Background: We previously reported novel quinuclidinone analogs that showed both additive and synergistic cytotoxicity in lung cancer cells. We aimed at understanding the mechanism of these analogs and also their cytotoxic effect on normal cells. The effects of these analogs were studied in response to gamma radiation in H1299 human large cell lung carcinoma cells that are null for p53, normal lung epithelial cell line (NL-20) and H1299 cells stably transfected with p53.
Materials and methods: The effects of the analogs were investigated by MTT assay, clonogenic survival assay, sphingomylinase activity, Cox-2 activity, ELISA-based apoptotic assay, terminal deoxynucleotidyl transferase dUTP nick end labeling assay, immunofluoresence staining, flow cytometry, real-time reverse transcription polymerase chain reaction and Western blot analysis.
Results: Our data indicated that 8a and 8b reduced cell proliferation and induced apoptosis in H1299 cells more than H1299-wt p53 cells and NL-20 cells, they also radiosensitize H1299 cells to gamma radiation more than NL-20 cells. 8a and 8b decreased cells in G(2) phase in H1299 cells more than NL-20 cells, which is confirmed by increased expression of cyclin B in H1299 cells, with no significant increase in H1299-wtp53. 8a increased sphingomylinase activity and ceramide level in H1299 more than the rest of cells, it also reduced expression level and activity of COX-2 while it increased caspase-3 activity and induced PARP-1 cleavage. Both derivatives increased expression of p53 in H1299-wt p53 level, while they did not show significant increase in NL-20 cells. Interestingly, these analogs induced apoptosis in H1299 and p53 stably transfected H1299 cells, but they had less effect on normal lung epithelial cells (NL-20).
Conclusion: All these results confirm that our quinuclidinone derivatives provoke cytotoxicity in lung cancer cells more than normal cells, which is a feature not present in most chemotherapeutic drugs.