The development of novel targeted
therapies has become an important research focus for
lung cancer treatment. Our previous study has shown
leptomycin B (LMB) significantly inhibited proliferation of
lung cancer cells; however, p53 wild type
lung cancer cells were resistant to LMB. Therefore, the objective of this study was to develop and evaluate a novel therapeutic strategy to sensitize LMB-resistant
lung cancer cells by combining LMB and
doxorubicin (DOX). Among the different treatment regimens, pretreatment with DOX (pre-DOX) and subsequent treatment with LMB to A549 cells significantly decreased the 50% inhibitory concentration (IC50) as compared to that of LMB alone (4.4 nM vs. 10.6 nM, P<0.05). Analysis of cell cycle and apoptosis by flow cytometry further confirmed the cytotoxic data. To investigate molecular mechanisms for this
drug combination effects, p53 pathways were analyzed by Western blot, and nuclear
proteome was evaluated by two dimensional-difference gel electrophoresis (2D-DIGE) and mass spectrometry. In comparison with control groups, the levels of p53, phospho-p53 (ser15), and p21
proteins were significantly increased while phospho-p53 (Thr55) and
survivin were significantly decreased
after treatments of pre-DOX and LMB (P<0.05). The 2D-DIGE/MS analysis identified that sequestosome 1 (SQSTM1/p62) had a significant increase in pre-DOX and LMB-treated cells (P<0.05). In conclusion, our results suggest that
drug-resistant
lung cancer cells with p53 wild type could be sensitized to cell death by scheduled combination treatment of DOX and LMB through activating and restoring p53 as well as potentially other signaling pathway(s) involving sequestosome 1.