Reduction-Responsive Doxorubicin Dimeric Prodrug Nanoparticles For Cancer Therapy

Cancer is a serious threat to human life and a major public health problem in the world.Chemotherapy is an important mean of cancer treatment.However,current chemotherapeutics generally suffer a lot from inefficient drug delivery,resulting in limited antitumor efficacy and serious side effects.In response to these problems,prodrug-based nanoparticles(NPs)have been developed,integrating the advantages of both prodrug strategies and nanocarriers.Compared with the traditional nanomedicines,dimeric prodrug nanoassemblies exhibit distinct high drug loading and low excipient-related toxicity because the prodrugs act as both the carriers and the cargos.However,the strong intermolecular forces between dimer prodrugs often limit their self-assembly ability,and how to design self-assembling prodrugs with good self-assembly properties is still a huge challenge.Our previous studies demonstrated that disulfide bond has a nearly vertical dihedral angle,which play an essential role in improving structural flexibility and balancing intermolecular forces during molecule self-assembly.Compared with the disulfide bond,the trisulfide bond has three sulfur atoms and two sulfur-containing dihedral angles,which perhaps further facilitate the self-assembly of dimeric prodrugs.Ideally,we hope that the prodrug nanoassemblies can remain intact in the systemic circulation and normal cells while intelligently releasing the active parent drugs in tumor cells.It has been reported that the concentration of glutathione(GSH)in tumor cells is over 1000-fold higher than in blood and much higher than that in normal cells.In response to the overexpressed GSH in tumor cells,the disulfide bond has been widely used as the "golden standard" to design redox-responsive systems.Compared with the disulfide bond,the trisulfide bond might be more sensitive to GSH because it has three redox reaction sites and higher redox potential.Therefore,we expect the trisulfide bond to be a reduction-supersensitive linkage with ultrahigh tumor selectivity.On the basis of the above considerations,we attempted to explore the impact of the trisulfide bond on the homodimeric prodrug nanoassemblies.Three homodimeric DOX prodrugs were synthesized using a thioether bond,disulfide bond,or trisulfide bond as linkages.Simple insertion of a trisulfide bond could transform the DOX homodimeric prodrug into a uniform nanostructure with three highlights:high drug loading(67.24%,w/w),high self-assembly stability,and high tumor selectivity.Compared with the disulfide bond and thioether bond,the trisulfide bond significantly promoted the self-assembly of DOX homodimeric prodrugs,thereby improving the colloidal stability,pharmacokinetics,and tumor accumulation of prodrug nanoassemblies.Furthermore,the trisulfide bond showed higher GSH sensitivity than disulfide bond,and the triggering mechanism was also elucidated in detail.As a result,trisulfide bond-bridged prodrug nanoassemblies exhibited highly selective cytotoxicity on tumor cells as opposed to normal cells,significantly reducing the systemic toxicity of DOX.Despite its excellent redox-responsiveness and improved assembly ability,trisulfide bond-bridged DOX dimeric prodrug nanoassemblies still seriously suffer from rapid blood clearance.To improve the delivery efficiency and stability,prodrugs with special structure are capable to be loaded into liposome interior.By leveraging the coordination effect between DOX and Fe3+,trisulfide bond-bridged DOX dimeric prodrug was actively loaded into the core of the unsaturated lipids-rich liposome via iron ion gradient method.First,Fe3+could react with the overexpressed GSH in tumor cells,inducing the GSH depletion and Fe2+generation.Second,the cleavage of trisulfide bond could also consume GSH,and the released DOX further produces H2O2,which would react with the generated Fe2+ in step one to induce efficient Fenton reaction-dependent ferroptosis.Third,the formed Fe3+/Fe2+couple could directly catalyze peroxidation of unsaturated lipids to boost Fenton reaction-independent ferroptosis.This iron-prodrug liposome nanoreactor precisely programs multimodal ferroptosis by integrating GSH depletion,ROS generation and lipid peroxidation,providing new sights for efficient cancer therapy.