Doxorubicin-loaded Carbon Dots As A Novel Drug Delivery System For Nucleus Targeted Cancer Therapy

Chemotherapy is widely applied against various kind of carcinoma.Unfortunately,chemotherapeutics are indiscriminate and also kill normal healthy cells,resulting in serious side effects.This non-productive and destructive distribution of chemotherapeutics is regarded as one of the largest problems associated with chemotherapy.Recently,the application of carbon dots in cancer therapy has attracted considerable attention due to their attractive properties such ass biocompatibility and low toxicity.At present,although the study of drug-loaded carbon dots as a biomedicine delivery system for medical therapy is more thorough,their applications in oral tumor disease have rarely been reported,while oral tumor disease is insensitive to chemotherapeutics.Objective:To synthesize CDs and a novel drug delivery system combining CDs and DOX.Their characterizations are also discussed here.To compare the therapeutic efficiency between CD-DOX system and free DOX,and explore the mechanism of this drug delivery system.Methods:Section 1 Preparation and characterization of CDs and CD-DOX complexesThe CDs were fabricated through the thermolysis of milk.For complex formation,CD solution and DOX solution were mixed and allowed to react for 24h on an incubator shaker in the dark.Fluorescence spectroscopy,UV-vis spectroscopy,Contact angle,Zeta potential,TEM,SEM,AFM,FT-IR spectrum,XPS,and XRD were used to show the morphology and characteristics of fabricated CDs and CD-DOX complexes.Section 2 Antitumor efficacy of CD-DOX complexes in vitro DOX loading efficiency was assessed by a fluorescence spectrophotometer and calculated according to a calibration curve.The drug release experiment of CD-DOX solution was performed across a range of different pH values(pH 7.4,6.8,5.0)and the released DOX was measured by fluorescence spectrophotometer,drawing the release curve.L929 cells and ACC-2 cells were used in our study.The cytotoxicity of CDs,free DOX and CDs-DOX complexes in vitro was measured by CCK-8 assay.The particles'localization and intracellular uptake in ACC-2cells were examined by confocal microscopy.Cell cycle and apoptosis analysis were observed by flow cytometry.Data were analyzed via the Student's t-test using GraphPad Prism 6.0.Results:Section 1 Preparation and characterization of CDs and CD-DOX complexesThe fabricated CDs in our study exhibited a spherical morphology.The contact angle of the CDs was 10.4°,demonstrating that the fabricated CDs were highly hydrophilic.The CDs exhibited a zeta potential value of-7.38 mV.The morphology and characteristics of CDs were consistent with results reported previously,which gave the evidence of successful fabrication.CD-DOX complexes displayed a blue shift when excited at 360 nm.In the UV-vis absorption spectra,CD-DOX complexes also had a blue shift.The extra absorption peaks at 1200 cm-1 assigned to C-N stretching was observed for CD-DOX in FT-IR spectrum.In the XPS spectra,the new band of C-N was also observed.All of these results confirmed the complex conjugation of CDs and DOX.Section 2 Antitumor efficacy of CD-DOX complexes in vitroThe loading efficiency of DOX was about 87%.At pH 5.0,the quantity of release DOX was highest.And the release of DOX continued slowly for up to 72 h.The results of CCK-8 showed that CDs were low-cytotoxicity to L929 cells and nearly non-cytotoxic in concentrations considered to be reasonable for practical application.Meanwhile,CD-DOX complexes displayed a higher cytotoxicity to ACC-2 cells than free DOX but a lower cytotoxicity for DOX-insensitive L929 cells than free DOX.CD-DOX complexes showed distinct nuclear localization according to the images of confocal laser scanning microscopy.Flow cytometry indicated that for the cancer cells,incubation with the CD-DOX complexes resulted in a higher degree of apoptosis,in comparison to free DOX.Conclusion:1.CDs exhibit the favorable properties of intense photoluminescence,low toxicity and good biocompatibility.The synthetic method of CDs is more environmentally friendly than traditional approaches.2.The differences between the CDs and CD-DOX complexes confirm the successful preparation of the CD-DOX complexes.The complexes exhibit pH-dependent behavior.3.The CD-DOX complexes enhance antitumor behavior toward ACC-2 cells and reduce cytotoxicity to DOX-insensitive L929 cells.4.The CD-DOX complexes increase the antitumor efficacy of DOX by nuclear localization and the apoptotic pathway.