Tailor-made self-assembling block copolymers to build multifunctional nanoparticles

This work is based on the development of a simple and elegant route of synthesis for poly(ethylene glycol)-poly(??caprolactone) (PEG-PCL) diblock copolymers tailed with an azido group, useful for conjugation with opportunely modified molecules of biological interest. The purpose is to improve the targeting ability of nanoparticles (NPs) prepared by self-assembling of these copolymers. Initial tailoring of PEG is performed through a method that allows selective introduction of functional groups at only one end1. In step 1, the use of a proper catalyst fully avoids formation of bifunctional PEG, as confirmed through 1H-NMR : N3PEG-PCL is synthesized through ring opening polymerization (ROP) of CL initiated by the -OH of N3PEG. The azido group has then been used in Copper-catalyzed Azide-Alkyne Cycloaddition "click" reaction. Click reactions are highly selective, do not produce by-products and require mild conditions. The reaction was successfully performed with copper wires as catalyst. An example of molecule "clicked" through this route is folic acid, one of the most extensively employed targeting moieties to enhance nanocarrier accumulation in cancer cells. Folic acid was previously modified with propargylamine through carbodiimide chemistry to introduce an alkyne group. A systematic study of the reaction through HPLC and mass spectroscopy allowed to select the optimal reaction conditions in order to minimize formation of ?-conjugate and by-products.2 Fol-PEG1500-PCL4000 was used in various percentages with PEG1000-PCL4000 or PEG2000-PCL4000 to prepare NPs by nanoprecipitation technique. The use of PEG blocks with different lengths is expected to vary the exposition of folate on NP surface. In order to track NP inside cells, both non-folate copolymers were conjugated with Rhodamine B as a fluorescent probe through the terminal hydroxyl of PCL block. Preliminary in vitro uptake studies in cells overexpressing folate receptor demonstrate a higher extent of uptake for NPs exposing folate on short PEG blocks due to receptor-mediated endocytosis. Acknowledgments The financial support of AIRC IG 2014 #15764 is gratefully acknowledged.