The Construction Of Redox Dynamically Controlled Polymeric Prodrug Nanogels And Applications In Antitumor Therapy

Reactive oxygen species(ROS)and antioxidant systems are important for cells to maintain redox homeostasis and perform normal physiological activities,and cancer cells produce large amounts of ROS to support their rapid development.Excessive levels of ROS,however,can cause damage to deoxyribonucleic acid(DNA),proteins and lipids,ultimately triggering cell death,a phenomenon also known as oxidative stress.In order to resist damage caused by oxidative stress,the level of antioxidant system can scavenge ROS correspondingly up-regulated.In the antioxidant system,GSH,a major antioxidant,is a tripeptide composed of glutamic acid,cysteine,and glycine.Most intracellular GSH exists in a reduced form,which can react with oxidative substances such as ROS and be oxidized to glutathione disulfide(GSSG).The concentration of GSH in cancer cells is about 2-10 mM,i.e.about 1000-fold higher(2-10 μM)in the extracellular environment.This GSH concentration gradient has been used in various redox-responsive drug delivery systems to activate drugs in cancer cells.The intracellular redox state is in a state of homeostasis,and depletion of GSH will disrupt redox homeostasis and lead to ROS accumulation,ultimately triggering cellular dysfunction and death.The delivery of exogenous compounds or materials to cancerous tissue produces large amounts of reactive oxygen species and triggers cell death upon stimulation of light,ultrasound or chemical reactions.Although this ROS-based therapy has been applied clinically,the cellular antioxidant system scavenges reactive oxygen species,especially glutathione.It has been reported that reducing glutathione levels in tumor cells increases ROS levels and improves the efficacy of ROS-based therapy.In this dissertation,starting from the construction of redox dynamic regulated polymer prodrug nanogels,a variety of redox responses were designed and constructed for the purpose of enhancing tumor recognition and breaking redox homeostasis in tumor cells to improve the therapeutic effect of drugs.Type polymer prodrug nanogels are used in cancer chemotherapy,photodynamic therapy and immunotherapy.The specific contents are as follows:(1)Actively targeted redox-responsive mannosylated 10-hydroxycamptothecin(HCPT)prodrug nanocolloids were designed and prepared by a facile and versatile covalent cross-linking method,in which HCPT was combined with mannose(MAN)Conjugated to form HM NCs with disulfide bonds,the hydrophilic polymer PEG was surface-modified to increase stability and prolong cycling.HM NCs exhibited excellent tumor recognition and tumor accumulation due to the EPR effect and active tumor targeting of mannose.Meanwhile,mannose receptor(MR)-mediated endocytosis promoted the cellular internalization of HM NCs.Furthermore,high GSH levels in tumor cells can trigger the cleavage of disulfide bonds in HM NCs and release the loaded HCPT to target the ribozyme topoisomerase I(Top I)to induce DNA damage,while the released MAN leads to chemical Enhanced sensitivity,ultimately achieving enhanced chemotherapeutic effect.It was confirmed that HM NCs significantly inhibited tumor growth and significantly prolonged mouse survival both in vitro and in vivo,while exhibiting excellent biocompatibility.This novel design strategy facilitates the development of novel prodrug nanocolloids for drug delivery systems and is expected to provide more options for future clinical translation.(2)Singlet oxygen stimuli-responsive nanogels(BPNG)were designed and prepared by a facile and versatile covalent cross-linking method.The glutathione scavenger butthionine-sulfoximine(BSO)is combined with a crosslinker with vinyl disulfide.At the same time,the photosensitizer violetin(P18)was loaded.The surface of the nanogel is modified with the hydrophilic polymer PEG.Due to the EPR effect,the intravenously injected nanogel BPNG was enriched at the tumor site and was phagocytosed by tumor cells.Due to the high level of reactive oxygen species(ROS)content within tumor cells,a small amount of cleavage of the double bond of vinyl disulfide in BPNG releases free BSO and P18.At this time,660 nm laser irradiation was performed on the tumor part,and the photosensitizer P18 produced singlet oxygen,which further aggravated the breakage of the double bond and completely released more P18 and BSO from BPNG.A large amount of free P18 photodynamically generates more reactive oxygen species,resulting in immunogenic cell death(ICD)of tumor cells.At the same time,CRT was exposed on the cell surface to induce dendritic cell maturation.The released free BSO can bind to -glutathionyl cysteine synthase(-GCS).Since -GCS is an important rate-limiting enzyme for GSH synthesis,a large amount of BSO release reduces GSH levels in tumor cells.The increase of ROS level and the decrease of GSH level in tumor cells broke the original redox balance,which further caused oxidative stress in tumor cells.This singlet oxygen-responsive nanogel can effectively enhance the effects of photodynamic therapy and immunotherapy,significantly prolong the survival period of mice,and has broad application prospects.