Effects of charge and charge distribution on the cellular uptake of multivalent arginine-containing peptide-polymer conjugates.

Copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) and N-methacryloyl-β-alaninyl-S-benzyl thioester were prepared by employing free radical or RAFT conditions and denominated as "NCL polymers". The copolymer with a polydispersity index of 1.2-1.3 was used for the direct conjugation of unprotected peptides and peptide mixtures bearing differentially loaded side chains by native chemical ligation reactions conducted in aqueous buffer. Uptake into human HeLa cells was correlated with the overall surface charge and the ζ potentials of the peptide-polymer conjugates. Most notable were the differential effects found for various multivalent peptide-polymer conjugates containing arginine residues. Although positive ζ potentials were required for cellular uptake of the peptide-polymer conjugates, this sole charge effect was strongly dominated by the effect exerted by the relative distribution of arginine residues. Polymers conjugated with nona-arginine peptides were over-proportionally taken up, relative to their surface charge, compared to polymers with random distribution of single arginine residues. In view of these findings, peptide-polymer compositions suitable for efficient cellular uptake with negligible toxicity at polymer concentrations relevant for intracellular functional studies were determined.