Cinobufagin (
CBG) is a cardiotoxic bufanolide
steroid secreted by the skin and parotid
venom glands of the Asiatic toad Bufo bufo gargarizans (called
Chan-Su). Although
CBG is known to exhibit anti-
cancer activities, very little is known about its potential mechanism(s) of action. In this study, we investigated whether
CBG mediates its effect through the modulation of the
mitogen-activated protein kinases (MAPKs) signaling pathway in human
multiple myeloma (MM) U266 cells. We found that
CBG caused the significant activation of ERK, JNK and
p38 MAPK in U266 cells.
CBG showed much higher cytotoxicity against U266 cells as compared to peripheral blood mononuclear cells (PBMC). Induction of
CBG increased
reactive oxygen species (ROS) generation from mitochondria, which is associated with the induction of apoptosis as characterized by increased sub-G1
DNA contents of cell cycle, positive
Annexin V binding, activation of
caspase-3 and cleavage of PARP. Inhibition of ROS generation by
N-acetyl-l-cysteine (NAC) significantly prevented
CBG-induced ERK, JNK and
p38 MAPK activation and apoptosis.
CBG also down-regulated the expression of various downstream gene products that mediate cell proliferation, survival, angiogenesis and
metastasis. Interestingly, ERK, JNK and p38MAPK pharmacological inhibitors blocked
CBG-induced MAPKs activation and ERK inhibitor (
PD98059) also prevented the
CBG-induced
caspase-3 activation and PARP cleavage in U266 cells. Taken together, these findings suggest that
CBG can act as a potent
anticancer agent against MM and possibly exerts its effects through the ROS-mediated activation of ERK, JNK and
p38 MAPK leading to the activation of
caspase-3 in U266 cells.