Triterpenoids and sesquiterpenoids for prostate cancer therapy

Several classes of natural products and their derivatives play a pivotal role as anticancer agents. One important class of natural compounds, terpenoids, can be broadly classifi ed into monoterpenoid

(10 carbon atoms), e.g., limonene, a-pinene, perillyl alcohol; sesquiterpenoid (15 carbon atoms) (Figure 4.1), e.g., parthenolide, zerumbone, artemisinin, costunolide, helenalin A; diterpenoid (20 carbon atoms), e.g., triptolide, acanthoic acid, tashinone IIA; triterpenoids/steroids (30 carbon atoms) (Figure 4.2), e.g., ursolic acid, oleanolic acid, betulinic acid, celastrol; and tetraterpenoids/ carotenoids (40 carbon atoms), e.g., lycopene, astaxanthin. Sesquiterpenoids are naturally occurring 15-carbon compounds containing 3 isoprenoid units and are commonly found in a wide variety of plants, microorganisms, and marine life (Connolly and Hill, 2010; Shanmugam, et al., 2011a; Shanmugam, et al., 2012a). Sesquiterpenoids are classified according to the ring numbering system and the functional groups in the core structures such as acyclic, monocyclic, bicyclic, or tricyclic sesquiterpenoids (Chen, et al., 2011). These terpenoids have been shown to exhibit anti-inflammatory, anti-microbial, and anti-cancer activities (Bishayee, et al., 2011; Chen, et al., 2011; Petronelli, et al., 2009; Yadav, et al., 2010). In general, sesquiterpenoids have been shown to have cytotoxic activity against leukemia, breast, colon, lung, and liver cancer cells. However, sesquiterpenoids have shown exceptional prostate cancer specificity, and some of these compounds have been tested in human clinical trials (Chen, et al., 2011).