Preparation And Application Of Novel Boron Delivery Agents For Boron Neutron Capture Therapy

Boron neutron capture therapy?BNCT?,as a new dual tumor-targeted radiation therapy modality,has significant advantages over traditional radiotherapy and chemotherapy.BNCT presents better therapeutic potential for primary or recurrent malignancies that are ineffective for conventional therapies.The development of novel boron delivery agents for BNCT therapy has always been a prerequisite for BNCT research.Therefore,in this paper,the preparation of four categories of novel boron delivery agents were systematically investigated as well as the in vitro cytotoxicity and tumor cell selectivity,the in vivo distribution and systemic toxicity were evaluated.Meanwhile,the efficacy and mechanism of the novel boron delivery agents for the treatment of tumors through BNCT in vitro were preliminarily explored.The main contents and results are as follows:1.A series of novel amphiphilic carborane compounds with lipid solubility and water solubility were synthesized.Through in vitro tumor cell selectivity and cytotoxicity screening,3,5-bis-oxy-methylene-carborane benzoic acid?compound 1?showed the ability to deliver ¹⁰B atoms to HepG2 cells with high selectivity and less cytotoxic,making it an ideal new boron delivery agent for BNCT therapy.Meanwhile,the HepG2 cells treated with compound 1 during BNCT could cause overexpression of ROS levels in tumor cells and then induce obvious apoptosis of the tumor cells.During BNCT,the number of DNA double-strand breaks in the tumor cells after compound 1 treatment was significantly increased,and the DNA damage in the tumor cells could not be effectively repaired.In addition,after BNCT treatment,the expression of cytokines PI3K,Akt and NF-?B related to growth signaling pathways in residual tumor cells were inhibited,indicating that BNCT treatment could not only effectively kill tumor cells but also inhibit the growth of residual tumor cells.2.A series of novel carborane compounds based on COX-2 inhibitors were synthesized.Among them,N,N-bis-methylene-carborane celecoxib?compound 1?showed high boron loading,high COX-2 selective inhibition and low cytotoxicity.Meantime,the compound 1 showed higher selectivity and intracellular uptake capacity for CAL 27 cells.In addition,the cytoskeleton of CAL 27 cells treated with compound 1 during BNCT were changed,and the migration capacity of cancer cells were weakened.The CAL 27 cells treated with compound 1 during BNCT could produce a large amount of ROS,the expression of pro-apoptotic protein Bax was up-regulated,while the expression of anti-apoptotic protein Bcl-2 was down-regulated,thereby activating the expression of caspase-3 and leading to irreversible programmed apoptosis of tumor cells.Meanwhile,the CAL 27 cells treated with compound 1 in BNCT could play a tumor therapeutic role by promoting DNA double-strand breaks and inhibiting the MAPKs signaling pathway.3.A novel hepatocellular carcinoma targeted PEGylated galactose micelle containing carborane clusters was developed.The micelle had the high selectivity and low cytotoxicity to HepG2 cells(IC₅₀>1000?M),and the micelle had the higher uptake in HepG2 cells than the positive control group sodium borocaptate?BSH?in vitro.The micelle-treated HepG2 cells during BNCT,the migration was reduced,and could exert a curative effect by damaging DNA double strands and inducing cancer cells apoptosis.Meanwhile,when administered to tumor-bearing mice with the micelle for 24 h,the concentration of ¹⁰B in tumor tissues was 5.0 times that of the BSH group.After 24 h of the micelle administration,the tumor/blood ratio of ¹⁰B concentration exceeded 25,and the ratio of ¹⁰B content of tumor/liver tissue was greater than 4.In addition,in normal mice,the micelles were mainly distributed in liver and kidney tissues,and the micelles could be effectively eliminated from normal tissues?liver,kidney and spleen?within 24 h,while the systemic toxicity was low.4.A novel tumor microenvironment-responsive and carborane-loaded hollow mesoporous silica nanomaterial with liver cancer targeting,anti-inflammatory,and antioxidant effects was developed.The nanostructure of the nanomaterial was stable under physiological conditions,which could effectively prevent the leakage of the loaded carborane.In the tumor microenvironment,under the dual stimulation of pH and GSH,the nanomaterial could open the mesopores and effectively release the loaded carborane to achieve the tumor therapeutic effect through BNCT.The nanomaterial could be effectively eliminated from normal tissues?heart,liver,spleen,lung and kidney?within 24 h in vivo without toxicity to normal tissues(LD₅₀>5000mg/kg).Meanwhile,the nanomaterial could inhibit the expression of iNOS and up-regulate the expression of Arg-1 and IL-10 in vivo,it could stimulate macrophages and make macrophages polarized into M2 type to exert anti-inflammatory effects.In addition,the nanomaterial had antioxidant activity,which could alleviate oxidative damage in normal cells by reducing ROS levels and increasing SOD enzyme activity.This paper provided the potential novel boron delivery agents for BNCT treatment,explored the tumor treatment mechanism of BNCT,provided the theoretical basis for the application of the novel boron delivery agents in BNCT,provided new strategies and methods for the development of novel boron delivery agents with tumor targeting and selectivity,and promoted the application and development of BNCT.