Protein PEGylation for cancer therapy: bench to bedside

Abstract

PEGylation is a biochemical modification process of bioactive molecules with polyethylene glycol (PEG), which lends several desirable properties to proteins/peptides, antibodies, and vesicles considered to be used for therapy or genetic modification of cells. However, PEGylation of proteins is a complex process and can be carried out using more than one strategy that depends on the nature of the protein and the desired application. Proteins of interest are covalently conjugated or non-covalently complexed with inert PEG strings. Purification of PEGylated protein is another critical step, which is mainly carried out based on electrostatic interactions or molecular sizes using chromatography. Several PEGylated drugs are being used for diseases like anemia, kidney disease, multiple sclerosis, hemophilia and cancers. With the advancement and increased specificity of the PEGylation process, the world of drug therapy, and specifically cancer therapy could benefit by utilizing this technique to create more stable and non-immunogenic therapies. In this article we describe the structure and functions of PEGylation and how this chemistry helps in drug discovery. Moreover, special emphasis has been given to CCN-family proteins that can be targeted or used as therapy to prevent or block cancer progression through PEGylation technology.

Keywords: Cancer; Immunogenicity; Nanoparticles; PEGylation; Polyethylene glycol.

Fig. 1

(a). Poly ethylene glycol with the most frequently used end groups, diol on top, and methoxy PEG at the bottom panel. (b). First generation PEGylation using cyanuryl chloride as coupling agent

Fig. 2

Common end groups that are available for PEGylation of proteins and different substrates

Fig. 3

Activation of carboxylic end groups of PEGS for coupling to N-terminal of peptides. This coupling chemistry belong to the so-termed ‘first generation’ PEGylation strategy

Fig. 4

Common PEGylation of proteins using canonical amino acids

Fig. 5

(a). Enzymatic ligation of PEG to glutamine residue of a protein, and (b). Attachment of cleavable PEG to a protein which is capable of releasing the active protein upon hydrolysis

Fig. 6

(a). Thiol reactive PEGs for site-specific PEGylation of proteins containing cysteine residue. (b). CuAAC PEGylation of human superoxide dismutase1, and (B) SPAAC PEGylation of lipase CalB

Fig. 7

Reductive amination of CCN5 using mPEG propionaldehyde of different molecular weight resulted in PEGylated CCN5, which extended the biological half-life of the protein