Design Of A Core-Shell Tecto Dendrimer Nanoplatform And Its Ultrasound-Enhanced Theranostic Property To Tackle Triple Negative Breast Cancer

Triple-negative breast cancer（TNBC）lacking progesterone receptor,estrogen receptor and human epidermal growth factor 2 receptor has the characteristics of strong invasiveness,easy metastasis and high recurrence rate,resulting in poor therapeutic efficacy and prognosis after traditional treatment.Therefore,it is urgent to develop novel diagnosis and therapy strategies.With the development of nanotechnology,nanocarriers provide possibility for precise diagnosis and efficient treatment of tumor.Nanomaterials can be constructed and modified to efficiently load and deliver drugs to tumor sites with an enriched concentration.In addition,two or more contrast and/or therapeutic agents can be integrated in one nanoplatform simultaneously for multimodal diagnosis,combination therapy or theranostics.However,due to easy clearance by the reticuloendothelial system during blood circulation and resistance by the dense stroma at the tumor tissue site,the enrichment of nanodrugs at tumor sites is still not ideal,which makes it difficult to achieve the required concentration for efficient treatment.It has been reported that modification of amphoteric ions on the surface of nanocarriers can reduce the non-specific adsorption of various proteins,prolonging its blood circulation time and increasing the aggregation of nanodrugs in the tumor area.Moreover,the literature has also proved that ultrasound-targeted microbubble destruction（UTMD）is a new strategy for nanodrugs to break through tumor mesenchymal resistance and enhance their enrichment inside tumor tissues.Among various carriers,polyamide-amine（PAMAM）dendrimers have shown great potential in biomedical applications such as gene and drug delivery,molecular imaging and tumor treatment due to their unique physicochemical properties,such as controllable molecular size,internal cavity,and large number of peripheral amino groups for easy modification.In particular,the core-shell tecto dendrimers（CSTDs）based on PAMAM dendrimers not only inherit the advantages of modifiability and non-immunogenicity of single generation dendrimers,but also overcome the limitations of low generation dendrimers such as low drug loading capacity,limited gene delivery efficiency,enabling CSTDs to be used as an excellent nanocarrier.Based on these,we used the generation three PAMAM dendrimer（G3）modified with Gd chelators-tetraazacyclododecane tetraacetic acid（DOTA）and the amino-terminated adamantane（Ad）as the shell（Ad-G3-DOTA）,and the generation five PAMAM dendrimer（G5）conjugated with the amino-terminatedβ-cyclodextrin（β-CD）as the core（G5-CD）,to construct core-shell tecto dendrimers（G5-CD/Ad-G3-DOTA,CSTDs）through supramolecular self-assembly,followed by further modification of 1,3-propane sultone（1,3-PS）and chelation of gadolinium(Gd³⁺)on the surface.Then the formed nanocomplex PCSTD-Gd was utilized to physically encapsulate chemotherapeutic drug doxorubicin（DOX）and electrostatically adsorb gene drug miR21 inhibitor（miR 21i）to form multifunctional theranostic nanoplatform（PCSTD-Gd/DOX/miR 21i）for magnetic resonance（MR）imaging mediated combined chemo-gene therapy of TNBC.Companied with UTMD,the accuracy of imaging diagnosis and therapeutic efficacy of combined treatment were further improved.The characterization results showed that the prepared the nanocarriers of PCSTD-Gd has relatively homogeneous and spherical morphology,and monodispersity with a size of 309 nm and surface potential of 16 m V,as well as good anti-fouling properties;the Gd ions were efficiently chelated on the surface of dendrimers,leading to good T₁relaxation properties(6.72 m M^-1s^-1).PCSTD-Gd nanocarriers had a high drug loading efficiency of 84.04%and the loaded drug was able to efficiently release in the tumor microenvironment.In vitro,the PCSTD-Gd/DOX/miR 21i had a significant inhibition effect of tumor cell,which was 1.4 times compared with PCSTD-Gd/DOX,demonstrating a significant synergistic effect of gene and chemotherapy.The PCSTD-Gd/DOX/miR 21i blocked the cell cycle in G1 phase and induced apoptosis of 37.6%cells.The antitumor mechanism of PCSTD-Gd/DOX/miR 21i at the molecular level was that it regulated the expression of related genes and proteins to inhibit the growth of cancer cells.In vivo,combinated with UTMD,MR imaging ability of the PCSTD-Gd/DOX/miR 21i could be enhanced in form of an increased signal to noise by 41%at the tumor site,and the blood perfusion inside the tumor also was improved with an increased fluorescence signal intensity of 12%in tumor.The change of tumor volume in mice during treatment further verified the synergistic therapeutic effect of DOX and miR21i,which was then able to be further enhanced by using UTMD in combination.In a word,the formed PCSTD-Gd/DOX/miR 21i can be used for MR imaging-guided gene/chemotherapy combination therapy,and the utilization of UTMD in combination can further increase the diagnosis accuracy of MR imaging and therapeutic efficacy of tumors.Therefore,the findings of thesis provide a novel idea to develop integrated nanoplatforms for efficient theranotics of tumors,especially of TNBC which lacks some related receptors for target therapy.