Fig. 6.

Effects of honokiol on killing temozolomide (TMZ)-resistant human glioma cells. Human TMZ-tolerant U87-MG-R9 cells were prepared by selection from human U87-MG glioma cells as described in "Materials and Methods". Morphologies of human U87-MG and U87-MG-R9 cells were observed and photographed (a). Cytotoxicity of TMZ at 100 μM to U87-MG and U87-MG-R9 cells was assayed using a colorimetric assay (b). Human U87-MG-R9 cells were exposed to 1, 5, 10, 20, 40, 60, 80, and 100 μM of honokiol for 72 h. Effects of honokiol on the cell number and morphology were evaluated (c). Cell viability was assayed using a colorimetric method (d). The 50% lethal concentration (LC₅₀) was calculated. Human U87-MG-R9 cells were pretreated with 1 mM 3-methyladenine (3-MA), an inhibitor of cell autophagy, for 1 h and then exposed honokiol (40 μM) for 72 h. Cell apoptosis was quantified using flow cytometry (e). Each value represents the mean ± SEM for n = 6. *, the value significantly differs from the respective control, p < 0.05