Cancer chemopreventive agents discovered by activity-guided fractionation: An update

Further to a previous contribution to this journal (Kinghorn et al., Curr. Org. Chem. 1998, 2, 597), in the present review we describe a continuation of efforts to obtain novel potential cancer chemopreventive agents from mainly edible plants using selected in vitro bioassays to monitor chromatographic fractionation. Altogether, 52 further active compounds have been isolated from eight plant acquisitions, of which 19 are new natural products. Members of a total of eleven plant secondary metabolite classes have been isolated and characterized, namely, benzofuranoids, ceramides, flavonoids, lignans, a phenol, a porphyrin, sesquiterpenoids, stilbenoids, a stilbenolignan, triterpenoids, and withanolides. Several of these in vitro-active compounds have been found to be active in a follow-up mouse mammary organ culture model, and a number have been selected for more advanced biological testing. Examples include the withanolide, ixocarpalactone A, from the aerial parts of Physalis philadelphica, which has shown promising activity in a quinone reductase induction assay, and four flavonoid constituents from the whole plants of Broussonetia papyrifera, with potent aromatase inhibitory activity.