Cytotoxic 4-nerolidylcatechol from Pothomorphe peltata inhibits topoisomerase I activity

Bioactivity-guided fractionation of the leaf methanolic extract of P. pelta ta (Piperaceae), using the brine shrimp lethality test, led to the isolatio n of catechol derivative 4-nerolidylcatechol (4-NC). The methanolic extract was active against crown gall tumour in potato discs, showing a 22 % crown gall tumour inhibition (SD = 4%), while 4-NC was cytotoxic against KB tumo ur cells growth (EC50 = 1.3 mu g/ml). No interaction with DNA could be obse rved when tested using the methyl green-DNA (MG-DNA) bioassay. An inhibitio n in the activity of topoisomerase I using agarose gel electrophoresis was detected in the presence of the purified compound (IC50 = 20 mu g/ml), sugg esting that this could be a possible mechanism for the cytotoxicity observe d in KB cells.