Design, Synthesis And Application Of Nanoprodrug System Based On Bond-cleavage Reactions

Three nanoprodrugs based on bond-cleavage reactions were designed and synthesized.The results indicate that both the internal stimuli such as overexpressed glutathione(GSH)in cancer cells or external stimuli such as bioorthogonal catalyst could trigger the bond-cleavage reactions and thereby release parent drugs for therapy and restore fluorescent emission for imaging.The main results of this reseach are given below:1)Comprehensive understanding of signaling pathways regulating cancer progression has led to tremendous advances of molecularly targeted therapies.The epidermal growth factor receptor(EGFR)pathway is an attractive target for cancer therapy,and targeting multiple key elements in the pathway may further facilitate therapeutic efficacy.Herein we demonstrate an EGFR-targeted nanoprodrug for in vivo imaging and tumor inhibition,which is assembled by a disulfide-bridged quercetin(QSSQ)and an EGFR inhibitor erlotinib.QSSQ is synthesized via chemical manipulation of multiple phenolic hydroxyl groups on quercetin;and the nanoprodrug is then fabricated through the disulfide-facilitated assembly of QSSQ and erlotinib.The nanoprodrug is stable in physiological environment,whereas overexpressed glutathione(GSH)in tumor tissue breaks the disulfide bridge,thereby disrupting the nanostructure and releasing active drugs quercetin and erlotinib.Upon release,erlotinib serves as an active drug blocking the EGFR tyrosine kinase,and quercetin generates strong aggregation-induced emission(AIE)of fluorescence for imaging drug release and acts as another drug inhibiting the downstream EFGR signaling,as evidenced by Western blotting analyses.The combined action thereof results in remarkable antitumor efficacy towards xenograft tumor-bearing mice.2)Bioorthogonal bond-cleavage reactions have emerged as promising tools for manipulating biological processes,while the therapeutic effect of these reactions in vivo needs to be explored.Herein a bioorthogonal-activated prodrug was developed for bioimaging and therapy,which is composed of a Pd-mediated cleavable propargyl,a coumarin fluorophore and a potent anticancer drug.In vitro investigations show that,the presence of a Pd-complex induces the cleavage linker and trigger the cascade of reactions,therebyactivating the coumarin fluorophore for imaging and releasing the anticancer drug for therapy.Both the prodrug and Pd complex were then separately encapsulated into phospholipid liposomes to form a two-component bioorthogonal nanosystem.The lyposomal nanosystem can be readily internalized by HeLa cells and displays strong intracellular fluorescence under one-or two-photon excitation,indicating the release of the active drug in cells as a result of the Pd-mediated bioorthogonal bond-cleavage reaction.More importantly,the nanosystem shows considerable high activity and exerts efficient inhibition towards tumor growth in a mouse model.This work demonstrates that,if properly formulated,a bioorthogonal system can perform well in vivo.This strategy may offer a new approach for designing bioorthogonal prodrugs with imaging and therapeutic capability.3)Another bioorthogonal nanoprodrug system was designed based on the tetrazine(TZ)catalyzed bond-cleavage reaction.The prodrug was constructed by incorporating a vinyl group,an anticancer drug camptothecin,a self-immolative linker and a near infrared fluorescent dye Nile blue derivative into a single molecule.The presence of TZ catalyst leads to the release of CPT and restores the fluorescent emission of the dye,thereby realizing the therapy and fluorescence monitoring of drug release.To enhance the biocompatibility of the prodrug and prevent the premature bioorthogonal reactions before cellular internalization during drug delivery by intravenous administration,we respectively loaded the prodrug and the catalyst into different phospholipid vesicles,forming a two-component bioorthogonal nanosystem.The liposomal prodrug shows highly controllable cytotoxicity toward different cancer cells and remarkable antitumor efficacy towards xenograft tumor-bearing mice.In summary,these bond-cleavage nanoprodrugs can not only realize real-time monitoring drug of drug,but also show enhanced cytotoxicity and tumor inhibition effect in vivo.We suppose these strategies may offer new theranostic approachs for design and application of anticancer prodrug system.