A ROS-responsive hydrogel incorporated with dental follicle stem cell-derived small extracellular vesicles promotes dental pulp repair by ameliorating oxidative stress

Pulpitis,an inflammatory disease of dental pulp tissues,ultimately results in the loss of pulp defense properties.Existing clinical modalities cannot effectively promote inflamed pulp repair.Oxidative stress is a major obstacle inhibiting pulp repair.Due to their powerful antioxidative capacity,mesenchymal stem cell-derived small extracellular vesicles(MSC-sEVs)exhibit potential for treating oxidative stress-related disorders.However,whether MSC-sEVs shield dental pulp tissues from oxidative damage is largely unknown.Here,we showed that dental follicle stem cell-derived sEVs(DFSC-sEVs)have antioxidative and prohealing effects on a rat LPS-induced pulpitis model by enhancing the survival,proliferation and odontogenesis of H_(2)O_(2)-injured dental pulp stem cells(DPSCs).Additionally,DFSC-sEVs restored the oxidative/antioxidative balance in DPSC mitochondria and had comparable effects on ameliorating mitochondrial dysfunction with the mitochondrion-targeted antioxidant Mito-Tempo.To improve the efficacy of DFSC-sEVs,we fabricated an intelligent and injectable hydrogel to release DFSC-sEVs by combining sodium alginate(SA)and the ROS sensor RhB-AC.The newly formed SA-RhB hydrogel efficiently encapsulates DFSC-sEVs and exhibits controlled release of DFSC-sEVs in a HClO/ClO^(-)concentration-dependent manner,providing a synergistic antioxidant effect with DFSC-sEVs.These results suggest that DFSC-sEVs-loaded SA-RhB is a promising minimally invasive treatment for pulpitis by enhancing tissue repair in the pulp wound microenvironment.

ROS-responsive nanoparticle delivery of ferroptosis inhibitor prodrug to facilitate mesenchymal stem cell-mediated spinal cord injury repair

Spinal cord injury(SCI)is a traumatic condition that results in impaired motor and sensory function.Ferroptosis is one of the main causes of neural cell death and loss of neurological function in the spinal cord,and ferroptosis inhibitors are effective in reducing inflammation and repairing SCI.Although human umbilical cord mesenchymal stem cells(Huc-MSCs)can ameliorate inflammatory microenvironments and promote neural regeneration in SCI,their efficacy is greatly limited by the local microenvironment after SCI.Therefore,in this study,we constructed a drug-release nanoparticle system with synergistic Huc-MSCs and ferroptosis inhibitor,in which we anchored Huc-MSCs by a Tz-A6 peptide based on the CD44-targeting sequence,and combined with the reactive oxygen species(ROS)-responsive drug nanocarrier mPEG-b-Lys-BECI-TCO at the other end for SCI repair.Meanwhile,we also modified the classic ferroptosis inhibitor Ferrostatin-1(Fer-1)and synthesized a new prodrug Feborastatin-1(Feb-1).The results showed that this treatment regimen significantly inhibited the ferroptosis and inflammatory response after SCI,and promoted the recovery of neurological function in rats with SCI.This study developed a combination therapy for the treatment of SCI and also provides a new strategy for the construction of a drug-coordinated cell therapy system.

Mitochondrial-targeted and ROS-responsive nanocarrier via nose-to-brain pathway for ischemic stroke treatment

Oxidative stress injury and mitochondrial dysfunction are major obstacles to neurological functional recovery after ischemic stroke.The development of new approaches to simultaneously diminish oxidative stress and resist mitochondrial dysfunction is urgently needed.Inspired by the overproduced reactive oxygen species(ROS)at ischemic neuron mitochondria,multifunctional nanoparticles with ROS-responsiveness and mitochondrial-targeted(SPNPs)were engineered,achieving specific targeting delivery and controllable drug release at ischemic penumbra.Due to the nose-to-brain pathway.SPNPs which were encapsulated in a thermo-sensitive gel by intranasal administration were directly delivered to the ischemic penumbra bypassing the blood-brain barrier(BBB)and enhancing delivery efficiency.The potential of SPNPs for ischemic stroke treatment was systematically evaluated in vitro and in rat models of middle cerebral artery occlusion(MCAO).Results demonstrated the mitochondrialtargeted and protective effects of SPNPs on H2O2-induced oxidative damage in SH-SY5Y cells.In vivo distribution analyzed by fuorescence imaging proved the rapid and enhanced active targeting of SPNPs to the ischemic area in MCAO rats.SPNPs by intranasal administration exhibited superior therapeutic efficacy by alleviating oxidative stress,diminishing infammation,repairing mitochondrial function,and decreasing apoptosis.This strategy provided a multifunctional delivery system for the effective treatment of ischemic injury,which also implies a potential application prospect for other central nervous diseases.

Targeting self-enhanced ROS-responsive artesunatum prodrug nanoassembly potentiates gemcitabine activity by down-regulating CDA expression in cervical cancer

Prodrug self-delivery carriers with targeting that specifically responded to tumor microenvironments have good potential to improve the application dilemma of approved clinical therapeutic drugs(systemic distribution and side effects).It's noted the conversion of gemcitabine(GEM)to inactive ingredients under the action of cytidine deaminase(CDA)during metabolism in vivo limits its clinical effect.A high level of reactive oxygen species(ROS)results in a high level of oxidative stress in tumor cells,which changes the expression of CDA and optimizes the metabolism of GEM in vivo and overcome drug resistance.In this study,the ROS responsive and ROS self-supplied prodrug of artemisia(ART)-thioacetal bond(TK)-GEM was synthesized and self-vectors based on ART-TK-GEM(TK@FA NPs)was prepared by using nano precipitation.ROS responsive characteristics ensure specific release of prodrugs in tumor cells with high level of ROS thereby reducing side effects on normal cells and tissues.The endogenous ROS and newly generated ROS by ART can reduce the expression of CDA and optimizes the metabolism of GEM,and the accumulated ROS can also induce apoptosis of tumor cells,realizing synergistic anti-tumor effect of chemical drugs and traditional Chinese medicines.This paper proposes a simple method by using clinically approved drugs to improve the insufficient effect of existing chemotherapy and overcome resistance,which has potential to appropriately shorten the drug development cycle and accelerate the clinical investigation of drugs.

ROS-responsive cyclodextrin nanoplatform for combined photodynamic therapy and chemotherapy of cancer

Cyclodextrin(CD) has special spatial structure and well biological safety,so it has been widely used for constructing CD-based na noplatforms.Through functionalization,cyclodextrin can form various stimulusresponse nanoplatforms,such as pH,temperature,redox,light and magnetic fields.In this study,we designed a highly sensitive reactive oxygen species(ROS)-responsive polymer PCP which encapsulated doxorubicin(DOX) and purpurin 18(P18) to achieve the syne rgy of photodynamic and chemotherapy.The high content of reactive oxygen species(ROS) in the tumor microenvironment(TME) triggers the cleavage of the borate bond of MPEG-CD-PHB(PCP),thereby promoting the re lease of drugs.When irradiated with nea rinfrared laser,the photosensitizer P18 released by polymer micelles can produce reactive oxygen species to promote cell apoptosis.Compared with monotherapy,a series of experiments confirmed that our micelles had enhanced anti-cancer activity.This work was beneficial to the design of ROS-responsive materials and provides an effective strategy for the application of collaborative anti-tumor therapy.

ROS-responsive biomimetic nanoparticles for potential application in targeted anti-atherosclerosis

The development of nanomedicines provides new opportunities for the treatment of atherosclerosis(AS)due to their great advantages such as the improved drug solubility,enhanced bioavailability and reduced side effects.Despite these advantages,nanomedicines are still facing some challenges.The problems remain in the short circulation life,lack of specific targeting and poor drug release controllability.In order to overcome the shortages of conventional nanomedicines,the combination of biomimetic strategy with smart nanoagents has been proposed.In light with the high reactive oxygen species(ROS)level in AS microenvironment and the fact that macrophages play a critical role in the pathogenesis of AS,we fabricated ROS-responsive biomimetic nanoparticles(NPs),which camouflaged macrophage membrane(MM)on ROS-responsive NPs loaded with rapamycin(RNPs)for potential application in AS therapy.The resulting ROSresponsive biomimetic NPs(MM/RNPs)exhibited favorable hydrodynamic size with negative surface charge,retained the functional proteins from MM,and showed ROS-responsive drug release.Because of the biomimetic camouflaging on surface,MM/RNPs could effectively escape from macrophages uptake and target to inflammatory endothelial cells.Meanwhile,MM/RNPs could inhibit the proliferation of macrophages and smooth muscle cells in vitro.Furthermore,the MM-coated NPs were found to be nontoxic in both cytotoxicity assay and in vivo toxicity evaluation.Consequently,these results demonstrated that MM/RNPs could be a potential candidate of drug delivery system for safe and effective anti-AS applications.

Regulation of pathological BBB restoration via nanostructured ROS-responsive glycolipid-like copolymer entrapping siVEGF for glioblastoma targeted therapeutics

Glioblastoma(GBM)is one of the malignant brain tumors with high mortality and no curative treatments.Abnormally elevated vascular endothelial growth factor(VEGF)in GBM seriously disrupts the blood brain barrier(BBB)with an increased permeability,resulting in poor outcome and prognosis.RNAi interference has shown strong potential to inhibit VEGF expression,thus it is necessary to development an effective and safe gene delivery system possessing the ability to cross the BBB and target GBM cells.This study aims to explore the anti-GBM effect of angiopep-2(Ap)peptide modified reactive oxygen species(ROS)cleavable thioketal(TK)linked glycolipid-like nanocarrier(CSTKSA)delivering anti-VEGF siRNA(R),termed as Ap-CSTKSA/R complexes.Ap functionalized modification produced an enhanced cellular uptake and a stronger bio-distribution of Ap-CSTKSA/R complexes in U87 MG cells and brain tumor tissues,respectively.Ap-CSTKSA/R complexes exhibited great superiority in GBM growth inhibition and finally translated into the longest survival period mainly via receptor-mediated targeting delivery,VEGF gene silencing accompanied with remarkable angiogenesis inhibition,and suppressed expression of caveolin-1 which is involved in BBB functional regulation in the occurrence and treatment of GBM.The study indicated that Ap functionalization on ROS-responsive glycolipid-like copolymer exhibits a promising and effective gene delivery platform for GBM targeted treatment.

Synthesis of polypeptide bearing 1,4-dithiane pendants for ROS-responsive drug release

Stimuli-re sponsive polypeptides have been intensively investigated fo r controlled drug release,owing to their favorable biocompatibility and biodegradability.In this work,we designed and synthesized a new kind of polypeptide bearing 1,4-dithiane pendants for reactive oxygen species(ROS)-responsive drug release.The polypeptide-based block copolymer was facilely synthesized by ring-opening polymerization(ROP)of 1,4-dithian-substituted L-glutamate N-carboxyanhydride(DTG-NCA)monomer using an amino-terminated poly(ethylene glycol)methyl ether(mPEG-NH2)as the macro molecular initiator.The resulta nt block copolyme r,mPEG-b-PDTG,could self-assemble into unifo rm micelles in aqueous medium owing to its amphiphilic structure.Then,the H2 O2-triggered oxidation behaviors of the mPEG-b-PDTG micelles were studied by dynamic light scattering(DLS),FT-IR and turbidimetric assay.It was revealed that the oxidation of thioether into sulfoxide in the side chains would result in disassembly of the micelles.Furthermore,the ROS-responsive drug release behavior of the mPEG-b-PDTG micelles was verified by using Nile Red as a model drug.MTT assay also proved that mPEG-b-PDTG was non-toxic in B16 F10 and L929 cells.Therefore,such a new class of oxidation-responsive polypeptide might provide a promising platform for ROS-responsive drug delivery.

Modulating autophagic flux via ROS-responsive targeted micelles to restore neuronal proteostasis in Alzheimer’s disease

Compromised autophagy and defective lysosomal clearance significantly contribute to impaired neuronal proteostasis,which represents a hallmark of Alzheimer’s disease(AD)and other age-related neurodegenerative disorders.Growing evidence has implicated that modulating autophagic flux,instead of inducing autophagosome formation alone,would be more reliable to rescue neuronal proteostasis.Concurrently,selectively enhancing drug concentrations in the leision areas,instead of the whole brain,will maximize therapeutic efficacy while reduing non-selective autophagy induction.Herein,we design a ROS-responsive targeted micelle system(TT-NM/Rapa)to enhance the delivery efficiency of rapamycin to neurons in AD lesions guided by the fusion peptide TPL,and facilitate its intracellular release via ROS-mediated disassembly of micelles,thereby maximizing autophagic flux modulating efficacy of rapamycin in neurons.Consequently,it promotes the efficient clearance of intracellular neurotoxic proteins,β-amyloid and hyperphosphorylated tau proteins,and ameliorates memory defects and neuronal damage in 3×Tg-AD transgenic mice.Our studies demonstrate a promising strategy to restore autophagic flux and improve neuronal proteostasis by rationally-engineered nano-systems for delaying the progression of AD.

ROS-responsive thioether-containing hyperbranchede polymer micelles for light-triggered drug releas

As a kind of promising drug carriers,smart polymers have attracted much attention due to the effective and controlled drug release in target cells.Herein,a reactive oxygen species(ROS)-responsive thioether-containing amphiphilic hyperbranched polymer prepared from MTPA and TMPTGE(HBPMT)is synthesized from 3-(methylthio)propylamine(MTPA)and trimethylolpropane triglycidyl ether(TMPTGE)by the amine-epoxy click reaction via A2+B3 onepot approach.Benefiting from its inherent amphiphilic nature,HBPMT can selfassemble into stable micelles in water.Triggered by H_(2)O_(2),these micelles can be dissociated rapidly because hydrophobic thioether segments in their cores are oxidized into hydrophilic sulfoxide or sulfone groups.Additionally,the ROS produced by photosensitizer under light irradiation can also play the same role of H_(2)O_(2).Such HBPMT micelles can be utilized to encapsulate anticancer drug paclitaxel(PTX)and photosensitizer chlorin e6(Ce6)simultaneously for drug delivery and control release.The methyl thiazolyl tetrazolium assay toward MCF-7 tumor cells(a human breast adenocarcinoma cell line)indicates that these micelles encapsulated with PTX and Ce6 exhibit a significant combinational efficacy of cell proliferation inhibition,which means the promising potential for synergistic chemo-photodynamic cancer therapy.Such a novel nanocarrier based on amphiphilic to hydrophilic transition would provide a candidate for controlled drug release and cancer combination therapy.

Natural polysaccharide-based smart CXCR4-targeted nano-system for magnified liver fibrosis therapy

Activated hepatic stellate cells(aHSCs),the main source of extracellular matrix deposition,are key targets in liver fibrosis.However,no effective drug specific to aHSCs has been clinically applied due to poor drug delivery efficiency.Herein,we designed a CXC chemokine receptor 4(CXCR4)-targeted reactive oxygen species(ROS)-responsive platform AMD-Dex-ROS-responsive-sorafenib(ARS)based on natural polysaccharide and thioctic acid frame,which can deliver anti-fibrosis drug represented by sorafenib specifically to aHSCs on account of CXCR4 over-expression on aHSCs,and smartly disassemble via ROS-responsive thioketal rupture relying on high intracellular ROS in HSCs,realized on-demand drug release and effective liver fibrosis reversion.Notably,in this platform,the CXCR4 antagonist AMD3100 not only enhanced aHSCs targeting efficiency of sorafenib but also effectively magnified the aHSCs elimination of sorafenib by blocking stroma cell derived factor-1(SDF-1)/CXCR4-induced aHSCs protection,resulting in synergistic anti-fibrosis effect.The platform provided a new approach for drug delivery system design and liver fibrosis treatment.

IL-2-loaded Polypeptide Nanoparticles for Enhanced Anti-cancer Immunotherapy

Interleukin 2 (IL-2) is widely used as an active immunotherapeutic agent in clinical metastatic cancers. However, its therapeutic concentrations do not last long due to its short half-life. Thus, only a transient proliferation of the anti-cancer CD8+ T cells can be achieved, resulting in poor efficacy. Therefore, the aim of this work was to create a system that promotes CD8+ T cell proliferation at the tumor site using IL-2 persistently present and activates an anti-cancer immune response. This goal was achieved by the design of the IL-2-loaded polypeptide nanoparticles (P-IL-2) where methoxy poly(ethylene glycol) block poly-[(N-2-hydroxyethyl)-aspartamide] phenylboronic acid was used to encapsulate IL-2 through boron-nitrogen coordination with poly(L-lysine). P-IL-2 significantly prolonged the circulation time of IL-2 and achieved a selective drug release at the tumor site in the presence of high levels of reactive oxygen species, thus activating an anti-cancer immune response and exerting a better anti-cancer effect. The half-life of P-IL-2 was 3.15-fold higher than that of IL-2, and the quantity of CD8+ T cells after using P-IL-2 was 1.89-fold higher than that after using IL-2. In addition, the combination of P-IL-2 and anti-CTLA-4 monoclonal antibody resulted in an enhanced immune activation. Hence, this work provides a new approach to improve the efficacy of IL-2 in anti-cancer immunotherapy.

Stiffness-tuned and ROS-sensitive hydrogel incorporating complement C5a receptor antagonist modulates antibacterial activity of macrophages for periodontitis treatment

Periodontitis is admittedly a microbe-driven intractable infectious disease,in which Porphyromonas gingivalis(Pg)plays a keystone role.Pg can selectively impair the antimicrobial responses of periodontal resident macrophages including their phagocytic and bactericidal activity without interfering their proinflammatory activity,which leads to microflora disturbance,destructive periodontal inflammation and alveolar bone loss eventually.Here,an injectable ROS-sensitive hydrogel is developed for releasing active bone marrow-derived macrophages(named ex-situ macrophages hereafter)and a complement C5a receptor antagonist(C5A)to the gingival crevice.Through appropriately tuning the hydrogel stiffness,the phagocytic activity of these macrophages is greatly enhanced,reaching an optimal performance at the elastic modulus of 106 kPa.Meanwhile,C5A avoids undesired C5a receptor activation by Pg to ensure the bacterial killing activity of both the ex-situ and in-situ macrophages.Besides,the ROS-sensitive hydrogels show another distinct feature of decreasing the ROS level in periodontal niche,which contributes to the alleviated periodontal inflammation and attenuated bone loss as well.This study highlights the potential of utilizing hydrogels with tailored biomechanical properties to remodel the functions of therapeutic cells,which is expected to find wide applications even beyond periodontitis treatment.

A nanocleaner specifically penetrates the blood-brain barrier at lesions to clean toxic proteins and regulate inflammation in Alzheimer's disease

Insurmountable blood-brain barrier(BBB) and complex pathological features are the key factors affecting the treatment of Alzheimer's disease(AD).Poor accumulation of drugs in lesion sites and undesired effectiveness of simply reducing Aβ deposition or TAU protein need to be resolved urgently.Herein,a nanocleaner is designed with a rapamycin-loaded ROS-responsive PLGA core and surface modification with KLVFF peptide and acid-cleavable DAG peptide [R@(ox-PLGA)-KcD].DAG can enhance the targeting and internalization effect of nanocleaner towards neurovascular unit endothelial cells in AD lesions,and subsequently detach from nanocleaner in response to acidic microenvironment of endosomes to promote the transcytosis of nanocleaner from endothelial cells into brain parenchyma.Then exposed KLVFF can capture and carry Aβ to microglia,attenuating Aβ-induced neurotoxicity.Strikingly,rapamycin,an autophagy promoter,is rapidly liberated from nanocleaner in the high ROS level of lesions to improve Aβ degradation and normalize inflammatory condition.This design altogether accelerates Aβ degradation and alleviates oxidative stress and excessive inflammatory response.Collectively,our finding offers a strategy to target the AD lesions precisely and multi-pronged therapies for clearing the toxic proteins and modulating lesion microenvironment,to achieve efficient AD therapy.

Intelligent lesion blood–brain barrier targeting nano-missiles for Alzheimer's disease treatment by anti-neuroinflammation and neuroprotection

The treatment of Alzheimer's disease(AD)is one of the most difficult challenges in neurodegenerative diseases due to the insufficient blood‒brain barrier(BBB)permeability and unsatisfactory intra-brain distribution of drugs.Therefore,we established an ibuprofen and FK506 encapsulated drug co-delivery system(Ibu&FK@RNPs),which can target the receptor of advanced glycation endproducts(RAGE)and response to the high level of reactive oxygen species(ROS)in AD.RAGE is highly and specifically expressed on the lesion neurovascular unit of AD,this property helps to improve targeting specificity of the system and reduce unselective distribution in normal brain.Meanwhile,these two drugs can be specifically released in astrocytes of AD lesion in response to high levels of ROS.As a result,the cognition of AD mice was significantly improved and the quantity of Aβplaques was decreased.Neurotoxicity was also alleviated with structural regeneration and functional recovery of neurons.Besides,the neuroinflammation dominated by NF-κB pathway was significantly inhibited with decreased NF-κB and IL-1βin the brain.Overall,Ibu&FK@RNPs can efficiently and successively target diseased BBB and astrocytes in AD lesion.Thus it significantly enhances intracephalic accumulation of drugs and efficiently treats AD by anti-neuroinflammation and neuroprotection.

Co-delivery of photosensitizer and diclofenac through sequentially responsive bilirubin nanocarriers for combating hypoxic tumors

Considering that photodynamic therapy(PDT)-induced oxygen consumption and microvascular damage could exacerbate hypoxia to drive more glycolysis and angiogenesis, a novel approach to potentiate PDT and overcome the resistances of hypoxia is avidly needed. Herein, morpholine-modified PEGylated bilirubin was proposed to co-deliver chlorin e6, a photosensitizer, and diclofenac(Dc). In acidic milieu, the presence of morpholine could enable the nanocarriers to selectively accumulate in tumor cells, while PDT-generated reactive oxidative species(ROS) resulted in the collapse of bilirubin nanoparticles and rapid release of Dc. Combining with Dc showed a higher rate of apoptosis over PDT alone and simultaneously triggered a domino effect, including blocking the activity and expression of lactate dehydrogenase A(LDHA), interfering with lactate secretion, suppressing the activation of various angiogenic factors and thus obviating hypoxia-induced resistance-glycolysis and angiogenesis. In addition, inhibition of hypoxia-inducible factor-1a(HIF-1a) by Dc alleviated hypoxia-induced resistance. This study offered a sequentially responsive platform to achieve sufficient tumor enrichment, on-demand drug release and superior anti-tumor outcomes in vitro and in vivo.

Light-controllable charge-reversal nanoparticles with polyinosinic-polycytidylic acid for enhancing immunotherapy of triple negative breast cancer

Nucleic acid drugs are highly applicable for cancer immunotherapy with promising therapeutic effects, while targeting delivery of these drugs to disease lesions remains challenging. Cationic polymeric nanoparticles have paved the way for efficient delivery of nucleic acid drugs, and achieved stimuli-responsive disassembly in tumor microenvironment(TME). However, TME is highly heterogeneous between individuals, and most nanocarriers lack active-control over the release of loaded nucleic acid drugs, which will definitely reduce the therapeutic efficacy. Herein, we have developed a lightcontrollable charge-reversal nanoparticle(LCCN) with controlled release of polyinosinic-polycytidylic acid [Poly(I:C)] to treat triple negative breast cancer(TNBC) by enhanced photodynamic immunotherapy. The nanoparticles keep suitably positive charge for stable loading of Poly(I:C), while rapidly reverse to negative charge after near-infrared light irradiation to release Poly(I:C). LCCN-Poly(I:C) nanoparticles trigger effective phototoxicity and immunogenic cell death on 4 T1 tumor cells, elevate antitumor immune responses and inhibit the growth of primary and abscopal 4 T1 tumors in mice. The approach provides a promising strategy for controlled release of various nucleic acid-based immune modulators, which may enhance the efficacy of photodynamic immunotherapy against TNBC.

Robust and Tumor-Environment-Activated DNA Cross-Linker Driving Nanoparticle Accumulation for Enhanced Therapeutics

Agglomeration of therapeutic nanoparticles in response to tumor microenvironments is a promising approach to enhance drug accumulation and improve therapeutic efficacy.Cytosine-rich DNA sequences show potential as ideal cross-linkers to drive nanoparticle agglomeration because they can sensitively respond to weak acidity and form interchain folding.However,the in vivo application of DNA is generally limited by its poor biostability;as a consequence,modifications with unprotected DNA cross-linkers can enhance the accumulation of nanoparticles twofold at the tumor site.Facing this challenge,we have designed and developed a protection and tumor-environment activation strategy to enable the in vivo application of a DNA cross-linker.Specifically,reactive oxygen species(ROS)-responsive polyethylene glycol(PEG)was modified on the nanoparticle surface together with the DNA crosslinker,which protects DNA from degradation during the blood circulation;meanwhile,when arriving at the tumor site,the nanoparticles shed the PEG shell as a response to ROS to uncover and activate the DNA cross-linkers.Using this strategy,a sevenfold enhancement in tumor accumulation was achieved owing to both superior pH sensitivity and improved stability of DNA cross-linkers.Finally,significantly improved therapeutic efficacy in in vivo anticancer treatment was realized by using this agglomeration strategy driven by protected and stimuli-activated DNA cross-linkers.