Coupling to Polymeric Scaffolds Stabilizes Biofunctional Peptides for Intracellular Applications

Here, we demonstrate that coupling to N-hydroxypropyl meth-acrylamide (HPMA) copolymer greatly enhances the activity of apoptosis-inducing peptides inside cells. Peptides correspond-ing to the BH3 domain of Bid were coupled to a thioester-activated HPMA (28.5 kDa) via native chemical ligation in a simple one-pot synthesis. Peptides and polymer conjugates were introduced into cells either by electroporation or by con-jugation to the cell-penetrating peptide nona-arginine. The mo-lecular basis of the increased activity is elucidated in detail. Loading efficiency and intracellular residence time were as-sessed by confocal microscopy. Fluorescence correlation spectroscopy was used as a separation-free analytical tech-nique to determine proteolytic degradation in crude cell lysates. HPMA conjugation strongly increased the half-life of the pep-tides in crude cell lysates and inside cells, revealing proteolytic protection as the basis for higher activity