Effects of polymer terminal group inside micelle core on paclitaxel loading promoting and burst release suppressing

Paclitaxel (PTX) is widely used in the treatment of advanced esophageal and gastric cancer. Polymeric micelles can improve the drug-loading efficiency of PTX. However, the end groups on the amphiphilic blocks affect the drug-loading efficiency and the release kinetics of polymeric micelles. Therefore, there is an urgent need to disclose the tailoring of the core-/shell-forming terminal groups.

Different from the conventional block copolymer synthesis in the reversible addition-fragmentation chain-transfer polymerization, which has a hydrophilic end group on the core-forming blocks, an alternative monomer addition method was applied to tune and obtain two block copolymers with symmetrical and similar block length PBMA_n-b-PNAM_m [PNAM, poly(N-acryloylmorpholine); PBMA, poly(n-butyl methacrylate)] but distinct end groups on the hydrophobic core-forming blocks, that is, HOOC-PBMA-PNAM-Phen and HOOC-PNAM-PBMA-Phen. The chemical structure of the resulting copolymers was elucidated by proton nuclear magnetic resonance spectroscopy and differential scanning calorimetry. The spherical morphology revealed by transmission electron microscopy and the uniform particle size revealed by dynamic light scattering analysis clearly confirmed the successful preparation of a PTX-polymeric micelle complex.

The particle sizes of HOOC-PBMA-PNAM-Phen and HOOC-PNAM-PBMA-Phen were about 40 and 235 nm respectively. The PTX loading efficiency of HOOC-PBMA-PNAM-Phen was much lower than that of HOOC-PNAM-PBMA-Phen. The PTX release from HOOC-PBMA-PNAM-Phen was much slower than that of HOOC-PNAM-PBMA-Phen. The polymers had glass transition temperature (T_g) values of 70.24 and 74.22 ℃, which was from the HOOC-PBMA-PNAM-Phen and HOOC-PNAM-PBMA-Phen micelles, respectively. The systematic study on the PTX loading and releasing profile disclosed that, compared with the HOOC-PBMA-PNAM-Phen, the micelles with Phen group on the hydrophobic block (HOOC-PNAM-PBMA-Phen) enhanced drug loading and prolonged drug release but with a larger particle size.

The results indicated that the hydrophobic end group Phen on the core-forming blocks can promote hydrophobic drug loading and suppress burst release.