Structural Insight into the Interactions between Structurally Similar Inhibitors and SIRT6.

Sirtuin 6 (SIRT6) is an NAD+-dependent deacetylase with a significant role in 20% of all cancers, such as colon cancers and rectal adenocarcinoma. However, there is currently no effective drug for cancers related to SIRT6. To explore potential inhibitors of SIRT6, it is essential to reveal details of the interaction mechanisms between inhibitors and SIRT6 at the atomic level. The nature of small molecules from herbs have many advantages as inhibitors. Based on the conformational characteristics of the inhibitor Compound 9 (Asinex ID: BAS13555470), we explored the natural molecule Scutellarin, one compound of Huang Qin, which is an effective herb for curing cancer that has been described in the Traditional Chinese Medicine (TCMS) library. We investigated the interactions between SIRT6 and the inhibitors using molecular dynamics (MD) simulations. We illustrated that the structurally similar inhibitors have a similar binding mode to SIRT6 with residues-Leu9, Phe64, Val115, His133 and Trp188. Hydrophobic and π-stacking interactions play important roles in the interactions between SIRT6 and inhibitors. In summary, our results reveal the interactive mechanism of SIRT6 and the inhibitors and we also provide Scutellarin as a new potential inhibitor of SIRT6. Our study provides a new potential way to explore potential inhibitors from TCMS.

Indole alkaloids from the aerial parts of Kopsia fruticosa and their cytotoxic, antimicrobial and antifungal activities.

A chemical investigation on the 80% EtOH extract of the aerial parts of Kopsia fruticosa led to five new indole alkaloids, kopsifolines G-K (1-5), and one known alkaloid, kopsifoline A (6). Structural elucidation of all the compounds were performed by spectral methods such as 1D and 2D (1H-1H COSY, HMQC, and HMBC) NMR spectroscopy, in addition to high resolution mass spectrometry. The isolated components were evaluated in vitro for cytotoxic activities against seven tumor cell lines, antimicrobial activities against two Gram-positive bacteria and five Gram-negative bacteria, and antifungal activities against five pathogens. As a result, alkaloids 3-5 exhibited some cytotoxicity against all of seven tested tumor cell lines (HS-1, HS-4, SCL-1, A431, BGC-823, MCF-7, and W480) with IC50 values of 11.8-13.8, 10.3-12.5, and 7.3-9.5 µM, respectively. Alkaloids 3-5 also possessed significant antimicrobial and antifungal activities which was reported for the first time for the alkaloids isolated from Kopsia genus.

A novel matrine derivative WM622 inhibits hepatocellular carcinoma by inhibiting PI3K/AKT signaling pathways.

Hepatocellular carcinoma (HCC) is among the most common lethal cancers of the digestive system with poor prognosis rates and ineffective therapeutic options. Matrine, a traditional Chinese medicine found in the roots of sophora species, has been used in the clinical treatment of liver fibrosis, chronic hepatitis B and other diseases. We have synthesized a matrine derivatives named WM622 (C26H35ON3S2) with a significant inhibitory effect on transplanted tumors in vivo. The half inhibitory concentration (IC50) of WM622 is 34 µM, which is much lower than matrine. WM622 inhibited the proliferation and promoted apoptosis of hepatocellular carcinoma cells significantly, and the cell cycle was blocked in G0/G1 phase. The protein phosphorylation levels of EGFR, AKT, PI3K and GSK3ß (p-EGFR, p-AKT, p-PI3K, and p-GSK3ß) were also decreased by WM622 treatment dose dependently. In tumor-bearing mice, WM622 could reduce the tumor volumes. In conclusion, the study demonstrated that WM622 could inhibit the proliferation of the hepatocellular carcinoma both in vivo and in vitro by inducing apoptosis, blocking cell cycle in G0/G1 phase and inhibiting the PI3K/AKT signal pathways.

Alkaloids from Lycoris caldwellii and their particular cytotoxicities against the astrocytoma and glioma cell lines.

Phytochemical investigation of the ethanol extract of the bulbs of Lycoris caldwellii afforded four new alkaloids, (+)-N-methoxylcarbonyl-nandigerine (1), (+)-N-methoxycarbonyl-lindcarpine (2), (+)-10-O-methylhernovine N-oxide (3), and (+)-3-hydroxy-anhydrolycorine N-oxide (4). Structural elucidation of all the compounds were performed by spectral methods such as 1D and 2D (¹H-¹H COSY, HMQC, and HMBC) NMR spectroscopy, in addition to high resolution mass spectrometry. All the alkaloids were in vitro evaluated for their cytotoxic activities against eight tumor cell lines (BEN-MEN-1, CCF-STTG1, CHG-5, SHG-44, U251, BGC-823, HepG2, and SK-OV-3). Alkaloids 1 and 2 exhibited particular cytotoxic activities against astrocytoma and glioma cell lines with IC50 of 9.2-11.3 µM and 10.4-12.2 µM respectively.

Cytotoxic and antimalarial amaryllidaceae alkaloids from the bulbs of Lycoris radiata.

Phytochemical investigation of the 80% ethanol extract of the bulbs of Lycoris radiata resulted in the isolation of five new Amaryllidaceae alkaloids: (+)-5,6-dehydrolycorine (1), (+)-3α,6ß-diacetyl-bulbispermine (2), (+)-3α-hydroxy-6ß-acetyl- bulbispermine (3), (+)-8,9-methylenedioxylhomolycorine-N-oxide (5), and 5,6-dihydro-5- methyl-2-hydroxyphenanthridine (7), together with two known compounds, (+)-3α-methoxy- 6ß-acetylbulbispermine (4) and (+)-homolycorine- N-oxide (6). Structural elucidation of all the compounds were performed by spectral methods such as 1D and 2D (1H-1H COSY, HMQC, and HMBC) NMR spectroscopy, in addition to high resolution mass spectrometry. Alkaloid 1 showed potent cytotoxicity against astrocytoma and glioma cell lines (CCF-STTG1, CHG-5, SHG-44, and U251), as well as HL-60, SMMC-7721, and W480 cell lines with IC(50) values of 9.4-11.6 µM. Additonally, compound 1 exhibited antimalarial activity with IC(50) values of 2.3 µM for D-6 strain and 1.9 µM for W-2 strain of Plasmodium falciparum.

Two new triterpenoid acids from Kadsura coccinea.

An investigation of EtOAc extracts of Kadsura coccinea (Lem.) A. C. Smith, has led to the isolation of two new compounds characterized as 3-hydroxy-12-hydroxyl coccinic acid (1) and 3-hydroxy-neokadsuranic acid A (2). Their structures were established by 1D and 2D NMR techniques and mass spectroscopy. Antiproliferative effects of the isolated compounds were evaluated against four human tumor cell lines (A549, HCT116, HL-60 and HepG2), and it was found that compound 1 exhibited antiproliferative effects with IC(50) values ranging from 3.01 to 18.08 µg/mL.