Cytotoxicity of the Sesquiterpene Lactone Spiciformin and Its Acetyl Derivative against the Human Leukemia Cell Lines U-937 and HL-60.

Spiciformin (1) is a sesquiterpene lactone with a germacrane skeleton that is found in two Tanacetum species endemic to the Canary Islands. In this study, the cytotoxicities of 1 and its acetyl derivative (2) were evaluated against human tumor cells. These sesquiterpene lactones were cytotoxic against human acute myeloid leukemia (U-937 and HL-60) cells, even in cells over-expressing the pro-survival protein Bcl-2, but melanoma (SK-MEL-1) and human mononuclear cells isolated from blood of healthy donors were more resistant. Both compounds are apoptotic inducers in human leukemia U-937 cells. Cell death was mediated by the processing and activation of initiator and effector caspases and the cleavage of poly(ADP-ribose) polymerase, and it was blocked by a broad-spectrum caspase inhibitor and (in the case of sesquiterpene lactone 2) by the selective caspase-3/7, -8, and -9 inhibitors. In addition, certainly in the case of compound 2, this was found to be associated with a decrease in mitochondrial membrane potential, downregulation of the anti-apoptotic protein Bcl-2, activation of the mitogen-activated protein kinases signaling pathway, and generation of reactive oxygen species. It will, therefore, be relevant to continue characterization of this class of compounds.

3'-Hydroxy-3,4'-dimethoxyflavone blocks tubulin polymerization and is a potent apoptotic inducer in human SK-MEL-1 melanoma cells.

Flavonoids are naturally occurring polyphenolic compounds and are among the most promising anticancer agents. A series of flavonols and their 3-methyl ether derivatives were synthesized and assessed for cytotoxicity. It was found that 3'-hydroxy-3,4'-dimethoxyflavone (flavonoid 7a) displayed strong cytotoxicity against human SK-MEL-1 melanoma cells and blocked tubulin polymerization, but had no significant cytotoxic effects against quiescent or proliferating human peripheral blood mononuclear cells. Our analyses showed that flavonoid 7a induces G2-M cell cycle arrest and apoptosis in melanoma cells which is associated with cytochrome c release and activation of both extrinsic and intrinsic apoptotic pathways of cell death.

Antiproliferative activity and apoptosis induction by 3',4'-dibenzyloxyflavonol on human leukemia cells.

In this study, we investigated the effects of synthetic 3',4'-dibenzyloxyflavonol on viabilities of eight human tumor cells. It was cytotoxic against leukemia cells (HL-60, U-937, MOLT-3, K-562, NALM-6, Raji), with significant effects against P-glycoprotein-overexpressing K-562/ADR and Bcl-2-overexpressing U-937/Bcl-2 cells, but had no significant cytotoxic effects against quiescent or proliferating human peripheral blood mononuclear cells. The IC50 value for the leukemia HL-60 cells was 0.8 ± 0.1 µM. This indicates a 60-fold greater toxicity than the naturally occurring flavonol quercetin. Synthetic 3',4'-dibenzyloxyflavonol induced S phase cell cycle arrest and was a potent apoptotic inducer in human leukemia cells. Cell death was (i) mediated by the activation and the cleavage of initiator and executioner caspases; (ii) prevented by the pan-caspase inhibitor z-VAD-fmk; (iii) associated with the release of cytochrome c and with the phosphorylation of members of the mitogen activated protein kinases including p38MAPK, JNK/SAPK and ERK, and (iv) independent of the generation of reactive oxygen species. The synthetic 3',4'-dibenzyloxyflavonol is a potent cytotoxic compound against several human leukemia cells and might be useful in the development of new strategies in the fight against cancer.