Abstract: BACKGROUND: The low catalytic activity and lack of targeting of commonly used metal ions have severely limited the clinical application of chemodynamic therapy in tumor treatment. On the other hand, although the composite nanoplatforms are endowed with tumor-targeting functions by surface functionalization, the lack of tumor microenvironment acidity also severely weakens the efficacy of chemodynamic therapy.
OBJECTIVE: To prepare novel composite nanoplatforms and assess their feasibility to enhance the effects of chemodynamic therapy at the cellular level.
METHODS: SLC-0111-loaded zeolite imidazole framework-8 doped with divalent iron ions (Fe2+) and divalent cobalt ions (Co2+) (Fe-Co/ZIF-8@SLC-0111) was synthesized by ion-exchange reaction and self-assembly, and loaded with hyaluronic acid (HA) by electrostatic adsorption, followed by obtaining the target nanoparticles Fe-Co/ZIF-8@SLC-0111-HA (abbreviated as FC-S). Meanwhile, nanoparticles Fe-Co/ZIF-8-HA (abbreviated as FC) without SLC-0111 were synthesized by the same method. The nanocomposite platform was tested for particle size, zeta potential, surface morphology, in vitro reactive oxygen species generation, and ability to consume glutathione. Human osteosarcoma cell MG-63 and mouse fibroblast cell L929 were used as experimental subjects. The cytotoxicity of FC-S was detected by CCK-8 assay. Human osteosarcoma cell MG-63 was used as the experimental object to detect the cell internalization of FC-S. In addition to H2O2, the effects of FC-S and FC on intracellular pH, carbonic anhydrase 9 protein expression, cell viability and apoptosis, intracellular reactive oxygen species and glutathione content, and mitochondrial membrane potential were investigated.
RESULTS AND CONCLUSION: (1) The FC-S composite nanoplatform was successfully prepared with a well-defined rhombic dodecahedral structure, uniform size and good dispersion. Its particle size was about 323 nm; zeta potential was about -11.1 mV, and the nanoplatform had a certain reactive oxygen species generation capacity in vitro. (2) FC-S nanoplatforms accumulated intracellularly in a time-dependent manner and could successfully escape from lysosomes. When the mass concentration of FC-S was ≤ 20 µg/mL, there was no obvious cytotoxicity to MG-63 cells and L929 cells, and 20 µg/mL FC-S was selected to act on MG-63 cells in subsequent experiments. (3) Compared with FC group, the protein expression of carbonic anhydrase 9 in MG-63 cells in FC-S group was decreased (P < 0.01); the intracellular acidic environment was enhanced; the content of reactive oxygen species was increased (P < 0.001); the mitochondrial damage was aggravated; the number of dead cells was increased, and the apoptosis rate was increased (P < 0.001). (4) The results indicate that FC-S, as a novel composite nanoplatform, can effectively improve the weakly acidic microenvironment in tumor cells and enhance the level of intracellular reactive oxygen species production, thus enhancing the efficacy of chemodynamic therapy.

Key words: nanoplatform, chemodynamic therapy, carbonic anhydrase 9, carbonic anhydrase 9 inhibitor, reactive oxygen species, apoptosis