The eudesmanolide tanapsin from Tanacetum oshanahanii and its acetate induce cell death in human tumor cells through a mechanism dependent on reactive oxygen species.

In this study the cytotoxicities of two species of Tanacetum were evaluated against human tumor cells. Tanacetum oshanahanii extract was more cytotoxic than Tanacetum ptarmiciflorum. Analyses of both extracts of Tanacetum by ultrahigh performance liquid chromatography-tandem mass spectrometry revealed that T. oshanahanii extract contains the eudesmanolide tanapsin, while T. ptarmiciflorum lacks this sesquiterpene lactone. Tanapsin was cytotoxic against leukemia and melanoma cells, including cells that overexpress Bcl-2 and Bcl-xL, with IC50 values of approximately 10 µM, but not against quiescent or proliferating human peripheral blood mononuclear cells. Treatment of cells with tanapsin induced apoptosis. This was prevented by the non-specific caspase inhibitor z-VAD-fmk, and reduced by the selective caspase-3/7 inhibitor z-DEVD-fmk. Tanapsin acetate was also cytotoxic against leukemia and melanoma cells and a potent apoptotic inducer. Tanapsin-induced cell death was found to be associated with (i) the loss of inner mitochondrial membrane potential (ΔΨm) and release of mitochondrial cytochrome c, (ii) the activation of multiple caspases and the mitogen-activated protein kinase pathway, and (iii) an increase in reactive oxygen species generation. Generation of reactive oxygen species in response to tanapsin seems to play a crucial role in the cell death process since the antioxidant N-acetyl-l-cysteine blocked both ROS generation and cell death.

Ayanin diacetate-induced cell death is amplified by TRAIL in human leukemia cells.

Here we demonstrate that the semi-synthetic flavonoid ayanin diacetate induces cell death selectively in leukemia cells without affecting the proliferation of normal lymphocytes. Incubation of human leukemia cells with ayanin diacetate induced G(2)-M phase cell cycle arrest and apoptosis which was prevented by the non-specific caspase inhibitor z-VAD-fmk and reduced by the overexpression of Bcl-x(L). Ayanin diacetate-induced cell death was found to be associated with: (i) loss of inner mitochondrial membrane potential, (ii) the release of cytochrome c, (iii) the activation of multiple caspases, (iv) cleavage of poly(ADP-ribose) polymerase and (v) the up-regulation of death receptors for TRAIL, DR4 and DR5. Moreover, the combined treatment with ayanin diacetate and TRAIL amplified cell death, compared to single treatments. These results provide a basis for further exploring the potential applications of this combination for the treatment of cancer.

Melatonin decreases cell proliferation and induces melanogenesis in human melanoma SK-MEL-1 cells.

Melatonin is an indoleamine synthesized in the pineal gland, and after its release into the blood, it has an extensive repertoire of biological activities, including antitumoral properties. In this study, we found that melatonin reduced the growth of the human melanoma cells SK-MEL-1. The antiproliferative effect was associated with an alteration in the progression of the phases of the cell cycle and also with an increase in tyrosinase activity, the key regulatory enzyme of melanogenesis. Antagonists for melatonin membrane receptors (luzindole and 4-P-PDOT) and the general G-coupled receptor inhibitor, pertussis toxin, did not prevent the melatonin-induced cell growth arrest; this suggests a mechanism independent of G-coupled membrane receptors. In contrast, p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway seems to play a significant role in cell growth inhibition by melatonin. The indoleamine-induced phosphorylation of p38 MAPK and the effect on cell proliferation were abrogated by the specific inhibitor SB203580. Furthermore, comparative studies with known antioxidants such as N-acetyl-l-cysteine and trolox indicate that the growth of SK-MEL-1 cells is highly sensitive to antioxidants.

Naturally occurring asteriscunolide A induces apoptosis and activation of mitogen-activated protein kinase pathway in human tumor cell lines.

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.