Preparation Of Clustered Ultrasmall Iron Oxide Nanoparticles Loaded With Gossypol For Theranostics Of Tumors

Cancer has become one of the leading causes of human death.However,chemotherapy,a widely used treatment strategy as traditional systemic therapy,suffers from low drug penetration and inherent or acquired resistance.The rapid development of nanotechnology has made precise diagnosis and efficient treatment of tumors possible.For example,nanomaterials can themselves be used as novel and efficient diagnostic/therapeutic agents,and also be applied as carriers to load other diagnostic/therapeutic agents to overcome agent’s insolubility in water and less enrichment in lesions caused by the body’s physiological barriers.More importantly,multiple diagnostic/therapeutic agents can be integrated into one nanoplatform to implement theranostics.Among numerous nanomaterials,ultra-small iron oxide nanoparticles（USIO NPs）can not only be used for magnetic resonance（MR）imaging diagnosis,and to catalyze H₂O₂ at the tumor site to generate reactive oxygen species（ROS）for chemodynamic therapy,but also be constructed into nanoclusters（NCs）through appropriate design to load other diagnostic or/and therapeutic agents（such as chemotherapeutics）for single-modal or dynamic MR imaging,multi-modal imaging,and imaging-guided precision therapy.However,the current nanoplatforms based on USIO NCs usually are synthesized by several complex processes,which are not conducive to clinical translation or have only simple functions.Therefore,the construction of easy-to-prepare,especially tumor-microenvironment-responsive,smart USIO NCs remains a great challenge.Based on these,in this study ROS-responsive USIO NCs were constructed through the coupling of boronic acid ester bonds between phenylboronic acid（PBA）and the chemotherapeutic drug gossypol for MR imaging-mediated chemotherapy/chemodynamic therapy of breast cancer（4T1）tumor model with enhanced USIO NC enrichment in tumor sites through ultrasound targeting microbubble destruction（UTMD）technology.First,citric acid-stabilized USIO NPs were synthesized by solvothermal method,and ethylenediamine was modified on their surface by EDC chemistry.Then PBA was further conjugated on it by substitution reaction,and finally gossypol-loaded clusters（G-USIO NCs）were formed by coupling gossypol with USIO NPs.G-USIO NCs was able to dissociate Fe²⁺in the weakly acidic tumor microenvironment,and Fenton reaction occurred when Fe²⁺reacted with H₂O₂ at a high concentration inside the tumor to generate·OH,cleaving the boronate bond to further release gossypol to implement tumor-microenvironment responsive chemodynamic therapy and chemotherapy.The results showed that the prepared G-USIO NCs with a size of 197.1nm had good biocompatibility,colloidal stability and imaging ability(r₁=0.7 m M^-1s^-1);the intracellular ROS,LPO,GSH,related apoptotic proteins（Bcl-2,Bax,P53,PTEN）and apoptosis levels of 4T1 cells treated with G-USIO NCs confirmed that it has a good inhibitory effect on the growth of 4T1 cells;combined with UTMD technology,the treatment and imaging effects were significantly enhanced(r₁=1.1m M^-1s^-1);after intravenous injection,enhanced T₁ MR imaging was achieved at the subcutaneous 4T1 tumor site of mouse,and the tumor growth and metastasis were significantly inhibited.In conclusion,combined with UTMD technology,the prepared G-USIO NCs are expected to perform efficient treatment of different tumors,providing new ideas for the development of novel smart nanoplatforms for accurate diagnosis and efficient treatment of tumors.