## 4 Role of Triterpenoids in Cancer Prevention
### Role of Triterpenoids in Inflammation
PGs are endogenous mediators of inflammation and are formed from arachidonic acid by constitutive COX-1 and inducible COX-2. Production of higher levels of PGs is thought to cause cellular injury and ultimately lead to carcinogenesis by inhibiting apoptosis, stimulating cellular proliferation, and promoting angiogenesis and tumor invasiveness [159]. Cycloartane triterpenoids from _Cimcifuga dahurica_ suppressed the expression of cdc2 and COX-2 protein. These results imply that triterpenoids possess potential antitumor activities and exert their cytotoxicity through apoptosis and G2/M cell cycle arrest [146]. Many triterpenoids derived from botanical sources play an important role in reducing inflammation. These include avicin, asiatic acid, astragaloside, betulin, betulinic acid, boswellic acid, celastrol, cucurbitacin, diosgenin, erythrodiol, ganoderiol, ginsengosides, glycyrrhizin, glycyrrheinic acid, gypenoside, lupeol, madecassic acid, maslinic acid, oleandrin, oleanolic acid, platycodon D, pristimerin, saikosaponins, unsolic acid, and withanolide (Table 2). Many of these triterpenoids target NF-kB, leading to its downregulation. Pentacyclic triterpenoids have been found to have many functions, although their effective concentrations for various cellular effects may vary widely. Depending upon the dose administered, triterpenoids can induce anti-inflammatory, cytoprotective, tumor-differentiating, proliferation-arresting, and apoptotic effects [160, 161, 162]. The anticancer activities of triterpenoids appear to be mediated, at least in part, by their common ability to block TNF-induced NF-kB activation by inhibiting IKK\(\beta\)[163,164]. The synthetic triterpenoid 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl] imidazole (CDDO-Im) blocks NF-kB activation through direct inhibition of IKK\(\beta\)[35]. This is evident from the fact that the molecular targets of the synthetic oleanane triterpenoids include IKK and also pathways involving STAT, IL-6, TGF-\(\beta\), and KEAP1 (the inhibitor of the transcription factor Nrf2). Inhibition of multiple targets by triterpenoids is believed to be mediated by the promiscuous reversible Michael addition of these compounds to exposed nucleophilic groups (such as accessible cysteine sulfides) of various susceptible signaling proteins [165]. Triterpenoids affect multiple signaling pathways, and the clinical properties of triterpenoids,particularly those of pentacyclic triterpenoids, have been shown in various studies. The structure-activity relationships indicate that the presence of \(\alpha\),\(\beta\)-unsaturated carbonyl moieties significantly enhance the potency of these pentacyclic triterpenoids. Of the 12 pentacyclic triterpenoids, four (CDDO, CDDO-Me, pristimerin, and celastrol) have been shown to be potently and selectively lethal to different cancer cells and show a several fold increase in anti-inflammatory activity. This action is caused by the \(\alpha\),\(\beta\)-unsaturated carbonyl in ring A. The incorporation of a cyano and keto group within this enone moiety further enhances its efficacy and potency. Avicins are electrophilic pentacyclic triterpenoids with proapoptotic, anti-inflammatory, and antioxidant properties derived from _Acacia victoriae_. Avicins have been shown to induce redox-dependent post-translational modification of cysteine residues to regulate protein function, which downregulate both STAT3 activity and the expression of STAT3-regulated prosurvival proteins and contribute to the induction of apoptosis _in vitro_[166]. Avicins were found to be potent inhibitors of TNF-induced NF-\(\kappa\)B and to slow the accumulation of the p65 subunit of NF-\(\kappa\)B in the nucleus; however, the degradation of \(\mathrm{I}\kappa\)B\(\alpha\) was unaffected. In addition Avicins blocked the binding of NF-\(\kappa\)B to DNA in _in vitro_ binding assays.