PHEA-graft-polybutylmethacrylate copolymer microparticles for delivery of hydrophobic drugs.

Polymeric microparticles encapsulating two model hydrophobic drugs, beclomethasone dipropionate (BDP) and flutamide (FLU) were prepared by using the high pressure homogenization-solvent evaporation method starting from a oil-in-water emulsion. For the preparation of polymeric microparticles a α,β-poly(N-2-hydroxyethyl)-D,L-aspartamide (PHEA) graft copolymer with comb like structure was properly synthesized via grafting from atom transfer radical polymerization (ATRP) technique, by using two subsequent synthetic steps. In the first step a polymeric multifunctional macroinitiator was obtained by the conjugation of a proper number of 2-bromoisobutyryl bromide (BIB) residues to the PHEA side chains, obtaining the PHEA-BIB copolymer. PHEA-BIB copolymer was then used as macroinitiator for the polymerization via ATRP of the hydrophobic monomer such as butyl methacrylate (BMA) to obtain the α,β-poly(N-2-hydroxyethyl)-D,L-aspartamide-co-(N-2-ethylen-isobutyrate)-graft-poly(butyl methacrylate) copolymer (PHEA-IB-p(BMA)). Spherical microparticles with 1-3 microns diameter were prepared. Microparticles loaded with BDP or FLU were also prepared. In vitro mucoadhesion and enzymatic degradation studies evidenced bioadhesive properties and biodegradability of prepared microparticles, while release studies showed a different release profiles for the two loaded drugs: BDP was totally released from nanoparticles until 24h in pulmonary mimicking conditions; differently a slower FLU release rate was observed in gastro-intestinal mimicking conditions. The in vitro cytotoxicity activity was assessed using 16HBE and Caco-2 cell lines. Results showed that exposure of both cell lines to BDP-loaded microparticles do not inhibited the cell growth; on the contrary FLU-loaded microparticles inhibited the cell growth, in particular of the Caco-2 cancer cell line, in a concentration- and time-dependent manner. Finally, uptake studies demonstrated that BDP-loaded microparticles and FLU-loaded microparticles effectively increased uptake of loaded drugs in a time-dependent manner, respectively on 16HBE and Caco-2 cell lines.