Among the different morphological nanostructures, the hierarchical particles from nanometer to micrometer dimensions reveal the great desirable properties. They have been attracting considerable attention, owing to their widespread applications in catalysis, chemical reactors, drug delivery, controlled release of various substances, protection of environmentally sensitive biological molecules, and lightweight filler materials MI-503 [19, 32–37]. Highly orderly hierarchical and pH value-sensitive calcium carbonate can stably preserve drug under physiological conditions and selectively release in the intracellular acid environment . Han et al. reported the mesoporous hollow CaCO3 spheres prepared in guanidinium ionic
liquid, but the surface area of those products is very low, even only 17 m2/g . It is still attractive to prepare mesoporous selleckchem high-surface area carbonates with unique morphology and structure. Herein, a crystallization of mesoporous calcium carbonate nanospheres (CCNSs) with hierarchical structure was prepared by a new facile binary solvent method which is involved in the multistage self-assembly of calcium carbonate crystallites into hierarchical spheres under the templating effect of CO2 (as shown in Figure 1). These prepared CCNSs have high surface areas,
even up to 82.14 m2/g, and show the typical mesoporous properties. The method is mild, easily performed, Cediranib (AZD2171) and environment-friendly, which is based on a biomimetic system supported liquid membrane used by Sun  and mixed-solvent method used by Qian . Etoposide-loaded strontium carbonate nanoparticles have been studied by our group . However, there could be an existing problem about the Ralimetinib supplier enrichment of strontium toxicity after strontium carbonate degradation in vivo. Therefore, CCNSs were used as the carrier for etoposide in this study; the drug loading efficiency and the drug release behaviors were also evaluated. Moreover, in vitro cellular experiments with MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl
tetrazolium bromide) assay and fluorescence-activated cell sorter (FACS) analysis were carried out to evaluate the anticancer effect of etoposide-loaded CCNSs. Meanwhile, confocal laser scanning microscopy (CLSM) image was utilized to investigate the uptake of CCNSs by cancer cells. The possible mechanism of the targeted delivery of the ECCNSs was also discussed based on the obtained results and related references. Figure 1 Schematic illustration for the synthesis of CCNSs. Methods Materials Etoposide (≥98%) was a kind gift from the University of Science and Technology of China. Dimethyl sulfoxide (DMSO) and MTT formazan were purchased from Sigma Chemical Co. (St Louis, MO, USA). CaCl2 (analytical reagent (AR)), Na2CO3 (AR), citric acid (AR), HCl (36%–38%), and ethanol (AR) were purchased from Sinopharm Chemical Regent Co., Ltd. (Shanghai, China) and were used without further purification.