Garcinia mangostana L. Pericarp Extract and Its Active Compound α-Mangostin as Potential Inhibitors of Immune Checkpoint Programmed Death Ligand-1.

α-Mangostin, a major xanthone found in mangosteen (Garcinia mangostana L., Family Clusiaceae) pericarp, has been shown to exhibit anticancer effects through multiple mechanisms of action. However, its effects on immune checkpoint programmed death ligand-1 (PD-L1) have not been studied. This study investigated the effects of mangosteen pericarp extract and its active compound α-mangostin on PD-L1 by in vitro and in silico analyses. HPLC analysis showed that α-mangostin contained about 30% w/w of crude ethanol extract of mangosteen pericarp. In vitro experiments in MDA-MB-231 triple-negative breast cancer cells showed that α-mangostin and the ethanol extract significantly inhibit PD-L1 expression when treated for 72 h with 10 µM or 10 µg/mL, respectively, and partially inhibit glycosylation of PD-L1 when compared to untreated controls. In silico analysis revealed that α-mangostin effectively binds inside PD-L1 dimer pockets and that the complex was stable throughout the 100 ns simulation, suggesting that α-mangostin stabilized the dimer form that could potentially lead to degradation of PD-L1. The ADMET prediction showed that α-mangostin is lipophilic and has high plasma protein binding, suggesting its greater distribution to tissues and its ability to penetrate adipose tissue such as breast cancer. These findings suggest that α-mangostin-rich mangosteen pericarp extract could potentially be applied as a functional ingredient for cancer chemoprevention.

New insights into the neuroprotective and beta-secretase1 inhibitor profiles of tirandamycin B isolated from a newly found Streptomyces composti sp. nov.

Tirandamycin (TAM B) is a tetramic acid antibiotic discovered to be active on a screen designed to find compounds with neuroprotective activity. The producing strain, SBST2-5T, is an actinobacterium that was isolated from wastewater treatment bio-sludge compost collected from Suphanburi province, Thailand. Taxonomic characterization based on a polyphasic approach indicates that strain SBST2-5T is a member of the genus Streptomyces and shows low average nucleotide identity (ANI) (81.7%), average amino-acid identity (AAI) (78.5%), and digital DNA-DNA hybridization (dDDH) (25.9%) values to its closest relative, Streptomyces thermoviolaceus NBRC 13905T, values that are significantly below the suggested cut-off values for the species delineation, indicating that strain SBST2-5T could be considered to represent a novel species of the genus Streptomyces. The analysis of secondary metabolites biosynthetic gene clusters (smBGCs) in its genome and chemical investigation led to the isolation of TAM B. Interestingly, TAM B at 20 µg/mL displayed a suppressive effect on beta-secretase 1 (BACE1) with 68.69 ± 8.84% inhibition. Molecular docking simulation reveals the interaction mechanism between TAM B and BACE1 that TAM B was buried in the pocket of BACE-1 by interacting with amino acids Thr231, Asp 228, Gln73, Lys 107 via hydrogen bond and Leu30, Tyr71, Phe108, Ile118 via hydrophobic interaction, indicating that TAM B represents a potential active BACE1 inhibitor. Moreover, TAM B can protect the neuron cells significantly (% neuron viability = 83.10 ± 9.83% and 112.72 ± 6.83%) from oxidative stress induced by serum deprivation and Aß1-42 administration models at 1 ng/mL, respectively, without neurotoxicity on murine P19-derived neuron cells nor cytotoxicity against Vero cells. This study was reportedly the first study to show the neuroprotective and BACE1 inhibitory activities of TAM B.

Selective α3ß4 Nicotinic Acetylcholine Receptor Ligand as a Potential Tracer for Drug Addiction.

α3ß4 Nicotinic acetylcholine receptor (nAChR) has been recognized as an emerging biomarker for the early detection of drug addiction. Herein, α3ß4 nAChR ligands were designed and synthesized to improve the binding affinity and selectivity of two lead compounds, (S)-QND8 and (S)-T2, for the development of an α3ß4 nAChR tracer. The structural modification was achieved by retaining the key features and expanding the molecular structure with a benzyloxy group to increase the lipophilicity for blood-brain barrier penetration and to extend the ligand-receptor interaction. The preserved key features are a fluorine atom for radiotracer development and a p-hydroxyl motif for ligand-receptor binding affinity. Four (R)- and (S)-quinuclidine-triazole (AK1-AK4) were synthesized and the binding affinity, together with selectivity to α3ß4 nAChR subtype, were determined by competitive radioligand binding assay using [3H]epibatidine as a radioligand. Among all modified compounds, AK3 showed the highest binding affinity and selectivity to α3ß4 nAChR with a Ki value of 3.18 nM, comparable to (S)-QND8 and (S)-T2 and 3069-fold higher affinity to α3ß4 nAChR in comparison to α7 nAChR. The α3ß4 nAChR selectivity of AK3 was considerably higher than those of (S)-QND8 (11.8-fold) and (S)-T2 (294-fold). AK3 was shown to be a promising α3ß4 nAChR tracer for further development as a radiotracer for drug addiction.

Dietary anthocyanins inhibit insulin fibril formation and cytotoxicity in 3T3-L1 preadipocytes.

Insulin fibril formation decreases the effectiveness of insulin therapy and causes amyloidosis in diabetes. Studies suggest that phytochemicals are capable of inhibiting fibril formation. Herein, we investigated the inhibitory effects of anthocyanins, including cyanidin, cyanidin-3-glucoside (C3G), cyanidin-3-rutinoside (C3R), malvidin, and malvidin-3-glucoside (M3G) on fibril formation. Our results revealed that anthocyanins (50-200 µM) significantly reduced the formation of insulin fibrils by increasing lag times and decreasing ThT fluorescence at the plateau phase. These findings were confirmed by TEM images, which showed reduced fibril length and number. Furthermore, FTIR analysis indicated that anthocyanins reduced the secondary structure transition of insulin from α-helix to ß-sheet. Anthocyanins interacted with monomeric insulin (residues B8-B30) via H-bonds, van der Waals, and hydrophobic interactions, covering the fibril-prone segments of insulin (residues B12-B17). Based on the structure-activity analysis, the presence of glycosides and hydroxyl groups on phenyl rings increased intermolecular interaction, mediating the inhibitory effect of anthocyanins on fibril formation in the order of malvidin < cyanidin < M3G < C3G < C3R. Moreover, anthocyanins formed H-bonds with preformed insulin fibrils, except for malvidin. In preadipocytes, C3R, C3G, and cyanidin attenuated insulin fibril-induced cytotoxicity. In conclusion, anthocyanins are effective inhibitors of insulin fibril formation and cytotoxicity.

Isolation of manumycin-type derivatives and genome characterization of a marine Streptomyces sp. C1-2.

A marine actinomycete strain C1-2 was taxonomically characterized as the genus Streptomyces, based on whole-genome sequence analysis. The highest average nucleotide identity (ANI) value (98.96%) and digital DNA-DNA hybridization (DDH) value (90.4%) were observed between Streptomyces sp. C1-2 and Streptomyces griseoaurantiacus. Thus, Streptomyces sp. C1-2 could be identified as S. griseoaurantiacus. Genome analysis revealed that Streptomyces sp. C1-2 contained 22 biosynthetic gene clusters (BGCs) for secondary metabolites, where among them, 54% have low similarities with known BGCs. The chemical investigation led to the isolation of three new manumycin-type derivatives and two known analog antibiotics named SW-B and cornifronin B. All compounds showed antioxidant activity with the half-maximal inhibitory concentration (IC50) values in a range of 50.82 ± 0.8-112.04 ± 1.0 µg/mL with no cytotoxicity against Vero cells. This is the first report of the antioxidant property of manumycin-type derivatives. Moreover, two known compounds exhibited antifungal activity against Phytophthora capsici, Fusarium oxysporum f. sp. cucumerinum, and Magnaporthe grisea, with the minimum inhibitory concentration (MIC) values in a range of 125-500 µg/mL.

In Silico Finding of Key Interaction Mediated α3ß4 and α7 Nicotinic Acetylcholine Receptor Ligand Selectivity of Quinuclidine-Triazole Chemotype.

The selective binding of six (S)-quinuclidine-triazoles and their (R)-enantiomers to nicotinic acetylcholine receptor (nAChR) subtypes α3ß4 and α7, respectively, were analyzed by in silico docking to provide the insight into the molecular basis for the observed stereospecific subtype discrimination. Homology modeling followed by molecular docking and molecular dynamics (MD) simulations revealed that unique amino acid residues in the complementary subunits of the nAChR subtypes are involved in subtype-specific selectivity profiles. In the complementary ß4-subunit of the α3ß4 nAChR binding pocket, non-conserved AspB173 through a salt bridge was found to be the key determinant for the α3ß4 selectivity of the quinuclidine-triazole chemotype, explaining the 47-327-fold affinity of the (S)-enantiomers as compared to their (R)-enantiomer counterparts. Regarding the α7 nAChR subtype, the amino acids promoting a however significantly lower preference for the (R)-enantiomers were the conserved TyrA93, TrpA149 and TrpB55 residues. The non-conserved amino acid residue in the complementary subunit of nAChR subtypes appeared to play a significant role for the nAChR subtype-selective binding, particularly at the heteropentameric subtype, whereas the conserved amino acid residues in both principal and complementary subunits are essential for ligand potency and efficacy.

A novel diterpene agent isolated from Microbispora hainanensis strain CSR-4 and its in vitro and in silico inhibition effects on acetylcholine esterase enzyme.

An actinomycete strain CSR-4 was isolated from the rhizosphere soil of Zingiber montanum. Taxonomic characterization revealed strain CSR-4 was a member of the genus Microbispora. Whole-genome sequence analysis exhibited the highest average nucleotide identity (ANI) value (95.34%) and digital DNA-DNA hybridization (DDH) value (74.7%) between strain CSR-4 and the closest relative M. hainanensis DSM 45428T, which was in line with the assignment to same species. In addition, a new diterpene compound, 2α-hydroxy-8(14), 15-pimaradien-17, 18-dioic acid, and nine known compounds were isolated from the ethyl acetate crude extract of fermentation broth. Interestingly, a new diterpene displayed the suppressive effect on the recombinant human acetylcholinesterase (rhAChE) enzymes (IC50 96.87 ± 2.31 µg/ml). In silico studies based on molecular docking and molecular dynamics (MD) simulations were performed to predict a binding mode of the new compound into the binding pocket of the rhAChE enzyme and revealed that some amino acids in the peripheral anions site (PAS), anionic subsite, oxyanion site and catalytic active site (CAS) of the rhAChE have interacted with the compound. Therefore, our new compound could be proposed as a potential active human AChE inhibitor. Moreover, the new compound can protect significantly the neuron cells (% neuron viability = 88.56 ± 5.19%) from oxidative stress induced by serum deprivation method at 1 ng/ml without both neurotoxicities on murine P19-derived neuron cells and cytotoxicity against Vero cells.