Effects of LinTT1-peptide conjugation on the properties of poly(ethylene glycol)-block-(ε-caprolactone) nanoparticles prepared by the nanoprecipitation method

Functionalization of polymer nanoparticles (NPs) with targeting peptides is of interest for drug delivery applications to enhance tumor accumulation and penetration. Herein, we evaluated the feasibility of two different methods for the attachment of a tumor-penetrating peptide LinTT1 (AKRGARSTA) to poly(ethylene glycol)-block-poly(ε-caprolactone) (PCL-PEG) NPs: (1) “post-conjugation” onto pre-formed nanoparticles, and (2) “pre-conjugation”, the synthesis and purification of peptide-polymer conjugates and subsequent nanoprecipitation of the conjugates diluted with non-functionalized polymers. Conjugation of the labelled peptide via maleimide-thiol chemistry was verified by gel permeation chromatography (GPC) and fluorescence measurements. Characterization of NPs with respect to particle size, zeta potential, morphology and peptide content was performed, and their ability to bind to the target protein p32 was tested using a cell-free assay. Importantly, both methods resulted in NPs that were able to bind their target when methyl-terminated PCL-PEG used as the diluent polymer, but not when acid-terminated polymer was used. Moreover, peptide conjugation induced a morphological transformation from spheres to vesicles regardless of the conjugation method used. However, smaller and more homogeneous NPs were obtained by the pre-conjugation method.