Chlorinated Guaiane-Type Sesquiterpene Lactones as Cytotoxic Agents against Human Tumor Cells

Guaiane-type sesquiterpene lactones are naturally occurring compounds which have attracted attention due to their array of biological activities. In this study, chlorinated guaianolides - , isolated from plants of the genus , were evaluated against the human leukemia cell lines HL-60, U-937, a specific U-937 cell line that overexpresses the anti-apoptotic Bcl-2 protein and the human melanoma cell line SK-MEL-1. This established the relevant structure-growth inhibition relationships. Chlorohyssopifolins A ( ), C ( ) and D ( ) and linichlorin A ( ) were the most potent compounds in terms of inducing growth inhibition in the four cell lines. IC values were below 10 μM in all cases. Chlorohyssopifolins A ( ) and D ( ) and linichlorin A ( ) were potent apoptotic inducers in human U-937 leukemia cells, as determined by fluorescent microscopy and flow cytometry, and their mechanism of action was associated with cytochrome release, caspase activation and poly(ADP-ribose)polymerase cleavage. Overall this study shows that guaianolides induce cytotoxicity against human tumor cells and provides important insights into the cell death pathways that are involved.