Study Of Polymeric Micelle Drug Delivery System Based On The Amphiphilic Polyphosphazene Containing Poly(NIPAm-co-DMAA) As A Segment

By changing the molar ratio of hydrophilic and hydrophobic segement,a series of novel amphiphilic graft polyphosphazenes were synthesized via thermal ring-opening polymerization and subsequent two-step substitution reaction of hydrophilic poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide)(Poly(NIP-Am-co-DMAA)) and hydrophobic ethyl glycinate(GlyEt).FTIR and ~1H NMR studies confirmed that copolymers were synthesized successfully.The molar ratio of the segment Poly(NIPAm-co-DMAA) to GlyEt was respectively 5.78:4.22,2.22: 7.78 and 1.42:8.58 responding to PNDGP-1,PNDGP-2 and PNDGP-3. Micellization behavior of PNDGPs in an aqueous phase was characterized by fluorescence technique,dynamic light scattering(DLS) and Partie Temperture Controller.The critical micelle concentra- tion(CMC) of the graft copolymer in aqueous solution was 0.281,0.178 0.035g/L,and the results revealed that with the hydrophobic content in amphiphilic copolym- ers increasing,the CMC decreased. The number-averaged particle size of spherical polymeric assemblies was nearly 20-50nm with a narrow distribution.The lower critical solution temperature(LCST) of all the polymer are higher than 37℃.Antitumor drug doxorubicin(DOX) was physically loaded into micelles prepared by dialysis and O/W emulsion method.We optimized the preparation condition by changing the DOX feeding,O/W volume ratio and polymer concentration in the O/W emulsion method.In dialysis method we optimized the preparation condition by changing the DOX feeding,initial water weight and polymer concentration and kind of solvent.In this study,we found that DOX loading efficiency increased with DOX feeding.Also diameters of DOX-loaded micelles increased as DOX loading content increasing.We found that copolymer with a high ratio of GlyEt,whose inner core was more hydrophobic,had higher loading efficiency.In vitro release of DOX compounds from the micelles was pH sensitive.With pH shifted from 5.5,6.5 to 7.4,the accumulative release weight of DOX increased. It offered a good opportunity to delivery antitumor drug to tumor tissue with lower leakage in circulation,and reduced the toxicity to normal tissue.The in vitro release profiles of DOX loaded micelles with different loading efficiency were studied.It was found that DOX loaded micelles with a high loading were released slower than the lower.It was due to the hydrophobic interaction enhanced by DOX loaded in the inner core.Copolymers with different composition had a slightly effect on the release profile of DOX loaded micelles.Micelles constructed by PNDGP-3 released DOX a little slower than that of PNDGP-2.The results of cytotoxicity study using an MTT assay method with Hela cell and HepG2 cell showed that amphiphilic graft polyphosphazenes had a good biocompatibility while exposure time had nearly no effect on the cell viability.DOX loaded micelles had nearly the same cell damage compared with unloaded free DOX. MTT assay with Hela and HepG2 both confirmed that cytotoxicity of DOX and DOX loaded micelles increased with time.We use the laser confocal scanning microscopy to observe the uptake of DOX of Hela cells and HepG2 cells.The results showed that the free DOX have been in the nucleus at 0.5h,while the three DOX-loaded micelles would be in the nucleus after 4h incubation.The in vivo pharmacokinetics in SD rats indicated that the DOX-loaded micelles can intended the half-life of DOX obviously and raised the area under curve(AUC) obviously and demonstrated the polymeric micelles had the long circulation ability.