, preventing them to reach therapeutic concentrations at the target sites.
Multi-arm PEGs are star-like structures carrying multi-hydroxyl or functional groups, increasing the amount of active sites and molecular weight. multi-arm PEGs are not much explored in the attachment with proteins due to protein cross-link. They have been widely investigated for conjugation of small molecule drugs such as NKTR-102 (PEG-irinotecan), EZN-2208 (PEG-SN38) and NKTR-214 (PEG- aldesleukin), which are some examples of PEGylated drugs that have entered into clinical trials.
Branched PEG derivatives, also known as "Y-shaped" PEG derivatives, contain two linear methoxy PEG chain attached to a central core. This structure provides better protection than linear PEGs toward antibodies recognition and cleavage by proteolytic enzymes. This PEG variant was tested in several proteins (i.e. ribonuclease, catalase, asparaginase, trypsin, among others), but is not applied as frequently for peptides and small molecules drugs.
Important applications of functionalized polyethylene glycols
▶ Preparation of graft polymeric supports for Solid-Phase Peptide Synthesis (SPPS)
▶ Introduction of solubilizing handles in SPPS
▶ Soluble polymer supports for Peptide Synthesis
▶ Soluble polymer supports for Organic Synthesis
▶ Introduction of hydrophilic amino acids in Peptide Synthesis
▶ Preparation of PEG-ligand conjugates for affinity partitioning of macromolecules
▶ Preparation of PEG-coated surfaces
▶ Linking of macromolecules to surfaces
▶ Synthesis of targetable polymeric drugs
▶ Preparation of PEG-glycoprotein conjugates
▶ Preparation of PEG-cofactor adducts for biorectors
Biochempeg offers a broad portfolio of PEG reagents with molecular weights up to 20 kDa for efficient PEGylations. Numerous homobifunctionalized, heterobifunctionalized, and mono-methoxy endcapped monofunctionalized linear PEG's are available in high quality. We provide polyethylene glycols activated for the most widely used conjugations to primary amines or thiols. The introduction of different protecting groups leads to extremely useful macromolecular cross-linking agents and spacers.