Possible role of nitric oxide in taxol induced apoptosis in lung cancer cell line

Purpose. The role of nitric oxide (NO) in cell death (apoptosis) was investigated in human lung cancer cell line A549 and its taxol resistant sub-clone, A549-T24. - It has been shown that NO generated by eNOS plays an anti-apoptotic role in normal cells in response to pro-apoptotic stimuli such as TNF-á. Conversely, a number of reports indicate that NO generated by iNOS promotes tumor cell apoptosis. The aim of this study was to determine whether taxol induced apoptosis in human lung cancer cell lines is associated with altered expression of eNOS and iNOS. Methods. The cells were culture in DMEM F-12media containing fetal bovine serum. The mRNA levels of iNOS and eNOS were measured by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR), using 18S rRNA as an internal standard. NO was measured with a Clark-type electrode (ISO-NO). Results. RT-PCR indicated that iNOS mRNA expression was significantly up-regulated in taxol treated A549 cells compared with that in the control. However, iNOS expression was absent in the drug resistant sub-clone. Accordingly, electrochemical measurement of NO concentration revealed a higher level of NO in taxol treated A549 cells. The taxol induced apoptosis was correlated with increased iNOS expression and subsequent increase in NO level. In contrast, the drug resistant cell line expressed higher eNOS mRNA compared to their drug sensitive counterpart. Furthermore, taxol treatment resulted in significant reduction in eNOS mRNA expression in the drug sensitive cell line. Conclusion. The findings that iNOS expression is 1) significantly elevated in the taxol treated A549 cells and 2) absent in resistant cell line, suggests that taxol induced apoptosis is partly regulated by NO resulting from iNOS mRNA expression. Taken together, these results indicate that down-regulation of iNOS may contribute to the development of chemoresistance. (Supported in part by the Holmok Cancer Research Fund and Artistic Activity Grant at University of the Pacific