Aim: To investigate the cytotoxic effects of piperonal ciprofloxacin hydrazone (QNT4), a novel antibacterial fluoroquinolone derivative, against human hepatocarcinoma SMMC-7721 cells.
Methods: Human hepatocarcinoma cells (SMMC-7721), human breast adenocarcinoma cells (MCF-7) and human colon adenocarcinoma cells (HCT-8) were tested. The effects of QNT4 on cell proliferation were examined using MTT assay. Cell apoptosis was determined using Hoechst 33258 fluorescence staining, TUNEL assay and agarose gel electrophoresis. The topoisomerase II activity was measured using agarose gel electrophoresis with the DNA plasmid pBR322 as the substrate. Mitochondrial membrane potential (Δψm) was measured using a high content screening imaging system. Protein expression of caspase-9, caspase-8, caspase-3, p53, Bcl-2, Bax, and cytochrome c was detected with Western blot analysis.
Results: Treatment with QNT4 (0.625-10 μmol/L) potently inhibited the proliferation of the cancer cells in time- and dose-dependent manners (the IC(50) value at 24 h in SMMC-7721 cells, MCF-7 cells and HCT-8 cells was 2.956±0.024, 3.710±0.027, and 3.694±0.030 μmol/L, respectively). Treatment of SMMC-7721 cells with QNT4 (0.2146, 2.964, and 4.600 μmol/L) for 24 h dose-dependently increased the percentage of apoptotic cells, elicited characteristic DNA "ladder" bands, and decreased the mitochondrial membrane potential. QNT4 dose-dependently increased topoisomerase II-mediated DNA breaks while inhibiting DNA relegation, thus keeping the DNA in fragments. Treatment of SMMC-7721 cells with QNT4 significantly increased cytochrome c in the cytosol, and decreased cytochrome c in the mitochondrial compartment. QNT4 (3-7.39 μmol/L) significantly increased the protein expression of p53, Bax, caspase-9, caspase-3, and the cleaved activated forms of caspase-9 and caspase-3 in SMMC-7721 cells. In contrast, the expression of Bcl-2 was decreased, while caspase-8 had no significant change.
Conclusion: QNT4 induced the apoptosis of SMMC-7721 cells via inhibiting topoisomerase II activity and modulating mitochondrial-dependent pathways.