Mechanism of apoptotic induction on T24 cells by honokiol and its synergistic anticancer effect in combination with hydroxycamptothecin.

OBJECTIVE: To investigate the mechanism of honokiol (HNK) on bladder cancer cells and its synergistic anticancer effect with hydroxycamptothecin (HCPT). METHODS: Control, HNK, HCPT, and HNK plus HCPT groups were established. The morphological characteristics of T24 cells were examined microscopically. The maximal experimental concentration of HNK and HCPT were determined according to IC10 detected by MTT. T24 cell viability and the percentage of apoptotic cells were assessed on the basis of MTT and flow cytometric analysis. The expression of caspase-3, caspase-9, phosphorylated nuclear factor-kappa B (NF-κB)-p65, Akt, and extracellular signal-regulated kinase (ERK) proteins were analyzed by Western blot. RESULTS: Apoptosis in T24 cells was observed microscopically in both the HNK and HCPT groups and even more obvious in the HNK plus HCPT groups. The percentage of T24 cell viability decreased down to 19.41% , and the percentage of apoptotic cells rose to 54.08% when treated with HNK plus HCPT in an HNK dose-dependent manner. The induction of caspase-3 and caspase-9 proteins and the inhibition of phosphorylation of NF-κB-p65, Akt, and ERK proteins in T24 cells were demonstrated in the HNK groups, and more significantly in the HNK plus HCPT groups, but not in the HCPT group. CONCLUSION: The anticancer effect of HNK may be due to the activation of the caspase pathway and inhibition of phosphorylation of NF-κB, Akt, and ERK. HNK in combination with HCPT produces a synergistic cell-killing effect on bladder cancer cells.