Construction And Application Of Light-controlled Polymer Prodrugs Delivery System

Cancer,the number one killer of human life and health,has attracted widespread attention.Despite the promising progress in the treatment of cancer,the cure rate of cancer is still limited.Chemotherapy is currently the common means of tumor treatment in clinical practice.Due to the unique physiological properties of tumor vasculature,nanodrug delivery systems,typically 50 to 150 nm,can be passively enriched in tumor tissue through enhanced permeability and retention（EPR）effect.Polymeric micelles with well-defined core-shell structures can improve the solubility,bioavailability and circulating half-life of hydrophobic drugs,making them a very promising nano-delivery system for cancer therapy.To achieve controlled drug release in tumor cells,researchers have begun to explore the introduction of chemical bonds with tumor microenvironmental responses（p H response,reduction response,enzyme response,and ROS response,etc.）between drugs and polymers to obtain polymeric pre-drug delivery systems that can accurately control drug loading and increase drug solubility and stability.However,insufficient drug loading remains one of the major challenges for polymeric micelles in drug delivery systems due to the typically low drug loading and encapsulation rates（less than 10%）of small hydrophobic drugs loaded by amphiphilic polymers.In addition,monotherapy is not as effective as they could be in practice,combination therapy offers the opportunity to obtain better therapeutic results and reduce side effects.For example,when photodynamic therapy（PDT）is used in combination with chemotherapy,it not only enhances the immune response by triggering acute inflammation and leukocyte infiltration,but also reduces the resistance of tumor cells to chemotherapeutic agents.To enhance drug delivery,controlled release of chemotherapeutic agents and PDT/chemotherapy synergy to enhance tumor treatment.Therefore,in this paper,we construct a series of polymeric pre-drug delivery systems with tumor microenvironment responsiveness have been constructed.First,a novel polymer prodrug delivery system with high drug loading and excellent stability,di P@PSSP,is constructed.di P@PSSP is self-assembled from a reduction-responsive star-shaped polymeric paclitaxel prodrug（4-arm-PEG-SS-PTX,PSSP）and a reduction-responsive dimer（PTX-SS-PTX,di PTX）.Di P@PSSP micelles have a PTX loading capacity of up to 46.9%and are very stable under normal physiological conditions,the nanoparticle size can be kept almost constant within 20 days.The controlled and complete release of paclitaxel（PTX）at high concentrations of glutathione（GSH）is achieved due to the disulfide bond in the polymeric precursor and dimer.After co-incubation of di P@PSSP micelles with erythrocytes for 6 h,the cell morphology remained intact and the hemolysis rate was less than 5%,showing good biocompatibility.In addition,di P@PSSP 114.3 nm±2.1（PDI=0.219±0.016）,which is favorable for tumor cells to passively target the uptake of nanodrugs through the EPR effect,is affected by the intracellular reducing environment and the disulfide bond is immediately broken,releasing high concentrations of PTX,which is released to disrupt the dynamic balance of microtubule polymerization-depolymerization,inhibit mitosis and induce apoptosis,showing good therapeutic effects in He La cells.The therapeutic effect of single chemotherapy is still unsatisfactory,and the introduction of a photosensitizer on top of the prodrug can achieve cascade amplification of combined therapy.Therefore,a novel photocontrolled polymer prodrug delivery system with ROS-sensitive and cascade amplification,Ce6@PTP/DP,was constructed.The delivery system was obtained from a ROS-responsive PTX prodrug,the conventional photosensitizer Chlorin e6（Ce6）,and doping the polymer DSPE-PEG.The nanomicelles exhibit extreme sensitivity due to the TK bond and Ce6,which is rapidly destabilized under H₂O₂ or light conditions.With appropriate particle size and good biocompatibility,the micelles can smoothly pass through the blood circulation to the tumor site and then be well taken up by tumor cells through passive targeting by EPR effect.And Ce6@PTP/DP micelles have good performance in generating ROS both in solution and in He La cells under light,and the generated ROS further triggers the breakage of TK bond,the generated ROS can further trigger the breakage of TK bond on the basis of providing PDT treatment.In the cytotoxicity experiment,the cytotoxicity of Ce6@PTP/DP（+）was found to be significantly stronger than that of the single chemotherapy and single PDT.Therefore,Ce6@PTP/DP micelles exhibited excellent cascading synergistic therapeutic effects during the treatment process.In order to overcome the aggregation-caused quenching effect（ACQ effect）of traditional photosensitizers,which greatly hinders the application of PDT in practical therapeutic applications,a light-controlled polymeric precursor delivery system with aggregation-induced emission（AIE）performance was constructed.The delivery system utilizes a click reaction to synthesize a polymeric precursor PEG-DBCO-PTX with an internal ROS-sensitive TK bond designed for efficient and controlled release of PTX,and AIEgen photosensitizer Y6 is loaded into its hydrophobic core to obtain Y6@PDP/DP micelles.The photosensitizer Y6 with excellent AIE performance allows this delivery system to compensate for the shortcomings of conventional photosensitizer ACQ effect.The AIE performance of this photosensitizer is superior,and the fluorescence signal of Y6@PDP/DP micelles has almost no decay after bleaching or scanning 200 times for cell samples incubated with Y6@PDP/DP micelles,which still have good photostability after loading into the polymer prodrug to form micelles.In vivo,Y6@PDP/DP nanoparticles with suitable particle size can be passively targeted and enriched through EPR effect when the intravenous circulation reached to the tumor site.Under specific wavelength light,Y6@PDP/DP can generate a large amount of ROS,which can realize photodynamic therapy on the one hand,and prompt the breakage of TK bond,the ROS-sensitive bond in the prodrug of the nanodrug delivery system on the other hand,thus releasing PTX,effectively realizing the combined PDT/chemotherapy treatment.Compared with the single chemotherapy or photodynamic therapy,the tumors of mice injected with the nanodrug delivery system Y6@PDP/DP and treated with light were significantly suppressed and the therapeutic effect was significantly enhanced.In addition,imaging and tissue sections from various organs showed that the micelles caused very little damage to various other organs in vivo.This polymer prodrug system well addresses the ACQ effect of conventional photosensitizers through the introduction of AIE photosensitizers,and in addition achieves the synergistic treatment effect of PDT/chemotherapy combination enhancement.