Inhibition of hypoxia inducible factor-2 transcription: isolation of active modulators from marine sponges.

Renal or kidney cancer accounts for about 3% of all cancer cases reported each year in the U.S. Molecular signatures that define the cancer, such as the loss of functional VHL, are found in both sporadic and familial cases of cancer. In clear cell renal cancer, the transcription factor HIF-2α has been shown to have a distinct role in tumorigenesis. Our laboratories developed a cell-based screen to identify modulators of HIF-2α. Screening of the NCI's Natural Product Extract Repository resulted in the identification of 10 sponge extracts, from which 12 compounds were isolated. The biological evaluation of these compounds will be discussed including evaluation of HIF-1α vs HIF-2α selectivity and the isolated compounds' effects on mRNA from several pathways regulated by HIF.

Flabelliferins A and B, sesterterpenoids from the South Pacific sponge Carteriospongia flabellifera.

Two new sesterterpenoids named flabelliferins A (1) and B (2) were isolated from the lipophilic extract of the sponge Cateriospongia flabellifera, collected in the South Pacific near Vanuatu. The structure and absolute configuration of these two compounds were assigned by a combination of one- and two-dimensional NMR spectroscopy and by Mosher's ester analysis. Flabelliferin A (1) has a rare 25-homocheilanthane carbon skeleton, while flabelliferin B (2) is a 24-nor-25-homoscalarane sesterterpenoid.

Nothospondin, a new AP-1 inhibitory quassinoid from the Cameroonian plant Nothospondias staudtii.

A high throughput screen for inhibitors of the oncogenic transcription factor activator protein-1 (AP-1) was applied to the NCI repository of natural product extracts. The liphophilic extract of the plant Nothospondias staudtii (Simaroubaceae) displayed significant AP-1 inhibition. Bioassay-guided fractionation of the extract lead to a new quassinoid named nothospondin (1), and the known compound glaucarubinone (2). The structure of 1 was elucidated by spectroscopic methods. Compounds 1 and 2 showed potent, dose-dependent AP-1 inhibition at noncytotoxic concentrations.

Palmerolide macrolides from the Antarctic tunicate Synoicum adareanum.

Palmerolides D-G are new bioactive macrolides isolated from the Antarctic tunicate Synoicum adareanum and are related to the melanoma-selective cytotoxin palmerolide A. Most of these palmerolides are potent V-ATPase inhibitors and have sub-micromolar activity against melanoma. Though palmerolide A remains the most potent of this series of natural products against mammalian V-ATPase, recent data suggests that palmerolide D is the most potent against melanoma. A comparison of the bioactivity data obtained for these natural product palmerolides has provided insight into the substructures necessary to retain V-ATPase inhibition and cytotoxic activity.

Flavonoids from eight tropical plant species that inhibit the multidrug resistance transporter ABCG2.

Overexpression of ABCG2, a membrane-bound multi-drug transporter, can make tumor cells resistant to treatment with conventional chemotherapeutic agents. A high-throughput screening effort with the NCI repository of natural product extracts revealed that eight tropical plant extracts significantly inhibited the function of ABCG2. This activity was tracked throughout the extract fractionation process to a series of ABCG2 inhibitory flavonoids (1-13). Their structures were identified by a combination of NMR, mass spectrometry, and circular dichroism studies, and this resulted in the elucidation of (2S)-5,7,3'-trihydroxy-4'-methoxy-8-(3''-methylbut-2''-enyl)-flavonone (1), (2S)-5,7,3',5'-tetrahydroxy-8-[3'',8''-dimethylocta-2''(E),7''-dienyl]flavonone (3), and 5,7,3'-trihydroxy-3,5'-dimethoxy-2'-(3'-methylbut-2-enyl)flavone (12) as new compounds.

Palmadorins A--C, diterpene glycerides from the antarctic nudibranch Austrodoris kerguelenensis.

The nudibranch Austrodoris kerguelenensis is distributed widely around the Antarctic coast and continental shelves. Earlier collections from McMurdo Sound and the Weddell Sea shelf have afforded a suite of diterpene glyceride esters, a compound class implicated as a chemical defense in nudibranchs. The present chemical investigation of A. kerguelenensis collected near Palmer Station on the Western Antarctic Peninsula has revealed additional examples, palmadorins A-C (1-3), as the first three members of a new series of clerodane diterpenes. In this paper we describe their isolation, structure elucidation, and stereochemical analysis using a combination of one- and two-dimensional NMR spectroscopy and wet chemical methods.

Non-nutritive functional agents in rattan-shoots, a food consumed by native people in the Philippines.

The tender shoots of Calamus ornatus, one of the food items consumed by the native people, Kanawan Aytas, in the Bataan region of the Philippines, have not been studied before. A bioassay-guided investigation of its methanolic extract afforded non-nutritive functional agents (NFAs), steroidal saponins 1-3, along with its aglycone (4). The NFAs 1-4 inhibited cyclooxygenase enzymes, COX-1 and -2, by 47%, 43%, 33%, and 53% and 71%, 75%, 78%, and 73%, respectively, at 28.2, 24.2, 21.2 and 60.4µM. Treatment of breast (MCF-7), CNS (SF-268), lung (NCI-H460), colon (HCT-116) and gastric (AGS) cancer cell lines with the extract at 100µg/ml reduced cell proliferation. Similarly, the pure NFAs 2 and 3 reduced the cell viability of breast, CNS, lung, colon and gastric cancer cell lines by 37.5%, 22.4%, 53.3%, 58.2%, 40.3% and 29.8%, 21.3%, 45.6%, 37.1%, 25.0%, respectively, at 24.2 and 21.2µM. The 50% reduction in cell viability (IC50) concentrations of 2 and 3 against these cancer cell lines were 8.8, 6.1, 7.5, 23.8, 12.1 and 3.8, 7.1, 3.3, 14.3, 12.1µM, respectively. This is the first report on the isolation of steroidal saponins from C. ornatus shoots and their antiinflammatory and tumor cell proliferation inhibitory activities. Therefore, our results suggest that the Kanawan Aytas may yield health benefits from rattan-shoots in their diet.

Ecdysteroids from the Antarctic tunicate Synoicum adareanum.

Five new ecdysteroids, hyousterones A-D (2-5) and abeohyousterone (6), have been isolated from the Antarctic tunicate Synoicum adareanum along with the known ecdysteroid diaulusterol B (1). Hyousterones B (3) and D (5) are unusual ecdysteroids in bearing the 14beta-hydroxyl group, and abeohyousterone incorporates the 13(14-->8) abeo steroid skeleton, reflecting a rearrangement of the steroid C/D ring system. Abeohyousterone has moderate cytotoxicity toward several cancer cell lines. Hyousterones bearing the 14alpha-hydroxy group (2 and 4) were weakly cytotoxic, while the 14beta-hydroxy hyousterones (3 and 5) were devoid of cytotoxicity. The 14beta-hydroxy function may be a thermodynamic pathway to the 13(14-->8) abeo steroid skeleton. Hyousterones, abeohyousterone, and diaulusterol B are the first ecdysteroids reported from tunicates.

Palmerolide A, a cytotoxic macrolide from the antarctic tunicate Synoicum adareanum.

Palmerolide A, a 20-membered macrocyclic polyketide bearing carbamate and vinyl amide functionality, was isolated from the tunicate Synoicum adareanum collected from the vicinity of Palmer Station on the Antarctic Peninsula. Palmerolide A displays potent and selective cytotoxicity toward melanoma (UACC-66 LC50 = 0.018 muM) and appears to operate via inhibition (IC50 = 2 nM) of V-ATPase.

Chemical investigation of predator-deterred macroalgae from the Antarctic peninsula.

Chemical investigation of five Antarctic macroalgae whose tissues and crude extracts displayed ecologically relevant feeding deterrence in field bioassays was performed. Eleven compounds were characterized from the three red algae studied, of which four (1-3 and 9) were previously unreported, and four compounds were found from two brown algae, two (12 and 14) of which are new natural products. Several of these pure compounds have been individually investigated in ecological and/or pharmacological bioassays.