Induction of the Phase II Enzyme, Quinone Reductase, by Withanolides and Norwithanolides from Solanaceous Species

The induction of the phase II drug-metabolizing enzyme, NAD(P)H:quinone reductase (QR), using Hepa 1c1c7 hepatoma cells, is currently used as a key member of a panel of in vitro bioassays in our program directed towards the discovery of new plantderived cancer chemopreventive agents. Among a group of natural products, which have been studied as QR inducers are the withanolides, which constitutes about 400 C28 ergostane-type steroids found mainly in approximately 10 genera of the plant family Solanaceae. New withanolides have been isolated and characterized in our recent work on Physalis philadelphica (tomatillo), which is used as a vegetable and condiment in Mexican and Central American cuisine. A further study on Deprea subtriflora has led to the discovery of a new class of C-18 norwithanolides with only 27 carbons in their skeleton. Preliminary structure-activity relationships have been determined for the in vitro induction of QR by members of the withanolide and norwithanolide classes.