A, the effect of let-7b mimic, paclitaxel or gemcitabine on TUBB3 protein in A549, NIH-H1975, Panc-1 and BxPC-3 cells was analyzed by Western blotting. B, the effect of let-7b mimic, paclitaxel or gemcitabine on TUBB3 mRNA in A549, NIH-H1975, Panc-1 and BxPC-3 cells was analyzed by qRT-PCR. C, the effect of let-7b mimic, paclitaxel or gemcitabine on RRM2 protein in A549, NIH-H1975, Panc-1 and BxPC-3 cells was analyzed by Western blotting. D, the effect of let-7b mimic, paclitaxel and gemcitabine on RRM2 mRNA in A549, NIH-H1975, Panc-1 and BxPC-3 cells was analyzed by qRT-PCR. Each experiment was carried out at least 3 times. Data represent the mean ± SEM. *, p < 0.05; **, p < 0.01.