Sesquiterpene lactones have attracted much attention because they display a wide range of
biological activities, including antitumor properties. Here, we show the effects of the naturally occurring
sesquiterpene lactone asteriscunolide A (AS) on viability of human
melanoma,
leukemia and cells that overexpress antiapoptotic
proteins, namely Bcl-2 and Bcl-x(L). All cell lines were sensitive to this compound, with IC(50) values of approximately 5 microM. The cytotoxic effects of AS were accompanied by a G(2)-M phase arrest of the cell cycle and a concentration- and time-dependent appearance of apoptosis as determined by DNA fragmentation, translocation of
phosphatidylserine to the cell surface and sub-G(1) ratio. Apoptosis was associated with
caspase-3 activity and
poly(ADP-ribose) polymerase cleavage and was prevented by the nonspecific
caspase inhibitor
z-VAD-fmk, indicating that
caspases are essential components in this pathway. The apoptotic effect of AS was also associated with (i) the release of
cytochrome c from mitochondria which was accompanied by dissipation of the mitochondrial membrane potential (Delta Psi(m)) and (ii) the activation of the
mitogen-activated protein kinases (MAPKs) pathway. AS-induced cell death was potentiated by inhibition of
extracellular signal-regulated kinases (ERK) 1/2 signaling with
U0126 and
PD98059. Intracellular
reactive oxygen species (ROS) seem to play a pivotal role in this process since high levels of ROS were produced early (1 h) and apoptosis was completely blocked by the
free radical scavenger N-acetyl-L-cysteine (NAC). The present study demonstrates that AS-induced cell death is mediated by an intrinsic-dependent apoptotic event involving mitochondria and MAPKs, and through a mechanism dependent on ROS generation.