DNAzyme Based Multifunctional Nanocarriers For Targeted Gene Therapy In Breast Cancer

Breast cancer is a major malignant tumor that harms women's health.The occurrence and progress of breast cancer involves the changes of multiple genes.With the rapid development of molecular biology techniques,more and more breast cancer related genes were identified.Gene therapy has been recognized as a new way for breast cancer therapy and shows great clinical application prospect.Among numerous gene therapy strategies,DNAzymes,which can be engineered to bind to complementary sequences in a target mRNA and cleave it at predetermined phosphodiester linkages,are particularly attractive due to their easy,low-cost synthesis and modification,lower toxicity,high selectivity and stability,and significant catalytic efficiency.With the aid of DNAzyme,we can silence target genes,which induce the deterioration of cancer,to specially inhibit tumor growth,for individualized treatment.Although the DNAzymes showed some promise,safe and effective delivery of DNAzyme in vivo and high efficiency targeted gene silencing remain the critical hurdles for their practical applications.Here we developed two multifunctional nanosystems,biodegradable DNAzyme nanoflowers(DNFs)and a DNAzyme-nanosponge therapeutic platform,for breast cancer gene therapy.1.The intrinsic degradability and biocompatibility of former gene therapy systems together with their low therapeutic effect limited their clinical applications.To overcome these limitations,we present biodegradable,multifunctional DNAzyme nanoflowers for enhanced cancer therapy.The DNFs were easily constructed by introducing aptamer,EGR-1 DNAzyme and survivin DNAzyme sequences into an RCA template,which together provide cell targeting and dual gene-silencing capability.Moreover,the DNFs also can be used as drug carrier for targeted drug delivery.In vitro and in vivo studies have shown that the DNFs have high silencing efficiency at the mRNA and protein expression levels,as well as pro-apoptotic effects and enhanced antitumor activity.2.The thermoresistance,is accompanied by a heat shock response in PTT,which decreases the photothermal therapeutic efficacy.To overcome thermoresistance,we have developed a novel nanosponge-ICG therapeutic platform for highly efficient PTT using DNAzymes.The nanosponge was constructed by simply assembling a cationic polymer and a long single strand of DNA,which can be customized with multivalent DNAzyme sequences using the RCA method.The multivalent DNAzyme can efficiently silence the HSP70 gene to increase the sensitivity of tumor cells to heat,enhancing photothermal effect.In vitro studies demonstrated the capability of this therapeutic platform to sensitize MCF-7 cells to heat by inhibiting the overexpression of HSP70.Moreover,the nanoplatform can act as an efficient multimode imaging agent to trace its accumulation in tumour tissue.In vivo studies show that the nanosponge-ICG can efficiently inhibit tumor growth,and have no obvious toxicity on organs and blood.Considering its enhanced therapeutic effect and biocompatibility,this therapeutic platform is expected to be used in a combination of photothermal and gene therapy for breast cancer.In summary,aiming at overcoming the physical barriers of gene drug delivery,and ensuring the safety and efficiency of the gene drug in vivo,we use DNAzyme as gene silencing agent to fabricate two nano-carriers for gene therapy toward breasr cancer,both of which showed highly effective antitumor activity in vitro and in vivo.Therefore,the results of this thesis provided basic research data for the clinical application of DNAzyme as gene drugs in the future.Undoubtedly,it will produce important significance.