Clonoamide, a new inhibitor of sterol O-acyltransferase, produced by Clonostachys sp. BF-0131

Targeting Sterol O-Acyltransferase/Acyl-CoA:Cholesterol Acyltransferase (ACAT): A Perspective on Small-Molecule Inhibitors and Their Therapeutic Potential

Sterol O-acyltransferase (SOAT) is a membrane-bound enzyme that aids the esterification of cholesterol and fatty acids to cholesterol esters. SOAT has been studied extensively as a potential drug target, since its inhibition can serve as an alternative to statin therapy. Two SOAT isozymes that have discrete functions in the human body, namely, SOAT1 and SOAT2, have been characterized. Over three decades of research has focused on candidate SOAT1 inhibitors with unsatisfactory results in clinical trials. Recent research has focused on targeting SOAT2 selectively. In this perspective, we summarize the literature covering various SOAT inhibitory agents and discuss the design, structural requirements, and mode of action of SOAT inhibitors.

A Mixture of Atropisomers Enhances Neutral Lipid Degradation in Mammalian Cells with Autophagy Induction

Atropisomers with a biaryl dihydronaphthopyranone structure, dinapinones A1 (DPA1) (M position) and A2 (DPA2) (P position), were isolated from the fungus culture broth of Talaromyces pinophilus FKI-3864 as inhibitors of [14C]neutral lipid ([14C]triacylglycerol (TG) and [14C]cholesteryl ester (CE)) synthesis from [14C]oleic acid in Chinese hamster ovary-K1 (CHO-K1) cells. DPA2 inhibited [14C]TG and [14C]CE synthesis (IC50s, 0.65 and 5.6 μM, respectively), but DPA1 had no inhibitory activity on [14C]TG and [14C]CE synthesis even at 12 μM. However, a 1:1 mixture of DPA1 and DPA2 (DPAmix) had the most potent inhibitory activity on [14C]TG and [14C]CE synthesis (IC50s, 0.054 and 0.18 μM, respectively). The mechanism of action of DPAmix was investigated. DPAmix had no effects on the enzymes involved in neutral lipid synthesis, while DPAmix enhanced the degradation of [14C]neutral lipids with concomitant decrease in cytosolic lipid droplets accumulated in CHO-K1 cells. From analysis of autophagy marker proteins, DPAmix caused dose-dependent induction of microtubule-associated protein light chain 3-II (LC3-II) and degradation of p62. In the autophagic flux assay using bafilomycin A1, DPAmix upregulated autophagosome turnover. These results reveal that DPAmix enhances neutral lipid degradation together with induction of autophagy.

Anti-Rhizopus activity of tanzawaic acids produced by the hot spring-derived fungus Penicillium sp. BF-0005

A silkworm infection assay with the pathogenic fungus Rhizopus oryzae was established. Microbial culture broths were screened for anti-Rhizopus antibiotics using this assay. A new compound, tanzawaic acid R was isolated along with known and structurally related tanzawaic acids and arohynapene A from the culture broth of the hot spring-derived fungus Penicillium sp. BF-0005. The structure of tanzawaic acid R was elucidated by various spectroscopic data including 1D and 2D nuclear magnetic resonance spectroscopy. Tanzawaic acids A, B, C, and R and arohynapene A exhibited antifungal activity against R. oryzae. Tanzawaic acids A and B dose-dependently exerted therapeutic effects in the silkworm infection assay with R. oryzae.

A new polyketide glycoside from the rhizospheric Clonostachys rogersoniana associated with Panax notoginseng

A new polyketide glycoside rogerson A (1), along with two known compounds, rogerson B (2) and (22E)-5α,8α-epidioxyergosta-6,22-dien-3β-ol (3), was obtained from the solid fermentation of Clonostachys rogersoniana, which was isolated from the rhizosphere soil of Panax notoginseng. Rogerson B (2) was isolated for the first time from a natural source. Their structure was determined by extensive analyses of NMR and MS studies. Compounds 1 and 2 were tested for its cytotoxicity against five human cancer cell lines.

Simplifungin and Valsafungins, Antifungal Antibiotics of Fungal Origin

The targets of antifungal antibiotics in clinical use are more limited than those of antibacterial antibiotics. Therefore, new antifungal antibiotics with different mechanisms of action are desired. In the course of our screening for antifungal antibiotics of microbial origins, new antifungal antibiotics, simplifungin (1) and valsafungins A (2) and B (3), were isolated from cultures of the fungal strains Simplicillium minatense FKI-4981 and Valsaceae sp. FKH-53, respectively. The structures of 1 to 3 including their absolute stereochemistries were elucidated using various spectral analyses including NMR and collision-induced dissociation (CID)-MS/MS as well as chemical approaches including modifications to the Mosher's method. They were structurally related to myriocin. They inhibited the growth of yeast-like and zygomycetous fungi with MICs ranging between 0.125 and 8.0 μg/mL. An examination of their mechanisms of action by the newly established assay using LC-MS revealed that 1 and 2 inhibited serine palmitoyltransferase activity, which is involved in sphingolipid biosynthesis, with IC50 values of 224 and 24 nM, respectively.