Preparation And Performance Of Hypoxia-responsive Nanocarrier Drug Delivery System

The complex microenvironment of tumors provides an important idea for the development of nanocarriers.Utilizing the properties of hypoxia in the tumor core,hypoxic-responsive polymers have recently been used to develop intelligent nanocarrier for targeted and hypoxic-triggered drug delivery and controlled release.The hypoxia-responsive nanocarrier drug delivery systems can respond to the huge difference in oxygen content between tumor tissue and normal tissue.They maintain good stability under physiological conditions.However,the nanocarriers disintegrate in the hypoxic environment of the tumor,and the loaded drugs in the nanocarriers are specifically released in response to the tumor’s hypoxic microenvironment.The hypoxia-responsive nanocarrier drug delivery systems are expected to increase the drug concentration at the tumor site,enhance the anti-tumor effect of the drug,and reduce the toxic and side effects.The hydrophobic nitro groups in nitroimidazoles can be reduced to hydrophilic amino groups under hypoxic conditions,and this reaction is highly hypoxic-sensitive.Therefore,nitroimidazoles are widely used as hypoxic response elements to construct hypoxia-responsive nanocarrier.In this paper,three amphiphilic polymers containing nitroimidazole groups were synthesized,and hypoxia-responsive micelle drug delivery systems were constructed based on these polymers.Their structures and properties were characterized respectively,and hypoxia-responsive drug release properties of these micelles were demonstrated.It is expected to provide new ideas and an experimental basis for the development of hypoxia-responsive nanocarrier drug delivery systems.The main contents are as follows:(1)Preparation and properties of mucoadhesive hypoxia-responsive cationic polymeric micellesCationic polymers chitosan(CS)andε-polylysine(EPL)were grafted with hypoxia-responsive 6-(2-nitroimidazolium)caproic acid(NIHA),and chitosan derivative(CS-NID)andε-polylysine derivative(EPL-NID)with different degrees of substitution of NIHA were synthesized.Their structures were characterized by ~1H NMR,UV,FT-IR,and MS.The hypoxia-responsive CS-NID and EPL-NID micelles were prepared by ultrasonic method.The stability,mucoadhesion,hypoxia response,cytotoxicity,and drug release properties of the micelles were evaluated by DLS,Zeta potential,mucin-particle method,UV and cck-8.The results showed that the critical micelle concentrations(CMC)of both CS-NID and EPL-NID were lower than 0.05 mg/m L,which exhibited the strong micellization ability of both polymers in water.The spherical micelles with particle size less than 200 nm and high positive charge(Zeta potential>+30 m V)were prepared by self-assembly of CS-NID and EPL-NID in water.The micelles exhibited excellent storage stability,mucoadhesion,and sensitive hypoxia responsiveness.In vitro cytotoxicity results showed that CS-NID micelles exhibited excellent biocompatibility,and no loss of cell viability was observed at concentrations up to 400 ug/m L;EPL-NID micelles exhibited good biocompatibility at concentrations lower than 200 mg/m L,but only 67%of the cell viability was maintained when the concentration reached 400ug/m L.Doxorubicin(DOX)was encapsulated in micelles by the hydrophobic interaction,and the maximum drug loading content(DLC)and loading efficiency(DLE)of CS-NID micelles were 13.3%and 44.3%respectively.In vitro drug release showed that DOX was released from CS-NID micelles in a distinctly hypoxia-responsive manner.Only 42%of loaded Dox was released from the CS-NID micelles under normoxic conditions over 24h.Under hypoxic conditions,the CS-NID micelles were disintegrated due to the reduction of nitroimidazole groups to aminoimidazole,and the loaded DOX would be released rapidly.More than 65%of encapsulated DOX was released from the CS-NID micelles in 2h,and over 92%of DOX was released within 24 h under hypoxic conditions.(2)Synthesis of hypoxia-responsive PEG-b-P(MIs-co-MPC)copolymer and its application in drug controlled releaseThe PEG-b-P(MIs-co-MPC)block copolymer was synthesized by reversible addition-fragmentation chain transfer polymerization of 2-(2-methyl-5-nitro-1h-imidazol-1-yl)ethyl methacrylate(MI-MA)and 2-methylacryloxyethyl phosphate choline(MPC).The structure was characterized by NMR and GPC.PEG-b-P(MIs-co-MPC)micelles were prepared by ultrasonic method,and their size,stability,and hypoxic responsiveness were evaluated by DLS,Zeta potential,TEM,and UV.The PEG-b-P(MIs-co-MPC)micelles with spherical structure and uniform particle size of less than 20 nm exhibited excellent storage stability and sensitive hypoxia responsiveness.The controlled drug release in response to hypoxia was investigated by loading DOX in PEG-b-P(MIs-co-MPC)micelles.The micelles’drug loading efficiency(DLE)and drug loading capacity(DLC)were 82.1%and 16.4%,respectively.The hypoxic and p H-dependent drug release was observed in the micelles.DOX was rapidly released in hypoxic and acidic environments,with a maximum cumulative release of more than 61%,but less than 40%in normoxic conditions at p H=7.4.