Study Of Dendrimer-based Nanomedicines For The Delivery Of Toll-like Receptor Agonist

In recent years,the strategies of cancer treatment have become more diversified,and novel immunotherapy has become a new option.Resiquimod(R848),a Toll-like receptor 7/8 agonist,can be used as adjuvant to activate antigen-presenting cells and enhance immunotherapy by improving the tumor immune microenvironment.However,R848 is a water-insoluble small molecule with low bioavailability and serious systemic toxicity.The development of appropriate drug carriers is an important means to improve efficacy and reduce toxicity.Dendrimer has precise molecular structure,abundant surface functional groups and hydrophobic cavities,which has been widely used as drug delivery systems.Herein,this thesis adopted dendritic macromolecules as delivery carriers of R848 through physical encapsulation and chemical conjugation,respectively.After the study of drug loading behavior,the nanomeidicines were further investigated for cancer immunotherapy.Specific contents were as followings:(1)Based on the structural characteristics of the fourth generation of PAMAM(G4PAMAM),we modified the surface of G4-PAMAM with different tertiary amines,and discussed the physical encapsulation behavior of the modified materials on R848.The results showed that both G4-DEEA and G4-C7A could efficiently encapsulate R848 with the drug loading capacity higher than 35wt%,and the drug loading content of G4-C7A was slightly higher than that of G4-DEEA.We also found that with the increase of hydrophobicity of the surface modified molecules,the interactions(such as hydrophobicity,hydrogen bonding,etc.)between the carrier and the drug were enhanced.1H NMR technique implied that these interactions mainly occurred within the periphery of the PAMAM derivatives.Finally,burst drug release of R848 was observed in these systems,which indirectly confirmed that the physical interactions between carrers and drugs were not strong encough.(2)A series of R848 derivatives were prepared by an innovative and more general synthetic strategy for.These derivatives maintained the the biological functions of R848 as confirmed in various in vitro studies.Subsequently,we synthesized a linear-dendritic polyethylene glycolpolylysine polymer(PL)and conjugated it with one of the R848 derivatives(R848-HSEA)to prepare a glutathione(GSH)-responsive polymer prodrug(PLRS).PLRS could self-assemble into nanoparticles with the size around 35 nm.Reductive environment induced R848 release was observed.In vivo experiments have shown that PLRS could effectively inhibit the growth of 4T1 tumors.The mechanism studies indicated that PLRS could significantly enhance the T cell response,and improve the therapeutic effect of immune checkpoint inhibitor aPD-1.