Design Of Redox-responsive Polyprodrugs Nanomedicine For Tumor Therapy

Chemotherapy as a traditional antitumor strategy has been developed in clinical application.However,its poor selectivity and serious side effects seriously affect their application in treatment.Prodrugs are bioreversible derivatives of drug molecules that undergo an enzymatic or chemical transformation in vivo to release the active parent drug,which can then exert the desired pharmacological effect and make develop tumor-specific prodrugs important.Compared with traditional nanomedicine,polyprodrug nanomedicine not only possesses the advantages of high drug loading,stability and structural controllability of polyprodrug,but also good water solubility and tumor targeting properties of nanomedicine,which has attracted widespread attention.In addition,high intracellular glutathione（GSH）is critical for maintaining cell function and ensuring cell survival.Also,the growing intracellular reactive oxygen species（ROS）can break down redox homeostasis in tumor cells,which further promotes apoptosis.Therefore,it is great significance to develop redox-responsive polyprodrugs which can modulate redox homeostasis in tumor cells for improving the efficacy of chemotherapy.Herein,we developed three redox-responsive polyprodrug nanosystems which can break out the redox homeostasis in tumor cells for drug resistance reversal and drug activation enhancement.1.High intracellular GSH levels play an important role in multidrug resistance（MDR）in cancer cells.Polymer with high disulfide density depletes intracellular antioxidant GSH via the disulfide-thiol exchange reaction to disrupt intracellular redox homeostasis in cells.Therefore,we designed a polyprodrug（denoted as PSSD）based on poly（disulfide）with a high disulfide density which can be used as a GSH scavenger to reverse MDR as well as a prodrug backbone to target high intracellular GSH levels in cancer cells,providing a general strategy for drug resistance reversal.The amphiphilic polyprodrug can self-assemble into nanoparticles with proper size,high drug loading efficiency and a sharp response to GSH,thereby delivering DOX to cancer cells.The poly（disulfide）backbone with a high disulfide density depletes intracellular antioxidant GSH via the disulfide-thiol exchange reaction to disrupt intracellular redox homeostasis in MDR cells.Simultaneously,DOX can be activated through a cascade reaction,and the degradation of the poly（disulfide）backbone further facilitates its drug release.Decreased intracellular GSH content can cause an increase in ROS level and down-regulate the expression of P-glycoprotein（P-gp）,which further reduce the efflux of intracellular DOX for DOX resistance reversal.2.Tumor-associated enzyme-activated prodrugs have received numerous attention due to the high selectivity of enzymes overexpressed in cancer cells.However,use of enzyme-activated prodrug is limited by ineffective drug activation owing to the paucity of tumor-associated enzymes which represent an essential step for the functioning of the prodrug.Recently the ability of cancer cells to overproduce ROS to develop ROS-responsive drug delivery systems have been exploited,however,intracellular concentration of ROS is still not high enough for efficient drug activation,which represents an important intrinsic limitation for the ROS-responsive systems despite their great potential.Therefore,development of new strategies for enzyme-activated ROS generation are imperative to improvement of tumor selectivity.The generated ROS can be further utilized for efficient prodrug activation.In the present study,we developed a tumor-selective cascade amplified prodrug activation systems(denoted PTK_DOX/Cy)consisting of cancer cells overexpressed cathepsin B（CTB）-activated Cy NH₂ prodrug（Cy NH-Citval）and ROS-responsive polyprodrug(PTK_DOX)of doxorubicin（DOX）conjugated on the side chain of poly（thioketal）.Upon interacting with overexpressed cathepsin B in cancer cells,Cy NH₂ can be activated to restore toxicity,and NIR fluorescence turn on for drug activation monitoring.Activated Cy NH₂ can lead to mitochondrial dysfunction in cancer cells,thereby elevating levels of intracellular ROS.Consequently,high ROS levels mediate activation of the polyprodrug PTK_DOX,thereby activating a cascade and amplifying DOX prodrug activation.More importantly,Cy NH₂ and DOX showed synergistic oxidation and chemotherapy.3.In view of the low level of stimuli-responsive signals in the tumor microenvironment,the design of traditional prodrug is limited by ineffective drug activation owing to a stimuli-responsive molecule can only activate one prodrug molecule.Therefore,development of polyprodrug nanomedicine with response signal amplification are imperative to overcome the limitations of traditional prodrugs such as ineffective drug activation and incomplete drug release.Self-immolative polymers with amplified stimuli-responsive signal are distinctive materials able to disassemble in a domino-like mechanism from head-to-tail upon a triggering event induced by an external stimulus,which have attracted widespread attention.Herein,we developed a tumor-selective polyprodrug nanomedicine with self-amplified prodrug activation（denoted SIPN）consisting of cancer cells overexpressed NAD（P）H:quinone oxidoreductase 1（NQO1）-activated Cy NH₂ prodrug（NCy）and ROS-responsive polyprodrug（SIP-DOX）of doxorubicin（DOX）conjugated on the side chain of self-immolative polymers.Upon interacting with overexpressed ROS in cancer cells,self-immolative polymers can be disassembled with multi-molecular DOX activated and NCy released in a domino-like mechanism through multiple quinone-methide eliminations and decarboxylation sequence,which initially accomplish the amplification of ROS-responsive signal amplification.After interacting with overexpressed NQO1,Cy NH₂ can be activated from NCy with NIR fluorescence turn on.Then activated Cy NH₂ can lead to mitochondrial dysfunction in cancer cells,thereby elevating the levels of intracellular ROS.Consequently,high ROS levels mediate activation of the polyprodrug SIP-DOX with more DOX released,thereby achieving self-amplified prodrug activation.