Discovery of Celludinone C and Its SOAT Inhibitory Activity

Academic Background

Sterol O-Acyltransferase (SOAT) is an enzyme that catalyzes the esterification of cholesterol and plays a critical role in maintaining intracellular lipid homeostasis. SOAT has two isozymes, SOAT1 and SOAT2, which exhibit significant differences in tissue distribution and structure. SOAT1 is widely expressed in various tissues and cells, while SOAT2 is primarily found in the liver and intestines. Research has shown that SOAT1 is closely associated with diseases such as Alzheimer’s and cancer, while SOAT2 is a potential therapeutic target for cardiovascular diseases. Therefore, developing compounds that selectively inhibit SOAT1 or SOAT2 holds significant clinical importance.

Previously, researchers isolated two new SOAT inhibitors, Celludinone A and B, from the fungus Talaromyces cellulolyticus BF-0307. Celludinone A inhibits both SOAT1 and SOAT2, while Celludinone B selectively inhibits SOAT2. To further explore the biological and chemical properties of Celludinone-like compounds, researchers continued to search for analogs in the fungal culture broth and successfully discovered a new dihydroisobenzofuran compound—Celludinone C.

Source of the Paper

This paper was co-authored by researchers from the Graduate School of Pharmaceutical Sciences at Kitasato University, Japan, including Reiko Seki, Kenichiro Nagai, Keisuke Kobayashi, and others. It was published online on November 14, 2024, in The Journal of Antibiotics. The study was supported by the Kitasato University Research Grant and the Promotion and Mutual Aid Corporation for Private Schools of Japan.

Research Process

1. Fungal Cultivation and Compound Extraction

Researchers first inoculated the Talaromyces cellulolyticus BF-0307 strain into a 500 mL flask containing seed medium and cultured it at 27°C with shaking for 3 days. Subsequently, the seed culture was transferred to a 10 L fermenter, and fermentation was carried out for 6 days using production medium under the same conditions. After fermentation, compounds were extracted from the culture broth using acetone, and target compounds with specific physicochemical characteristics were screened through liquid chromatography (LC) and mass spectrometry (MS) analysis.

2. Compound Isolation and Purification

Using LC/UV and LC/MS analysis, researchers isolated four structurally related compounds from the culture broth, including the newly discovered Celludinone C (1) and the known compounds Paeciloxanthone (2), Talaroxanthenone (3), and Arugosin I (4). These compounds were further purified using medium-pressure preparative column chromatography and high-performance liquid chromatography (HPLC) to obtain pure samples.

3. Structural Elucidation

Researchers used one-dimensional/two-dimensional nuclear magnetic resonance (NMR) and electronic circular dichroism (ECD) spectroscopy to elucidate the structure of Celludinone C. The results showed that the molecular formula of Celludinone C is C20H22O4, with one chiral center (C-8). Through semi-synthetic experiments, researchers further validated its structure and determined its absolute configuration as 8R.

4. Evaluation of SOAT Inhibitory Activity

Using Chinese hamster ovary (CHO) cells expressing human SOAT1 and SOAT2, researchers evaluated the inhibitory activity of compounds 1–4 against SOAT1 and SOAT2. The results showed that Celludinone C (1) exhibited strong inhibitory activity against both SOAT1 and SOAT2, with IC50 values of 8.5 µM and 12 µM, respectively, indicating dual inhibition. Additionally, researchers found significant differences in the inhibitory activity between the stereoisomers (+)-1 and (-)-1, with (+)-1 showing higher activity than (-)-1.

Key Findings

1. Discovery and Structural Elucidation of Celludinone C: Researchers successfully isolated a new dihydroisobenzofuran compound, Celludinone C, from the culture broth of Talaromyces cellulolyticus BF-0307 and determined its structure and absolute configuration using NMR and ECD techniques.

2. SOAT Inhibitory Activity: Celludinone C exhibited strong inhibitory activity against both SOAT1 and SOAT2, with IC50 values of 8.5 µM and 12 µM, respectively. Additionally, significant differences in inhibitory activity were observed between its stereoisomers (+)-1 and (-)-1.

3. Speculation on Biosynthetic Pathways: Researchers hypothesized that Arugosin I (4) might be a common precursor for Celludinone B, Celludinone C, and xanthone-like compounds, with Celludinone C being generated through enzyme-catalyzed stereoselective reduction and dehydration reactions.

Conclusions and Significance

This study successfully discovered a new SOAT inhibitor, Celludinone C, and revealed its structure and biological activity. The dual inhibitory activity of Celludinone C against SOAT1 and SOAT2 provides a scientific basis for its potential applications in treating Alzheimer’s disease, cancer, and cardiovascular diseases. Additionally, researchers speculated on the biosynthetic pathways of Celludinone-like compounds, offering theoretical support for future optimization of their production through synthetic biology approaches.

Research Highlights

1. Discovery of a New Compound: Celludinone C is a novel dihydroisobenzofuran compound with a unique structure and biological activity.

2. Dual SOAT Inhibitory Activity: Celludinone C exhibits strong inhibitory activity against both SOAT1 and SOAT2, highlighting its potential for treating various diseases.

3. Activity Differences Between Stereoisomers: Researchers found significant differences in inhibitory activity between the stereoisomers (+)-1 and (-)-1 of Celludinone C, providing important clues for developing highly selective SOAT inhibitors.

Additional Valuable Information

Researchers also validated the structure of Celludinone C through semi-synthetic experiments and discovered that it undergoes racemization under acidic conditions. This finding provides important insights into the stability of such compounds and their metabolism in biological systems.

This study not only discovered a new SOAT inhibitor but also provided a scientific basis for its potential therapeutic applications, holding significant theoretical and practical importance.