PEGylation

PEGylation means attaching chains of polyethylene glycol — a flexible, water-loving polymer abbreviated PEG — to the surface of a drug carrier or a drug molecule. Picture wrapping a parcel in a layer of slippery, water-grabbing streamers: the streamers hold a cushion of water around the parcel that makes it harder for the body to grab, recognise and remove.

That watery cushion does several useful things. It hides the carrier from the proteins and immune cells that would otherwise tag it for clearance, so it circulates in the blood far longer; it reduces clumping and uptake by the liver and spleen; and for protein drugs it can lower immune reactions and slow breakdown. PEGylation is why many liposomes and lipid nanoparticles carry a polyethylene glycol coat.

PEGylation has known downsides. The same coat that hides a carrier can also block it from entering target cells — the so-called PEG dilemma — and repeated dosing can trigger anti-PEG antibodies that speed up clearance the second time, an effect linked to accelerated blood clearance. Choosing the right PEG length and surface density is a careful balancing act, not a simple add-on.