Daunorubicin-TiO2 nanocomposites as a "smart" pH-responsive drug delivery system

Abstract

Daunorubicin (DNR) has a broad spectrum of anticancer activity, but is limited in clinical application due to its serious side effects. The aim of this study was to explore a novel "smart" pH-responsive drug delivery system (DDS) based on titanium dioxide (TiO(2)) nanoparticles for its potential in enabling more intelligent controlled release and enhancing chemotherapeutic efficiency of DNR. DNR was loaded onto TiO(2) nanoparticles by forming complexes with transition metal titanium to construct DNR-TiO(2) nanocomposites as a DDS. DNR was released from the DDS much more rapidly at pH 5.0 and 6.0 than at pH 7.4, which is a desirable characteristic for tumor-targeted drug delivery. DNR-TiO(2) nanocomposites induced remarkable improvement in anticancer activity, as demonstrated by flow cytometry, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and nuclear 4',6-diamidino- 2-phenylindole staining. Furthermore, the possible signaling pathway was explored by western blot. For instance, in human leukemia K562 cells, it was demonstrated that DNR-TiO(2) nanocomposites increase intracellular concentration of DNR and enhance its anticancer efficiency by inducing apoptosis in a caspase-dependent manner, indicating that DNR-TiO(2) nanocomposites could act as an efficient DDS importing DNR into target cancer cells. These findings suggest that "smart" DNR delivery strategy is a promising approach to cancer therapy.

Keywords: TiO2 nanoparticles; apoptosis; cancer; daunorubicin; drug delivery system; pH-responsive.

Figure 1

Transmission electron microscopic image (A), electron diffraction patterns (B), and high-resolution transmission electron microscopic image (C) of titanium dioxide nanoparticles.

Figure 2

Schematic representation and photographic image (inset) of daunorubicin loading onto titanium dioxide nanoparticles through the formation of daunorubicintitanium dioxide nanocomposites. Abbreviations: DNR, daunorubicin; Nps, nanoparticles; TiO₂, titanium dioxide.

Figure 3

In vitro daunorubicin release behavior at pH 7.4, 6.0, and 5.0. Abbreviations: DNR, daunorubicin; DNR-TiO₂, daunorubicin-titanium dioxide nanocomposites; TiO₂, titanium dioxide.

Figure 4

Fluorescent microscopic images of K562 cells (A) treated with free daunorubicin (left panel) and titanium dioxide nanoparticles loading daunorubicin as a drug delivery system (right panel). Comparison of the respective average intracellular fluorescence intensity is also shown (B). Concentrations of daunorubicin and titanium dioxide nanoparticles are 0.5 μg/mL and 10 μg/mL, respectively. Note: Data expressed as mean ± standard deviation (n = 3). Abbreviations: DNR, daunorubicin; Nps, nanoparticles; TiO₂, titanium dioxide.

Figure 5

Cytotoxic effect of daunorubicin or daunorubicin-titanium dioxide nanocomposites on K562 leukemia cells. Microscopic images of K562 cells after different treatments for 48 hours are shown inset: (A) untreated cells as control, (B) titanium dioxide nanoparticles, (C) daunorubicin alone, and (D) daunorubicintitanium dioxide nanocomposites. Concentrations of daunorubicin and titanium dioxide nanoparticles are 1 μmol/L and 10 μg/mL, respectively. Note: Data expressed as mean ± standard deviation (n = 3). Abbreviations: DNR, daunorubicin; DNR-TiO₂, daunorubicin-titanium dioxide nanocomposites; Nps, nanoparticles; TiO₂, titanium dioxide.

Figure 6

Nuclear morphologic changes of K562 leukemia cells after different treatments for 48 hours: (A) untreated cells as control, (B) titanium dioxide nanoparticles, (C) daunorubicin alone, and (D) daunorubicin-titanium dioxide nanocomposites. Concentrations of daunorubicin and titanium dioxide nanoparticles are 0.5 μg/mL and 10 μg/mL, respectively. Notes: Magnification: ×400. Arrows indicate cells with apoptotic nuclear condensation and fragmentation.

Figure 7

Expression of caspase 3 in K562 cells by western blotting analysis. After normalization by corresponding β-actin expression, protein expression levels of caspase 3 were determined by densitometry scans to obtain quantitative data. Note: Data expressed as mean ± standard deviation (n = 3). Abbreviations: DNR, daunorubicin; DNR-TiO₂, daunorubicin-titanium dioxide nanocomposites; Nps, nanoparticles; TiO₂, titanium dioxide.

Figure 8

Schematic illustration of the possible process of distinct improvement in anticancer activity by the novel pH-responsive drug delivery system based on titanium dioxide nanoparticles for daunorubicin. Abbreviations: DNR, daunorubicin; Nps, nanoparticles; DNR-TiO₂, daunorubicin-titanium dioxide nanocomposites; TiO₂, titanium dioxide.