Preparation Of Oxygen-Generating Nano-System And Its Application In Tumor Therapy

Radiotherapy and chemotherapy are the most common approaches to solid tumor treatment.Many researches suggest that tumor hypoxic microenvironment is the vital factor for the limitation of therapeutic efficiency.In terms of radiotherapy,increasing DNA repair,augmenting hypoxia-inducible-factor-1(HIF-1)expression and inhibiting immune activation mainly mediate the resistance of tumor cells to radiation.For chemotherapy,solid tumor hypoxic microenvironment is closely related to the poor prognosis.The abominable conditions determine the increased level of HIF-1,decreased apoptosis and improved tendency of metastasis,which lead to the failure of chemotherapy.Therefore,enhancing tumor oxygenation for modifying tumor microenvironment attracts great interest from the fields of both radiotherapy and chemotherapy.Different from non-specific methods of tumor oxygenation,such as delivering perfluocarbon,hemoglobin,hyperbaric chamber,tumor microenvironment responsive oxygen-generation nano-system could realize tumor-specific oxygenation avoiding the potential of oxygen toxicity to normal tissues.As a result,tumor microenvironment responsive oxygen-generation nano-system could rebuild tumor microenvironment for enhancing the tumor killing of chemical drugs and radiation,and inhibiting the tendency of metastasis.Recently,manganese dioxide nanoparticles(MnO2-NPs)have been widely studied as a catalase-like nanoenzyme to decompose the overexpressed hydrogen peroxide within the tumor microenvironment into oxygen molecules.Moreover,these biocompatible MnO2-NPs take advantage of T1-weighted magnetic resonance imaging for tumor detection and image-guided therapy.Based on the key issues in the chemotherapy and radiotherapy,we design tumormicroenvironment-specific oxygen-generating nano-systems for integrating both hydrophobic and hydrophilic drugs with manganese dioxide in simple fabrication ways.The main research contents include the following two parts.(1)Manganese dioxide deposition on paclitaxel albumin for enhancing chemoradiation therapy.Paclitaxel is one of the most promising candidates combined with radiotherapy among the abundant chemotherapeutic agents.However,the characteristic abnormalities of tumor microenvironment with hypoxia and excess hydrogen peroxide(H2O2),tremendously limit the chemoradiation therapeutic efficacy of solid cancer.In addition,paclitaxel treatment stimulates tumor cells to generate H2O2 for tumor resistance.Notably,excess H2O2 in the tumor regions can stabilize hypoxia-inducible factor-1?(HIF-1?)by inhibiting prolyl hydroxylase(PHD).The increased expression of HIF-la enhances the function of P-gp to pump out paclitaxel.Additionally,hypoxic tumor cells become resistant to radiation therapy,where oxygen molecules can immobilize radiation-induced DNA damage and then prevent damaged DNA repair.Therefore,attractive benefits during tumor chemoradiation therapy will be achieved if excess H2O2 could be converted into oxygen.Taking advantage of the strong oxidation of KMnO4,we firstly deposited manganese dioxide on the surface of the albumin bound paclitaxel nanoparticles(ANPs-PTX)via a facile oxidation preparation to obtain MnO2 functioned ANPs-PTX(MANPs-PTX).After intravenous injection,MANPs-PTX could accumulate within the tumor regions via EPR effect and release Mn2+,oxygen and paclitaxel in response to tumor microenvironment including excess H2O2 and acidic pH.The improved tumor oxygenation could overcome the hypoxia of tumor and initiate HIF-1? degradation.Due to the decreased expression of P-gp,paclitaxel could retain in the tumor cells to suppress cell division via microtubulin inhibition.In presence of X-ray,abundant oxygen generation could induce more apoptosis,thus effectively enhance the therapeutic efficacy of chemoradiation therapy.Meanwhile,the released Mn2+ had excellent T1-MRI performances for tumor imaging.Additionally,MANPs-PTX exhibited no obvious toxicity to normal tissues.(2)Construction of nano-platform for hydrophilic drugs based on the structure of manganese dioxide for enhancing the efficacy of tumor therapy.In the previous work,we found that tumor oxygenation for HIF-1? degradation was insufficient,because the oxygen supply was transient due to the rapid oxygen consumption of proliferative cancer cells.Many sesearches suggest current tumor oxygenation agents including catalase,manganese dioxide,and perfluorocarbon nanoparticles,can only induce 25%-70%of HIF-1? degradation.The residual HIF-la will further dimerize with HIF-1? to form HIF-1 and initiate downstream gene transcription,including that of GLUT-1,PD-L1,and VEGF,which are mainly involved in cellular proliferation,immune exhaustion,and metastasis,respectively.Therefore,tumor oxygenation cooperation with residual HIF-1 functional inhibition is crucial to obtaining optimal radiation therapeutic outcomes.Acriflavine(ACF)is the most potent HIF-1 functional inhibitor among 3000 FDA approved drugs that prevents HIF-1?/? dimerization.Acriflavine is hydrophilic and cationic,and exhibits a short pharmacokinetic half-life,since the concentration of acriflavine in the blood decreases by 90%over 5 min after intravenous injection.The rapid clearance and poor tumor accumulation of acriflavine determine that repeated injections at a large dose offer mild tumor suppression.Therefore,integrating hydrophilic and cationic molecules like acriflavine into catalytic MnO2 nanoparticles in a simple way to improve their pharmacokinetic characteristics is an urgent challenge in the fields of both radiation therapy and drug delivery.Inspired by the application of MnO2 to eliminate metal cation pollution via electrostatic adsorption,we surprisingly found high affinity between anionic MnO2 nanoparticles and cationic small molecules(i.e.,the HIF-1 functional inhibitor acriflavine,photosensitizer methylene blue,immune agonist R837).For the first time,we established a reactive oxygen species(ROS)-responsive nanoplatform to successfully encapsulate hydrophilic and cationic acriflavine into MnO2 nanoparticles(ACF@MnO2).After accumulation within the tumor tissue,these nanoparticles could be efficiently endocytosed by tumor cells and mainly located within the lysosomes.Once reacted with H2O2 in the acidic conditions,Mn2+ was released within the tumor tissues for magnetic resonance imaging(MRI)to guide radiation therapy.The nanoparticles would then produce oxygen to relieve the hypoxic microenvironment and implement direct radiation sensitization.Meanwhile,the released acriflavine would gradually transfer into the cellular nucleus to inhibit HIF-1's transcription function to synergistically inhibit HIF-1 downstream signaling molecules(e.g.,PD-L1)against abscopal tumors.Our work thus presented an ROS-responsive nanoplatform with great efficiency for tumor oxygenation and HIF-1 functional inhibition to combat primary and metastatic tumors.In summary,focused on the key issues in the chemotherapy and radiotherapy,we designed tumor-microenvironment-specific oxygen-generating nano-systems for intergrating both hydrophobic and hydrophilic drugs with manganese dioxide.As a result,tumor oxygenation could significantly improve the therapeutic efficiency of chemotherapy and radiotherapy.Furthermore,aiming at the bottle neck of simple tumor oxygenation,we combined HIF-1 suppression with tumor oxygenation tactfully for inhibiting the progression of primary and metastatic tumors.The improved nanoplatform was universal to other various approaches of tumor therapies and provided new strategies for drug delivery,which could be easily transformed into clinical applications.