Manganese-doping Titanium Disulfide Nanosheets For Cancer Sequential Gas-sonodynamic Strategy With Immune Checkpoint Blockade Therapy

Sonodynamic therapy(SDT)is a novel therapeutic strategy that utilizes ultrasound(US)with sonosensitizers to induce a large amount of reactive oxygen species(ROS)to kill malignant tumors.Compared to the well-known photodynamic therapy(PDT),SDT features excellent tissue-penetration depth and controllability.In recent years,titanium(Ti)-based nanomaterials have gradually become one of the research focuses of SDT due to their outstanding sonodynamic effects and high safety.Unfortunately,SDT alone only generates limited ROS,which is not sufficient to trigger robust immunogenic cell death(ICD)and subsequent immune responses on many occasions.In addition,SDT might affect therapeutic performance and result in immune tolerance,even resulting in recurrence and metastasis.On the other hand,gas therapy(GT)can modulate tumor metabolism as well as the microenvironment,thereby receiving increasing attention.How to combine gas and SDT efficiently is meaningful to some extent.Based on this,in this thesis,polyethylene glycol(PEG)-modified manganese(Mn)-doped titanium disulfide nanosheets(PEG-Mn:TiSx NSs,abbreviated as MnTiS-PEG)are synthesized and served as a kind of cascade bioreactor for sequential GT-enhanced SDT,and are combined with immune checkpoint blocking(ICB)for cancer therapy.The main research results are summarized as follows:Chapter 1:A summary of the advantages and recent development of Ti-based sonosensitizers for SDT,including the synthesis and modification of Ti-based sonosensitizers,Ti-based sonosensitizer-mediated enhanced SDT strategy,progress in combination with other therapies,and the toxicity of Ti-based sonosensitizers.Finally,the topic basis and research content of this paper are introduced.Chapter 2:Development of a new H2S-generating TiS2 multifunctional nanomaterials.A novel type of Ti-based sonosensitizers,MnTiS,is synthesized via a hightemperature oil phase approach and modified with DSPE-PEG(MnTiS-PEG)for sequential GT-enhanced SDT.First,the synthesis and modification of MnTiS-PEG are successfully demonstrated by relevant characterization methods.Due to the abundant sulfur content,MnTiS-PEG synthesized by this method can first generate a large amount of H2S gas.After degradation,the ability of ROS generation of such nanosheets under US treatment is greatly improved by the enhanced vacancy structures,which is superior to that of commercial TiO2 nanoparticles.At the same time,the nanosheets can release Mn2+within a short time.MnTiS-PEG features a good prospect.Based on this,we hope to design an appropriate therapeutic strategy for cancer therapy and even other biomedical applications of such multifunctional nanoplatforms.Chapter 3:Development of sequential GT-SDT for cancer immunotherapy based on MnTiS-PEG.MnTiS-PEG will first release a large amount of H2S,which will not only cause mitochondrial damage in cells but also form defective oxidation structures.Under subsequent US treatment,the sonodynamic effect is greatly enhanced,further killing tumor cells.Meanwhile,the accompanying release of Mn2+ during the degradation will promote the maturation of dendric cells(DCs)and further enhance the immune response.In vitro data showed that this cascade process has a good cell-killing effect and a satisfactory ICD activation effect.Furthermore,sequential GT-SDT significantly inhibited the growth of CT26 colon cancer tumors in vivo and enhanced DCs maturation and cytotoxic T lymphocytes(CTLs)infiltration.However,this sequential strategy can induce immune tolerance to some extent.Therefore,ICB therapy is combined to further reverse the "cold" tumors into the "hot" tumors by modulating the immune environment.Such a strategy can inhibit not only tumors treated directly with GT-SDT but also untreated distant tumors,providing a possible way to promote the combination of SDT and immunotherapy.In this thesis,we successfully synthesized a novel Ti-based material,MnTiS-PEG,and proposed a cancer sequential treatment strategy for GT-SDT according to its properties.Specifically,MnTiS-PEG can generate H2S that induces cell apoptosis.Owing to the vacancy structure of TiO2 induced by H2S release,the sonodynamic effect of the degraded materials is boosted,which will kill tumor cells further.The released Mn2+ can promote DCs maturation.At the same time,ICB is combined to modulate the immune microenvironment to boost tumor treatment.This work explores and expands the application of Ti-based materials in sonodynamic-immune therapy,providing a certain idea for non-invasive tumor therapy.