Gordon W. Gribble

Pharmacodynamic characterization of chemopreventive triterpenoids as exceptionally potent inducers of Nrf2-regulated genes

Synthetic triterpenoids have been developed, which are potent inducers of cytoprotective enzymes and inhibitors of inflammation, greatly improving on the weak activity of naturally occurring triterpenoids. An imidazolide triterpenoid derivative, 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Im or TP235), has been previously shown to potently protect against hepatic tumorigenesis, acting in part by inducing cytoprotective genes through Keap1-Nrf2-antioxidant response element (ARE) signaling. In these studies, the pharmacodynamic activity of CDDO-Im is characterized in two distinct lines of ARE reporter mice and by measuring increases in Nqo1 transcript levels as a marker of cytoprotective gene induction. Oral administration of CDDO-Im induces ARE-regulated cytoprotective genes in many tissues in the mouse, including liver, lung, kidney, intestines, brain, heart, thymus, and salivary gland. CDDO-Im induces Nqo1 RNA transcripts in some organs at doses as low as 0.3 μmol/kg body weight (orally). A structure activity evaluation of 15 additional triterpenoids (a) confirmed the importance of Michael acceptor groups on both the A and C rings, (b) showed the requirement for a nitrile group at C-2 of the A ring, and (c) indicated that substituents at C-17 dramatically affected pharmacodynamic action in vivo. In addition to CDDO-Im, other triterpenoids, particularly the methyl ester CDDO-Me (TP155) and the dinitrile TP225, are extremely potent inducers of cytoprotective genes in mouse liver, lung, small intestine mucosa, and cerebral cortex. This pharmacodynamic characterization highlights the chemopreventive promise of several synthetic triterpenoids in multiple target organs. [Mol Cancer Ther 2007;6(1):154–62]

The synthetic triterpenoids CDDO-methyl ester and CDDO-ethyl amide prevent lung cancer induced by vinyl carbamate in A/J mice.

We report the first use of new synthetic triterpenoids to prevent lung cancer in experimental animals. Female A/J mice were treated with the mutagenic carcinogen vinyl carbamate, which induces adenocarcinoma of the lung in all animals within 16 weeks. If mice were fed either the methyl ester or the ethyl amide derivative of the synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO-ME and CDDO-EA, respectively), beginning 1 week after dosing with carcinogen, the number, size, and severity of lung carcinomas were markedly reduced. The mechanisms of action of CDDO-ME and CDDO-EA that are germane to these in vivo findings are the following results shown here in cell culture: (a) suppression of the ability of IFN-gamma to induce de novo formation of nitric oxide synthase in a macrophage-like cell line RAW264.7, (b) induction of heme oxygenase-1 in these RAW cells, and (c) suppression of phosphorylation of the transcription factor signal transducers and activators of transcription 3 as well as induction of apoptosis in human lung cancer cell lines.

Novel semisynthetic analogues of betulinic acid with diverse cytoprotective, antiproliferative, and proapoptotic activities.

Betulinic acid (BA), a pentacyclic triterpene isolated from birch bark and other plants, selectively inhibits the growth of human cancer cell lines. However, the poor potency of BA hinders its clinical development, despite a lack of toxicity in animal studies even at high concentrations. Here, we describe six BA derivatives that are markedly more potent than BA for inhibiting inducible nitric oxide synthase, activating phase 2 cytoprotective enzymes, and inducing apoptosis in cancer cells and in Bax/Bak−/− fibroblasts, which lack two key proteins involved in the intrinsic, mitochondrial-dependent apoptotic pathway. Notably, adding a cyano-enone functionality in the A ring of BA enhanced its cytoprotective properties, but replacing the cyano group with a methoxycarbonyl strikingly increased potency in the apoptosis assays. Higher plasma and tissue levels were obtained with the new BA analogues, especially CBA-Im [1-(2-cyano-3-oxolupa-1,20(29)-dien-28-oyl)imidazole], compared with BA itself and at concentrations that were active in vitro. These results suggest that BA is a useful platform for drug development, and the enhanced potency and varied biological activities of CBA-Im make it a promising candidate for further chemoprevention or chemotherapeutic studies. [Mol Cancer Ther 2007;6(7):2113–9]

Convenient Synthesis of Bis(3‐indolyl)‐acetylene via Sonogashira Coupling

Abstract We describe the synthesis of bis(3‐indolyl)acetylene 6 via a Pd‐catalyzed cross‐coupling reaction of iodoindole 8 and 3‐indolylacetylene 9, followed by deprotection of 14 to furnish 6.