Capsaicin inhibited the proliferation of human SCLC cells in a time- and concentration-dependent manner.

<p>(A) MTT assays show at the treatment of H69 and H82 cells with 50 µM capsaicin causes a decrease in cell viability starting from 24 hours to 72 hours. (B) The MTT assay was repeated in DMS53 and DMS114 cells. Similar results were obtained. (C) Capsaicin displays potent dose-dependent anti-proliferative activity in H69 human SCLC cells. H69 cells were serum-starved for 36 hours and then re-stimulated with 10% FBS for 18 hours in the presence or absence of the indicated doses of capsaicin. BrdU incorporation assays were performed to assess the anti-proliferative effects of capsaicin. (D) The experiment was repeated in H82, DMS114 and DMS53 human SCLC cell lines and similar results were obtained. Most interestingly, capsaicin displayed relatively little anti-proliferative activity in SAEC and NHBE normal lung epithelial cells, indicating that the anti-proliferative activity of capsaicin was specific for lung cancer cells. (E) The results obtained from the BrdU assays were verified by the measurement of PCNA levels in human SCLC cells. Capsaicin decreased the number of PCNA positive cells in all the four SCLC cell lines. (F) FACS analysis confirms that capsaicin causes G1/S arrest in H69 human SCLC cells. H69 cells were serum-starved for 36 hours and subsequently re-stimulated with 10% FBS for 18 hours (to induce S-phase entry) in the presence or absence of 50 µM capsaicin. Cells were then stained with propidium iodide and analyzed by FACS to quantitate the relative percentage of cells in G1 and S phase. The percentage of cells in G1 and S-phase of untreated cells were taken to be 100%, and the relative percentages of capsaicin-treated cells were calculated relative to the control. Capsaicin increased the percentage of cells in G1 phase and concomitantly decreased the percentage of cells in S-phase, indicating the presence of G1/S arrest in capsaicin-treated H69 cells. Values indicated by an “*” or a different letter are statistically significant.