Abstract
Lung cancer, the leading cause of cancer‐related deaths in both men and women, is the consequence of disordered apoptosis, induction of which may have therapeutic utility. Hyperthermia has been identified as a stimulus for apoptosis. We investigated the mechanism of hyperthermia‐induced cell death in ras‐transformed lung cells. Effect of hyperthermia (43°C for 180 min) was compared between two cell lines, an immortalized (sv‐40) normal human bronchial epithelial (BEAS2‐B) and its malignant transformed (H‐ras transfected) counterpart (BZR‐T33). Survival after hyperthermia: 7‐d growth culture BEAS2‐B, 1.03 ± 0.007 and BZR‐T33, 0.39 ± 0.008 (P < 0.05); clonogenic assays BEAS2‐B, 0.76 ± 0.003 and BZR‐T33, 0.41 ± 0.004 (P < 0.05). Hoechst positive (apoptotic) cells: BEAS2‐B, 11 ± 3% and BZR‐T33, 78 ± 5% (P < 0.05). TUNEL, DNA fragmentation, and Annexin‐V all corroborate this result. Western blot comparing the effect of hyperthermia in BZR‐T33 cells to BEAS2‐B cells revealed: TRAIL and FAS‐L displayed significant increases (threefold and twofold, respectively); caspase‐3 showed a decrease in uncleaved form and an increase in cleaved form, and a 50‐fold increase in activity effectively blocked with the caspase‐3 inhibitor DEVD‐fmk; caspase‐9 showed near depletion of uncleaved; poly (ADP‐ribose) polymerase (PARP) degradation was clearly visible during heating. After hyperthermia, gene expression demonstrates a 5.7‐fold increase in TRAIL and insignificant changes in tumor necrosis factor‐α (TNF‐α), FAS‐L, and caspases 3, 8, 9 in transformed cells. Data demonstrated that hyperthermia induces apoptosis in transformed cells, and that apoptosis is mediated by caspase‐3 as a result of activation of cell‐death membrane receptors of the tumor‐necrosis‐factor family. In summary, these data suggest that hyperthermia could become an additional modality in the multidisciplinary approach to the treatment of lung cancer. © 2005 Wiley‐Liss, Inc.