Inhibitors of the Oncogenic Transcription Factor AP-1 from Podocarpus latifolius

Abstract

An activator protein-1 (AP-1) based bioassay guided phytochemical investigation on Podocarpus latifolius led to the isolation of three new sempervirol type diterpenes, cycloinumakiol (1), inumakal (2), and inumakoic acid (3) along with three known norditerpenes (4-6). Compounds 4 and 6 were responsible for the observed bioactivity.Carcinogenesis, the process of transforming normal cells into cancer cells, is a multistage process of initiation, promotion, and progression. The activator protein-1 (AP-1), an oncogenic transcription factor, is a heterodimeric or homodimeric protein complex that is required for tumor promotion and progression. 1,2 The heterodimer AP-1 consists of Jun (cJun, Jun B and Jun D) paired with Fos (c-Fos, Fos B, Fra 1 and Fra 2) proteins; homodimers of Jun proteins also exist. 3 The N-terminally truncated c-Jun (TAM67) mutant protein has been shown to form homodimers or heterodimers with other Jun or Fos family members, which bind to AP-1 sequences, that subsequently demonstrate no or diminished AP-1 transactivation. 4 It has been shown that molecules that mimic TAM67 in inhibiting 12-Otetradecanoyl probol-13-ester (TPA)-stimulated AP-1 activity may be valuable for the prevention and treatment of cancers. 1,2 Hence, a search for novel and specific AP-1 inhibitors from natural products, including those of plant origin, might be beneficial for the prevention and therapy of cancer. We recently developed a high throughput assay to screen natural product extracts for such inhibitors. 2 An organic solvent extract of the root bark of Podocarpus latifolius (Thunb.) R.Br. ex Mirb. collected in Tanzania demonstrated activity in this assay and was subjected to bioassay-guided fractionation.Podocarpus is one of the most widely distributed genera of the family Podocarpaceae, with about 100 species having diverse morphology, ecology, and chemical constituents. A number of medicinal and non-medicinal ethnobotanical uses are reported for the genus Podocarpus. 5 Different biological activities such as cytotoxic, antibacterial, anti-∇ Dedicated to Dr. Koji Nakanishi of Columbia University for his pioneering work on bioactive natural products.* To whom correspondence should be addressed. Tel: 301-846-1942, Fax: 301-846-6177, beutlerj@mail.nih Podocarpus latifolius is a slow-growing evergreen tree which can reach a height of 30 m. The norditerpene dilactone macrophyllic acid and several biflavones have previously been reported from P. latifolius. 12 Our bioassay guided phytochemical investigation with respect to AP-1 led to the isolation of three new (1-3) and three known (4-6) diterpenes. Results and DiscussionThe fractionation of root bark extract (CH 2 Cl 2 -MeOH) of P. latifolius by successive diol and LH-20 column chromatography yielded three new (1-3) and three known (4-6) diterpenoids. Compound 1 was obtained as a reddish gum. The IR spectrum of 1 exhibited absorptions at 1601, and 1547 cm −1 due to oxymethylene and aromatic bonds, respectively. 13 The HREIMS analysis of 1 showed a molecular comp...

Coupling of Sterically Hindered Trisubstituted Olefins and Benzocyclobutenones by CC Activation: Total Synthesis and Structural Revision of Cycloinumakiol

“…Finally, hydrogenation of alkene 17 provided the proposed cycloinumakiol ( 1 ) in 88 % yield, the structure of which was unambiguously confirmed by 1 H/ 13 C NMR spectroscopy, HRMS, IR spectroscopy, and X‐ray crystallography. While we are confident about our structural characterization of 1 , unfortunately, the NMR spectra of synthetic cycloinumakiol do not match those reported in literature 2. Thus, we anticipated there was a structural misassignment for cycloinumakiol.…”

“…Previous biological studies of the extracts from the leaves of this plant revealed high antibiotic as well as anticancer activities resulting from inumakiols,1a totarols,1b and other norditerpenes (Figure 1). 1c,d Recently, guided by a bioassay based on activator protein‐1 (AP‐1), the investigation on extracts of podocarpus latifolius at the National Cancer Institute (NCI) led to the isolation of three new inumakiol‐family diterpenes, namely cycloinumakiol ( 1 ), inumakal ( 2 ), and inumakoic acid ( 3 ) 2. The proposed structure of cycloinumakiol ( 1 ) is clearly different from the rest of the tricyclic inumakiol‐family members.…”

“…The structure of 18 was also unambiguously confirmed by 1 H/ 13 C NMR spectroscopy, HRMS, IR spectroscopy, and X‐ray crystallography. Again, the NMR spectra of 18 do not match the reported data of cycloinumakiol 2. After careful analysis and comparison between ours and reported 1 H NMR data, we found a significant difference in chemical shifts of the C20‐methylene group: those of the natural sample are at 3.78 and 3.42 ppm, whereas those of the synthetic samples 1 and 18 are around 4.6 and 4.1 ppm, respectively.…”

Anticancer Activities and Mechanism of Action of Nagilactones, a Group of Terpenoid Lactones Isolated from Podocarpus Species

“…The mode of action of nagilactones is multifactorial, as it is frequently the case with natural products. It is not entirely elucidated, but several key pathways have been implicated in the antitumor activity of the most active compounds, essentially Nag-C, Nag-E and Nag-F. About ten years ago, it was shown that Nag-F was able to inhibit activation of the dimeric transcription factor AP-1 (activator protein 1) induced by the phorbol ester TPA (12-O-tetradecanoyl probol-13-ester), with a micromolar efficacy [44]. AP-1, which is in fact a group of transcription factors consisted of four sub-families (Jun, Fos, Maf, and the ATF-activating transcription factors), represents an important modulator in several immune disorders and carcinomas.…”

Rhodium‐Catalyzed Regioselective Carboacylation of Olefins: A CC Bond Activation Approach for Accessing Fused‐Ring Systems

“…The intramolecular insertion of olefins into the C1ÀC2 s bond of benzocyclobutenones would lead to benzofused tricycles (Scheme 2 b), which are key motifs in a number of biologically important natural products (Scheme 3). [21] However, there are a number of challenges: 1) achieving the desired regioselectivity is not trivial, because, in general, cleavage of the C1ÀC8 bond of benzocyclobutenones is kinetically favored and therefore catalyzed transformations that involve the cleavage of the C1 À C2 bond remain elusive; 2) the scope of olefins that can undergo carboacylation is often limited. [22] Herein, we describe the development of a rhodium-catalyzed regioselective olefin carboacylation reaction of benzocyclobutenones for rapid access to polyfused rings.…”