Figure 6 The release curves of DOX-loaded beta-CD nanocage in acidic environment (pH 4.5 PBS) (a), reduction environment (5 mM GSH) (b) and normal physiological environment (pH 7.4 PBS) (c).
3.3 The cytocompatibility of drug-free beta-CD nanocage and cell-killing effect of DOX-loaded beta-CD nanocage
After confirming the structure, characterizing the size, and testing the drug release performance, the cytocompatibility of drug-free beta-CD nanocage and the cell-killing effect of DOX-loaded beta-CD nanocage were further evaluated in vitro using a CCK-8 method. As shown in Figure 7, drug-free samples demonstrated good biocompatibility with over 80% cell viability at a concentration of 800 ng/ml. This result suggests that the composition of the beta-CD nanocage is almost non-toxic. Efficient delivery of DOX to tumor cells and killing tumor cells are crucial for using this proposed beta-CD nanocage. Therefore, SKOV 3 cells were incubated in acidic, GSH, and normal environments to verify the cell-killing effect of DOX-loaded beta-CD nanocage. In the acidic culture environment, DOX-loaded beta-CD nanocage exhibited an outstanding cell-killing effect with an IC50 of 600 ng/ml DOX-loaded beta-CD nanocage, equivalent to a DOX concentration of 225 ng/mL. In the GSH culture environment, DOX-loaded beta-CD nanocage also showed a superior cell-killing effect (IC50 of 700 ng/ml DOX-loaded beta-CD nanocage) but lower than in the acidic culture environment. In the normal culture environment, DOX-loaded beta-CD nanocage demonstrated a lower cell-killing effect. The proposed beta-CD nanocage with acid/reduction-responsive properties stands out from the normal physiological environment. When free DOX was directly treated with Skov 3 cells, the cell-killing rate was the highest, as shown in Figure 7(f), with the tumor cells exhibiting the lowest cell viability. These cell killing tests suggest that the beta-CD nanocage can self-regulate drug release, especially in the tumor microenvironment, effectively avoiding nonspecific release. Additionally, the beta-CD nanocage improved the drug release behavior in the tumor microenvironment to minimize toxicity to normal cells and maximize the anti-tumor effect.