Kazuyo Ukai

Leucettamol A : A new inhibitor of Ubc13-Uev1A interaction isolated from a marine sponge, Leucetta aff. microrhaphis

A compound that inhibits the formation of a complex composed of the ubiquitin E2 enzyme Ubc13 and Uev1A was isolated from the marine sponge Leucetta aff. microrhaphis. The compound was identified as leucettamol A (1) by spectroscopic analysis. Its inhibition of Ubc13-Uev1A interaction was tested by the ELISA method, revealing an IC(50) value of 50 microg/mL. The compound is the first inhibitor of Ubc13-Uev1A interaction, that is, that of the E2 activity of Ubc13. Such inhibitors are presumed to be leads for anti-cancer agents that upregulate activity of the tumor suppressor p53 protein. Interestingly, hydrogenation of 1 increased its inhibitory activity with an IC(50) value of 4 microg/mL, while its tetraacetate derivative was inactive, indicating that the hydroxy and/or amino groups of 1 are required for the inhibition.

Verruculides A and B, two new protein tyrosine phosphatase 1B inhibitors from an Indonesian ascidian-derived Penicillium verruculosum.

Two new merosesquiterpenes, verruculides A (1) and B (2), were isolated from a culture broth of the Indonesian ascidian-derived Penicillium verruculosum TPU1311, together with three known congeners, chrodrimanins A (3), B (4), and H (5). The structures of 1 and 2 were assigned on the basis of their spectroscopic data (1D and 2D NMR, HRMS, UV, CD, and IR). Compound 2 had a linear sesquiterpene moiety and was considered to be the derivative of the biosynthetic precursor for 1 and 3-5. Compounds 1, 3, and 5 inhibited the activity of protein tyrosine phosphatase 1B (PTP1B) with IC50 values of 8.4, 8.5, and 14.9 μM, respectively. Compound 2 showed 40% inhibition at 23.1 μM, while 4 was not active at 20.7 μM.

Four new macrocyclic trichothecenes from two strains of marine-derived fungi of the genus Myrothecium

Three new macrocyclic trichothecenes, named 12′-hydroxyroridin E (1), roridin Q (2), and 2′,3′-deoxyroritoxin D (3), were isolated from the marine-derived fungus Myrothecium roridum TUF 98F42, and a new macrocyclic trichothecene, named roridin R (4), was isolated from Myrothecium sp. TUF 02F6 together with roridins A and H and isororidin E. The structures of new compounds were determined on the basis of their spectral data. Compound 2 possessed a unique ether moiety at the 13′ position of 1. Compound 4 was a 2′,3′-dihydro-2′-hydroxy derivative of roridin H. The IC50 values of compounds 1, 2, and 4 against the murine leukemia cell line L1210 were 0.19, 31.2, and 0.45 μM, respectively. Compound 3 showed antiyeast activity to Saccharomyces cerevisiae at 1 μg/disc (inhibition zone: 12.2 mm), which was about 10 time more active than roritoxin D (10.2 mm at 10 μg/disc).

Tetrahydrobostrycin and 1-Deoxytetrahydrobostrycin, Two New Hexahydroanthrone Derivatives, from a Marine-derived Fungus Aspergillus sp.

Two new hexahydroanthrones, tetrahydrobostrycin (1) and 1-deoxytetrahydrobostrycin (2), were isolated from a marine-derived fungus Aspergillus sp. strain 05F16 collected at the coral reef of Manado, Indonesia, together with bostrycin and abscisic acid. The structures of new compounds were determined on the basis of their spectral data. Compound 1 showed weak antibacterial activity against Staphylococcus aureus and Escherichia coli and 2 against S. aureus.

Structures and Biological Evaluations of Agelasines Isolated from the Okinawan Marine Sponge Agelas nakamurai.

Three new N-methyladenine-containing diterpenes, 2-oxoagelasines A (1) and F (2) and 10-hydro-9-hydroxyagelasine F (3), were isolated from the Okinawan marine sponge Agelas nakamurai Hoshino together with eight known agelasine derivatives, 2-oxoagelasine B (4), agelasines A (5), B (6), D (7), E (8), F (9), and G (10), and ageline B (11). The structures of 1-3 were assigned on the basis of their spectroscopic data and their comparison with those of the literature. Compounds 3 and 5-11 inhibited the growth of Mycobacterium smegmatis with inhibition zones of 10, 14, 15, 18, 14, 20, 12, and 12 mm at 20 μg/disc, respectively. All compounds were inactive (IC50 > 10 μM) against Huh-7 (hepatoma) and EJ-1 (bladder carcinoma) human cancer cell lines. Three 2-oxo derivatives (1, 2, and 4) exhibited markedly reduced biological activity against M. smegmatis. Moreover, compound 10 inhibited protein tyrosine phosphatase 1B (PTP1B) activity with an IC50 value of 15 μM.

Euryspongins A-C, three new unique sesquiterpenes from a marine sponge Euryspongia sp.

Three new unique sesquiterpenes, euryspongins A-C (1-3), were isolated from a marine sponge Euryspongia sp. collected at Iriomote Island, Okinawa, Japan. Compound 1 possessed a bicyclic furanosesquiterpene structure with six- and eight-membered rings, whereas compounds 2 and 3 had an α,β-unsaturated-γ-lactone ring instead of the furan ring in 1. Only five natural products in this class have been reported, and compounds 1-3 are the sixth-eighth examples of natural products. Compounds 1-3 had no inhibition effect against PTP1B, an important target enzyme for the treatment of diabetes, while the dehydro derivative of 1 [dehydroeuryspongin A (4)] exhibited inhibitory activity (IC(50)=3.6 μM).

Strongylophorines, new protein tyrosine phosphatase 1B inhibitors, from the marine sponge Strongylophora strongilata collected at Iriomote Island.

A new meroditerpene, 26-O-ethylstrongylophorine-14 (1), was isolated from the Okinawan marine sponge Strongylophora strongilata together with six known strongylophorines: 26-O-methylstrongylophorine-16 (2) and strongylophorines-2 (3), -3 (4), -8 (5), -15 (6), and -17 (7). The structure of 1 was assigned on the basis of its spectroscopic data. Compound 1 inhibited the activity of protein tyrosine phosphatase 1B (PTP1B) with an IC50 value of 8.7 μM, while known compounds 2-8 gave IC50 values of 8.5, >24.4, 9.0, 21.2, 11.9, and 14.8 μM, respectively. Oleanolic acid, a positive control, inhibited PTP1B activity at 0.7 μM (IC50). The inhibitory activities of strongylophorines possessing the acetal moiety at C-26 (1, 2, and 6) were stronger than those of the lactone derivatives (3 and 5). This is the first study to demonstrate that meroditerpenes inhibit PTP1B activity.

Absolute structures and bioactivities of euryspongins and eurydiene obtained from the marine sponge Euryspongia sp. collected at Iriomote Island.

Three unique sesquiterpenes, named euryspongins A-C (1-3), have been isolated from the marine sponge Euryspongia sp. The absolute configuration of 1 was assigned as (4R,6R,9S) by comparing its experimental Electronic Circular Dichroism (ECD) spectrum with the calculated ECD spectra of both enantiomers, and the absolute configurations of 2, 3 and artifact 4 were suggested on the basis of that of 1 by assuming common biogenesis of 1-3. These absolute configurations were opposite to those depicted in the previous communication. Further separation of the remaining fractions lead to the isolation of a new C11-polyketide, named as eurydiene (5), together with a known C11-polyketide, nakitriol (6). The structure of 5 was assigned on the basis of its spectroscopic data as a bicyclic alcohol with a diene side chain. Dehydroeuryspongin A (4) inhibited protein tyrosine phosphatase 1B (PTP1B), an important target enzyme for the treatment of type II diabetes and obesity, with an IC50 value of 3.58μM. Moreover, compound 4 did not inhibit the proliferation of human hepatoma Huh-7 cells at 100μM. One of the locations in which PTP1B has been detected is hepatocytes. Compounds 1-3, 5, and 6 were not active against PTP1B. The growth of human colon (HCT-15) and T-cell lymphoma (Jurkat) cells was not disturbed by compounds 1-6.

Anti-Mycobacterial Nucleoside Antibiotics from a Marine-Derived Streptomyces sp. TPU1236A

Five new nucleoside antibiotics, named streptcytosines A–E (1–5), and six known compounds, de-amosaminyl-cytosamine (6), plicacetin (7), bamicetin (8), amicetin (9), collismycin B (10), and SF2738 C (11), were isolated from a culture broth of Streptomyces sp. TPU1236A collected in Okinawa, Japan. The structures of new compounds were elucidated on the basis of their spectroscopic data (HRFABMS, IR, UV, and 2D NMR experiments including 1H-1H COSY, HMQC, HMBC, and NOESY spectra). Streptcytosine A (1) belonged to the amicetin group antibiotics, and streptcytosines B–E (2–5) were derivatives of de-amosaminyl-cytosamine (6), 2,3,6-trideoxyglucopyranosyl cytosine. Compound 1 inhibited the growth of Mycobacterium smegmatis (MIC = 32 µg/mL), while compounds 2–5 were not active at 50 µg/disc. Bamicetin (8) and amicetin (9) showed the MICs of 16 and 8 µg/mL, respectively.

Papuamine causes autophagy following the reduction of cell survival through mitochondrial damage and JNK activation in MCF-7 human breast cancer cells

We previously reported that extracts of an Indonesian marine sponge Haliclona sp. showed potent cytotoxicity and the induction of apoptosis against human solid cancer cell lines. In this study, we examine the cytotoxic mechanism of the major chemical compound, papuamine, on MCF-7 human breast cancer cells. Papuamine at 5 μM did not show significant cytotoxic effects after incubation for 24 h, but autophagosome vesicular formation was apparent. At 10 μM of papuamine, significant reduction in cell survival was observed at 12 h, and increases in autophagy at this concentration were time-dependent and apparent before the appearance of cytotoxic effects. Both the release of cytochrome c to the cytosol and increase in Bax in the mitochondrial fraction were found to be concentration-dependent. Moreover, mitochondrial membrane potential shows concentration- and time-dependent decreases with exposure to papuamine. The release of cytochrome c has been shown to be accompanied by an increase in JNK activation. 3-Methyladenine (MA), a classical autophagy inhibitor showed increased JNK activation by exposure to papuamine. In conclusion, our results indicate that papuamine causes earlier onset autophagy and delayed reduction of cell survival through mitochondrial damage and JNK activation in MCF-7 cells.