Folate receptor mediated intracellular protein delivery using PLL–PEG–FOL conjugate

Abstract

To develop a receptor-mediated intracellular delivery system that can transport therapeutic proteins or other bioactive macromolecules into a specific cell, a di-block copolymer conjugate, poly( l-lysine)–poly(ethylene glycol)–folate (PLL–PEG–FOL), was synthesized. The PLL–PEG–FOL conjugate was physically complexed with fluorescein isothiocyanate conjugated bovine serum albumin (FITC-BSA) in an aqueous phase by ionic interactions. Cellular uptake of PLL–PEG–FOL/FITC-BSA complexes was greatly enhanced against a folate receptor over-expressing cell line (KB cells) compared to a folate receptor deficient cell line (A549 cells). The presence of an excess amount of free folate (1 mM) in the medium inhibited the intracellular delivery of PLL–PEG–FOL/FITC-BSA complexes. This suggests that the enhanced cellular uptake of FITC-BSA by KB cells in a specific manner was attributed to folate receptor-mediated endocytosis of the complexes having folate moieties on the surface. The PLL–PEG–FOL di-block copolymer could be potentially applied for intracellular delivery of a wide range of other biological active agents that have negative charges on the surface.