BACKGROUND: Gamabufotalin (CS-6), a major bufadienolide of Chansu, has been used 
for cancer therapy due to its desirable metabolic stability and less adverse 
effect. However, the underlying mechanism of CS-6 involved in anti-tumor 
activity remains poorly understood.
METHODS: The biological functions of gamabufotalin (CS-6) were investigated by 
migration, colony formation and apoptosis assays in NSCLC cells. The nuclear 
localization and interaction between transcriptional co-activator p300 and NF-κB 
p50/p65 and their binding to COX-2 promoter were analyzed after treatment with 
CS-6. Molecular docking study was used to simulate the interaction of CS-6 with 
IKKβ. The in vivo anti-tumor efficacy of CS-6 was also analyzed in xenografts 
nude mice. Western blot was used to detect the protein expression level.
RESULTS: Gamabufotalin (CS-6) strongly suppressed COX-2 expression by inhibiting 
the phosphorylation of IKKβ via targeting the ATP-binding site, thereby 
abrogating NF-κB binding and p300 recruitment to COX-2 promoter. In addition, 
CS-6 induced apoptosis by activating the cytochrome c and caspase-dependent 
apoptotic pathway. Moreover, CS-6 markedly down-regulated the protein levels of 
COX-2 and phosphorylated p65 NF-κB in tumor tissues of the xenograft mice, and 
inhibited tumor weight and size.
CONCLUSIONS: Our study provides pharmacological evidence that CS-6 exhibits 
potential use in the treatment of COX-2-mediated diseases such as lung cancer.