Hypoxia- And Singlet Oxygen- Responsive Multifunctional Micelles For Enhanced Photodynamic Anti-tumor Therapy

The nanotechnology-modified photodynamic therapy?PDT?for antitumor research has shown the advantages of low side effects,selectivity,repeatability,minimally invasiveness,and the enhanced permeability and retention effects?EPR effects?.However,it has been suffering from the limited agent dose accumulation in tumor,the very short half-life and limited diffusion radius of singlet oxygen?¹O2?in tumor.Herein,we report a dually hypoxia and singlet oxygen responsive polymeric micelles to efficiently utilize the photosensitizer deposited in the disease site and hence to facilely improve the therapeutic efficacy of PDT.The tailored methoxy poly?ethylene glycol?-azobenzene-poly?aspartic acid-imidazole?copolymer conjugate was synthesized.It contained the hypoxia responsive linker azobenzene and singlet oxygen sensitive group imidazole.The self-assembled conjugate micelles with the size of 189±19 nm could efficiently load the model photosensitizer,Chlorin e6?Ce6?with the drug loading efficiency at 4.1±0.5%?w/w?.The hypoxia responsive ability of the DR micelles was demonstrated by the changes of absorbance of azobenzene at the wavelength of 378 nm and the size of placebo polymer under hypoxic environment.Thereafter,the improved cellular uptake of micelles was achieved by the triggered azobenzene cleavage that provoked PEG shedding thereby the increased cell membrane affinity.The ¹O₂-responsive profile was revealed by size expansion in pH 7.4 and the corresponding rapid Ce6 release,which was enabled by imidazole structural change that caused by ¹O₂ under laser irradiation.In addition,the ¹O₂ mediated cargo release not only addressed the short half-life and limited diffusion radius of singlet oxygen,but also increased the extent of hypoxia,which could in turn enhance internalization of micelles and increase the intracellular Ce6 amount.The cellular uptake and cytotoxicity study was carried out in the Lewis lung carcinoma?LLC?cells.The cellular uptake study of fluorescence probe FITC-labeled placebo DR micelles as well as Ce6-loaded DR micelles both demonstrated that the DR micelles could deliver significantly more micelles to the cells in hypoxic environment than that in normoxic condition.This resulted in a substantially improved cytotoxicity induced by Ce6-loaded DR micelles in hypoxic environment compared with the Ce6-loaded SR micelles.It was consistent with the superior in vivo tumor inhibition ability of Ce6-loaded DR micelles in the LLC tumor-bearing mice.The enhanced PDT effect was observed by the superior inhibition of tumor growth,as well as histological and apoptosis analysis of tumor tissue.The current work presented a facile and robust nanoplatform to realize interactively triggered photosensitizer delivery and improved PDT efficacy.