Mannose Modified Polymeric Nanomicelles Conjugated With Bodipy-based For Targeted Photodynamic Therapy

The application of photodynamics in the treatment of cancer,which destroys diseased tissue through photodynamic reactions to achieve the goal of cancer treatment,has attracted much attention in the field of biological research.However,the lack of hydrophobicity and targeting property of photosensitizer limits of its application in photodynamic therapy,resulting in its low biological utilization in the body and difficult to gather in the tumor site.It is necessary to find a carrier to deliver the photosensitizer to the tumor site specifically,in order to improve the biocompatibility of the photosensitizer and enhance its therapeutic effect on cancer.Among a variety of nanocarriers,polymeric micelles are favored by researchers for their potential application value and unique properties.In order to overcome the defects of photosensitizer in photodynamic therapy and achieve desired therapeutic effect,targeting molecules can be conjugated on the surface of polymeric micelles,which are able to recognise and target tumor cells.In this study,block copolymer(Pt BA-b-PGMA)were prepared by two step atom transfer radical polymerization(ATRP).Then,the tert butyl ester on the polymer fragment Pt BA was removed by hydrolysis to form block copolymer with carboxyl group PAA-b-PGMA.Mannose modified block copolymers Mannose-PAA-b-PGMA were prepared by amide condensation in which the pre-prepared amino acid with amino terminal group was modified on polymer.After that,the modified block copolymer Mannose-PAA-b-PGMA-N3 with azido group is formed during the ring opening reaction of epoxy groups on the block polymer fragment PGMA in the presence of sodium azide.Finally,with azide groups on block polymers and fluorinated molecular boron two pyrrole with alkyne group(BODIPY)which was prepared before,the "click" reaction was carried out in the presence of sodium ascorbate and copper sulfate pentahydrate.We successfully prepared the surface mannose modified polymeric micelles,which is covalently linked BODIPY photosensitizer(Mannose-PAA-b-PGMA-BODIPY).The structure of Mannose-PAA-b-PGMA-BODIPY was confirmed by 1 NMR spectroscopy and Fourier transform infrared spectroscopy,and its size and morphology were investigated by transmission electron microscopy and dynamic light scattering.The results showed that the polymer micelles prepared by the mannose modified photosensitizer were spherical with uniform size distribution and good stability.The formation of singlet oxygen was measured by Agilent Cary Eclipse fluorescence spectrophotometer,results indicated that polymeric micelles of the photosensitizer were capable of continuously producing singlet oxygen under the irradiation of specific wavelengths of light.The breast cancer MDA-MB-231 tumor cells and HEK293 normal cells were used as cell models,and the mannose receptor targeting effect and photodynamic therapy efficacy of the two cells were investigated by laser confocal microscopy.It turned out that polymeric micelles can be specifically rocognised by over-expressed mannose receptors on MDA-MB-231 tumor cells and then enter cancer cells by endocytosis.Man-PAA-b-PGMA-BODIPY did not exhibit toxicity against MDA-MB-231 and HEK293 cells in the dark,while enhanced phototoxicity was observed on MDA-MB-231 cancer cells under 535 nm LED irradiation.Finally,the biocompatibility and cytotoxicity of polymeric micelles were evaluated by MTT cytotoxicity assay,the experimental results indicated that polymeric micelles were of good biocompatibility,they showed greater toxicity toward tumor cells while there was no toxic effects on normal cells.The present study demonstrates that Mannose-PAA-b-PGMA-BODIPY is expected to be a promising photosensitizer for cancer treatment.