Inhibiting NF-kappaB Activation by Triptolide Enhances TRAIL-induced Cell Death in Lung Cancer Cells

Kim, Youn Seup; Park, Jae Seuk; Jee, Young Koo; Lee, Kye Young

Abstract

PURPOSE: High frequency of p53 mutations in lung cancer is a major obstacle to chemotherapy-induced apoptosis because p53 is known to play an important role as a final translator for cancer apoptosis. Members of the TNF family have potential as anti-tumor agents because they induce apoptosis regardless of the p53 phenotype. Despite these advantages, the clinical utility of both TNF-alpha and FasL has been hampered by toxic side effects including NF-kappaB activation leading to septic shock and lethal hepatocyte apoptosis respectively. TRAIL (TNF-related apoptosis-inducing ligand), or Apo2L (Apo2 ligand) is a newly identified member of the family which appears to be tumor-selective and less toxic to the normal cells owing to distinct decoy receptor expression. Recently, it was described that TRAIL also can activate NF-kappaB which is a well-known anti-apoptotic transcriptional factor.
MATERIALS AND METHODS
We found that TRAIL activates NF-kappaB in A549 (wt p53) and NCI-H1299 (null p53) lung cancer cells by luciferase reporter gene assay and electromobility shift assay. We set out to identify an agent that would sensitize lung cancer cells to TRAIL-induced apoptosis through inhibition of NF-kappaB activation.
RESULTS
We found that triptolide, an oxygenated diterpene extracted and purified from the Chinese herb Tripterygium wilfordii sensitized A549 and NCI-H1299 cells to TRAIL-induced apoptosis through inhibition of NF-kappaB activation. Pretreatment with MG132 which is a well-known NF-kappaB inhibitor by blocking degradation of IkappaBalpha also greatly sensitized lung cancer cells to TRAIL-induced apoptosis. Triptolide did not block DNA binding of NF-kappaB activated by TRAIL as in the case of TNF-alpha. It has been already proven that triptolide blocks transactivation of p65 which plays a key role in NF-kappaB activation.
CONCLUSION
These observations suggest that triptolide may be a potentially useful drug to enhance TRAIL-induced tumor killing in lung cancer.