Doxorubicin-Loaded Carbon Dots Lipid-Coated Calcium Phosphate Nanoparticles for Visual Targeted Delivery and Therapy of Tumor

Abstract

Background: Carbon dots (CDs) have attracted extensive attention in recent years because of their high biocompatibility and unique optical property. But they could not be well applied in the drug delivery system to enable distribution in tumor sites with their low pH sensitivity. They are barriers for drug delivery. CDs as an imaging proper were conjugated with doxorubicin (DOX) lipid-coated calcium phosphate (LCP) nanoparticle, for a pH-sensitive nanocarrier and delivery of the antitumor drugs.

Materials and methods: CDs were prepared by one-step hydrothermal treatment of citric acid and ethylenediamine. The nanoparticles were simply prepared by using microemulsion technology to form calcium phosphate (CaP) core and further coated with cationic lipids.

Results: The structure was characterized by FTIR, XRD and TEM. In vitro release study revealed that DOX-CDs@LCP was pH dependent. The cytotoxicity assay demonstrated that it exhibited enhanced efficiency compared to the control group (DOX-CDs), but weaker than free DOX. The cellular uptake revealed that these pH-sensitive nanoparticles could be taken up effectively and deliver DOX into the cytoplasm to reach antitumor effect. The fluorescence imaging indicated that DOX-CDs@LCP mostly distributed in the tumor region due to the enhanced permeability and retention effect (EPR) to reduce its systematical toxicity. Importantly, an antitumor activity study demonstrated that the DOX-CDs@LCP nanoparticles had higher antitumor activity than any other groups and lower toxicity. The results showed that LCP could significantly promote the release in tumor microenvironment due to pH-response. The DOX-CDs could enhance load capacity and reduce drug premature releasing; real-time tracking of efficacy as confocal imaging contrast agent. Thus, DOX-CDs@LCP had antitumor capacity and lower systematic toxicity in tumor therapy.

Conclusion: DOX-CDs@LCP were proven as a promising tumor pH-sensitive and imaging-guided drug delivery system for liver cancer chemotherapy.

Keywords: bioimaging; calcium phosphate photodynamic therapy; carbon dots; pH-sensitive; therapy; tumor targeting.

Scheme 1

The DOX-CDs@LCP accumulated at the tumor site by the EPR effect (B) and CDs-DOX released at the low pH sites (A).

Figure 1

TEM image of CDs and DOX-CDs@LCP (A), and the spectra (B) and X-ray diffractograms (C) of CDs, DOX, DOX-CDs@CaP and DOX-CDs@LCP.

Figure 2

(A) In vitro release profile of DOX from DOX-CDs@LCP nanoparticles at pH 7.4 and 5.5, n=3, respectively. (B) In vitro release profile of DOX from DOX-CDs@LCP nanoparticles and DOX@LCP nanoparticles at pH 7.4, respectively, n=3.

Figure 3

Cell viability of free DOX, DOX-CDs and CDs@LCP nanoparticles against HepG2 cells at different concentrations for 48 hrs.

Figure 4

FCM results of cellular uptake in HepG2 cells after incubation with free DOX, DOX-CDs@LCP nanoparticles incubated for 2 and 4 hrs.

Figure 5

Confocal microscope images of HepG2 cells incubated with DOX, DOX-CDs, DOX-CDs@LCP for 4 hrs. Cell nuclei were stained with DAPI and the co-localization was confirmed by the intensity of cells by overlaying the fluorescent signals. Scale bar: 20 μm.

Figure 6

Real-time fluorescence imaging of tumor-bearing mice (H22) after injection of DOX, DOX-CDs and DOX-CDs@LCP by tail vein.

Figure 7

The mean tumor volume (A), body weight (B) and tumor weight (C) of Kunming mice bearing H22 cells, on intravenous administration of the different formulation (n=10). **P<0.01, and ***P<0.001.