Topoisomerase I inhibition and cytotoxicity of licochalcones A and E from Glycyrrhiza inflata.

Licochalcones A (1) and E (2), retrochalcones or reversely constructed chalcones, isolated from the roots of Glycyrrhiza inflata, were evaluated for their cytotoxicities against four different human tumor cell lines; A549 (lung), SK-OV-3 (ovarian), SK-MEL-2 (melanoma) and HCT-15 (colon), using the sulforhodamine B (SRB) assay. The effects of these compounds toward the DNA topoisomerase I (topo I) inhibitory activity were also measured using the supercoiled DNA unwinding assay. All compounds showed moderate cytotoxicities against the four different human tumor cell lines and inhibited the topo I activity in dose-dependent manners. The inhibition of topo I by licochalcones A (1) and E (2) may explain the cytotoxicities of these compounds against the human tumor cell lines.