Enhancement of sensitivity to tumor necrosis factor alpha in non-small cell lung cancer cells with acquired resistance to gefitinib.

Tumor cells that have acquired resistance to gefitinib through continuous drug administration may complicate future treatment. To investigate the mechanisms of acquired resistance, we established PC-9/ZD2001, a non-small-cell lung cancer cell line resistant to gefitinib, by continuous exposure of the parental cell line PC-9 to gefitinib. After 6 months of culture in gefitinib-free conditions, PC-9/ZD2001 cells reacquired sensitivity to gefitinib and were established as a revertant cell line, PC-9/ZD2001R. PC-9/ZD2001 cells showed collateral sensitivity to several anticancer drugs (vinorelbine, paclitaxel, camptothecin, and 5-fluorouracil) and to tumor necrosis factor alpha (TNF-alpha). Compared with PC-9 cells, PC-9/ZD2001 cells were 67-fold more sensitive to TNF-alpha and PC-9/ZD2001R cells were 1.3-fold more sensitive. Therefore, collateral sensitivity to TNF-alpha was correlated with gefitinib resistance. PC-9/ZD2001 cells expressed a lower level of epidermal growth factor receptor (EGFR) than did PC-9 cells; this down-regulation was partially reversed in PC-9/ZD2001R cells. TNF-alpha-induced autophosphorylation of EGFR (cross-talk signaling) was detected in all three cell lines. However, TNF-alpha-induced Akt phosphorylation and IkappaB degradation were observed much less often in PC-9/ZD2001 cells than in PC-9 cells or PC-9/ZD2001R cells. Expression of the inhibitor of apoptosis proteins c-IAP1 and c-IAP2 was induced by TNF-alpha in PC-9 and PC-9/ZD2001R cells but not in PC-9/ZD2001 cells. This weak effect of EGFR on Akt pathway might contribute to the TNF-alpha sensitivity of PC-9/ZD2001 cells. These results suggest that therapy with TNF-alpha would be effective in some cases of non-small-cell lung cancer that have acquired resistance to gefitinib.