Dexamethasone Enhances FRα-mediated Targeted Delivery Of Environmentally Sensitive Nanoparticles And Antitumor Efficacy Evaluation

Folate receptor(FR)is highly expressed on the surface of various tumor cells and can be used as a target molecule for active targeting.In recent years,folic acid(FA)-modified nano-delivery system(NDS)has been widely used for delivery of drug or gene.However,excessive modification of NDS by FA can lead to poor water solubility and large steric hindrance which reduces cellular uptake.The efficacy of tumor targeted therapy for FAfunctionalized NDS depends largely on the abundance of FR on the surface of cancer cells.However,natural immunoglobulin M(IgM)weakens the ability of FA-functionalized NDS to recognize FR,reducing the effective delivery of FA-functionalized NDS to tumor tissue.It was reported that dexamethasone(Dex)can induce the amplification of FRα,and its immunosuppressive effect can attenuate the effect of serum immunoglobulin M(IgM)on FA-modified NDS.To deal with the insufficient targeting efficiency of FA-functionalized vectors,we propose a sequential therapy of dexamethasone combined with FAfunctionalized microenvironment-sensitive NDS to enhance targeting effect of the NDS by FRa amplification and NDS clearance reduction in circulation,which was proven to significantly enhance the anti-tumor effect of drugs or genes.Chapter 1:A brief overview of current situation and therapeutic research progress of different tumors.Applications of tumor microenvironment-sensitive drug delivery system in targeted therapy were also summarized in this chapter.Particularly,the research status of FR-based nano-delivery system and the role of METTL3 in tumor occurrence,development and treatment were introduced.Chapter 2:A pH/reduction-responsive FA-functionalized micelle was prepared by grafting folic acid(FA),reduced sensitive cholesterol(CET)and pH-sensitive 2’3dimethylmaleic anhydride(DMMA)onto chitosan oligosaccharide(CSO)to obtain FAmodified CET-CSO-DMMA(FCSD).The pH/reduction-responsive FA-functionalized doxorubicin(DOX)micelles(FCSD/DOX)were prepared by ultrasonic method loading DOX to FCSD.In this study,a sequential therapy of Dex-induced FRα amplification and immunosuppression combined with FA-functionalized DOX micelles to increase tumor killing has been proposed.Dex selectively increases the expression of FRa on the surface of M109 cells,reduces the content of serum immunoglobulin,and weakens the effect of natural IgM on the tumor targeting of FCSD/DOX.Additionally,the negative surface charge of FCSD/DOX was reversed under extracellular pH(pHe)conditions,which promotes the uptake of FA-functionalized DOX micelles.After internalization,disulfide bonds in the micelle were broken with the stimulation of intracellular GSH,leading to the disintegration of micelles and the rapid release of DOX.The results showed that the tumor inhibition rate of sequential therapy was 81.01%which was significantly enhanced compared with FCSD/DOX alone treatment.Therefore,we should re-recognize the sequential therapy of dexamethasone combined with FA-functionalized NDS for FR-positive lung cancer patients.Chapter 3:Multi-drug resistance(MDR)of breast cancer is characterized by crossresistance to multiple chemotherapeutic drugs,which limits the choice of treatment.The expression level of m6A methylase METTL3 is positively correlated with chemotherapy resistance of cancer cells,and down-regulation of METTL3 may increase the sensitivity of different chemotherapy drugs.To further weaken the effect of serum IgM on FAfunctionalized carriers,a FA-functionalized cationic liposome(FLip)was coated with environmentally sensitive PEG shell material(sPEG)for delivery of Dex or METTL3 siRNA(siMETTL3)and DOX.Stimulated by pHe,the sPEG layer peeled off the surface of Dex-FLip or siMETTL3/DOX-FLip,exposing positive charge and active targeting ligand FA.Due to the up-regulation of FRα on doxorubicin-resistant breast cancer cells(MCF7/ADR)by sPEG-Dex-FLip,the cellular uptake and lysosomal escape of siMETTL3/DOXFLip mediated by FR were promoted.And the down-regulation of intracellular METTL3 protein resulted in decreased expression levels of MDR1,BCRP and Bcl-2 proteins,and increased the expression of Bax protein,thus reversing drug resistance and improving the sensitivity of MCF-7/ADR cells to DOX.Simultaneously,DOX gradually diffused to the nuclei and promoted the apoptosis of tumor cells.In vivo,sPEG-FLip exhibited excellent tumor-target effect with the up-regulation of FRa by Dex,and both siMETTL3 and DOX could be effectively delivered to tumor tissues.Pharmacodynamic evaluation demonstrated that sPEG-siMETTL3/DOX-FLip could reverse the drug resistance of mice and make DOX exert the maximum tumor killing effect.Most importantly,the sequential treatment showed higher anti-tumor efficacy compared with sPEG-siMETTL3/DOX-FLip treatment alone.In a word,the sequential therapy combining FRα amplification effect with siMETTL3/DOX administration is a more scientific therapeutic strategy to treat drug-resistant breast cancer in vivo.