Hybrid Chalcogen Bonds Bridged Dimeric Prodrug Nanoassemblies For Cancer Therapy

The construction of antitumor drug delivery system with high efficiency and low toxicity is currently a hot topic in cancer therapy research.Small molecule prodrug selfassembly nanotechnology,which combines the dual advantages of prodrugs and nanodrugs,has become an important platform for antitumor drug delivery.The strategy is to couple the drugs with flexible "modified chains" to balance the inter-molecular forces,thus endowing the drugs with the ability to form nanostructures by self-assembly in aqueous solution.As the main body of the nanostructure,the prodrug avoids the use of carrier materials and has the advantages of high drug loading.self-delivery and responsive drug release.The prodrug self-assembly nanoparticles not only overcome the problems of rapid metabolism and poor targeting of small molecular prodrugs,but also avoid the toxicity caused by the large use of carrier materials.By coupling two drug molecules with a suitable linker,the developed homodimeric prodrug could self-assemble into nanoparticles(NPs)without the carriers.The drug loading of the homodimeric prodrug nanoparticles(HPNPs)can be further increased to about 70%,which has important scientific significance and application value.However.two key factors restrict the application of HPNPs:poor self-assembling capability and unsatisfactory on-demand target site-bioactivation.The rational design of HPNPs with good self-assembly stability and tumor-selective bioactivation is still a great challenge.In our previous studies,Sulfur bonds,especially trisulfide bond,have been found to ameliorate the self-assembly stability of HPNPs and could trigger the super reductionresponsive release of active drugs.However,the intracellular microenvironment of tumor cells is characterized by the heterogeneous redox state due to the irregular production of glutathione(GSH)and reactive oxygen species(ROS).The antitumor efficacy of HPNPs with single reduction-responsivity may be restricted due to the heterogeneous tumor redox microenvironment,thereby prodrugs bioactivated by multistimuli of the tumor microenvironment are quite required.Sulfur,selenium and tellurium belong to chalcogen.Recent studies show that selenium bond can enhance the self-assembly ability of prodrug more effectively and has higher oxidation sensitivity than sulfur bond.However,the role of tellurium bond in driving the self-assembly of prodrug and triggering the activation of prodrug response remains to be explored.Inspired by the physicochemical property of chalcogen,we replaced the middle sulfur atom of the trisulfide bond with a tellurium atom or selenium atom to construct novel redox dual-responsive-STeS-and-SSeS-hybrid chalcogen bonds.The hybrid chalcogen bond is expected to realize stable assembly and intelligent activation in a tumor redox heterogeneous microenvironmentIn this study,the hybrid chalcogen bonds(-STeS-and-SSeS-)bridged HPNPs were developed using docetaxel(DTX)as the model drug.In addition,-SSS-and-SCSbridged prodrugs were also synthesized as control.The effects of hybrid chalcogen bonds on the self-assembly,bioactivation,pharmacokinetic behavior,biodistribution,and pharmacodynamics of HPNPs were investigated in detail.Furthermore,molecular dynamics simulation and bioactive intermediates were investigated to illustrate the assembly mechanism.We found that all the four designed dimer prodrugs could spontaneously form uniform and stable nanoparticles in water.Compared with theSSS-and-SCS-bonds,the hybrid chalcogen bonds effectively improved the selfassembly stability of the dimer prodrug by providing strong intermolecular force and sufficient steric hindrance.The assembly capacity of-STeS-bridged dimer prodrug is the strongest because of the bond angle closest to 90° and stronger chalcogen bond interaction.We investigated the redox-responsivity of HPNPs and analyzed the mechanism.It was found that We found that the introduction of tellurium atoms or selenium atoms changed the distribution of electron clouds of bonding bonds and provided redox dual reaction sites.Tellurium atom had the strongest electron donor effect,so the electron cloud density of sulfur atom in-STeS-bond was higher(oxidation reaction site),and the electron cloud density of tellurium atom was lower(reduction reaction site).Therefore,the-STeS-bridged HPNPs exhibit the strongest oxidation and reduction dual responsiveness.We evaluated the cytotoxicity,cellular uptake and intracellular drug release of dimer prodrug self-assembled nanoparticles.The HPNPs had similar cell uptake efficiency.Because of its stronger redox response,-STeS-bridged HPNPs released docetaxel faster in tumor intracellular environment,resulting in more effective tumor cell killing.In addition,we also studied the ability of HPNPs to induce apoptosis(43.15%)and tubulin inhibition in tumor cells,and investigated its influence on intracellular redox microenvironment.We studied the fate in vivo and the antitumor effects of HPNPs.The-STeS-/-SSeS/-SSS-/-SCS-bridged HPNPs significantly increased the area under the blood concentration-time curve of docetaxel by 37.50,36.52,33.39 and 127.74 times compared with the docetaxel solution and efficiently accumulated in tumor tissues.The-STeS-bridged HPNPs responded to the heterogeneous tumor microenvironment more effectively,resulting in the efficient and selective DTX release,which had the optimal anti-tumor effect and reduced the side effects of docetaxel on normal tissues.In this study,the molecular mechanism of self-assembly,intelligent response and improvement of drug efficacy driven by hybrid chalcogen bonds was deeply explored.The application potential of chalcogenides in the construction of prodrug nanoparticles is analyzed,which enriches the design theory of prodrug nanoparticles.This will hopefully solve the two bottleneck problems that restrict the dimer prodrug nanoparticles,and provide a new strategy for developing a high-efficiency and lowtoxicity antitumor drug delivery system.