In silico discovery of acylated flavonol monorhamnosides from Eriobotrya japonica as natural, small-molecular weight inhibitors of XIAP BIR3.

Targeting the baculoviral inhibitor of apoptosis proteins repeat (BIR) 3 of X-linked inhibitor of apoptosis proteins (XIAP) represents an innovative strategy for the design of chemosensitizers. Acylated flavonol monorhamnosides (AFMR) from Eriobotrya japonica Lindl. (Rosaceae) were virtually predicted as ligands of the XIAP BIR3 domain by using a previously generated pharmacophore model. From the methanol leaf extract of E. japonica an enriched mixture of AFMR was obtained showing chemosensitizing potential in combination with etoposide in XIAP-overexpressing Jurkat cells. The HPLC-SPE-NMR hyphenated technique facilitated the structure elucidation of three known and two new natural AFMR. The main constituent and virtual hit, kaempferol-3-O-α-l-(2″,4″-di-E-p-coumaroyl)-rhamnoside (3) was isolated from the enriched fraction. Applying a fluorescence polarization based binding assay, 3 was identified as XIAP BIR3 ligand with a dose-dependent affinity (IC50 10.4 µM). Further, 3 induced apoptosis in XIAP-overexpressing Jurkat cells and activated caspase-9 in combination with etoposide. Docking experiments revealed a major impact of the coumaric acid and sugar moieties of 3 on XIAP BIR3 binding, which was experimentally confirmed. To conclude, this study elucidates 3 as natural, small-molecular weight XIAP BIR3 inhibitor using a combination of in silico and HPLC-SPE-NMR hyphenated techniques.

11beta-Hydroxysteroid dehydrogenase 1 inhibiting constituents from Eriobotrya japonica revealed by bioactivity-guided isolation and computational approaches.

The inhibition of 11beta-hydroxysteroid dehydrogenase 1 (11beta-HSD1), which catalyzes the conversion of inactive 11-ketoglucocorticoids to active 11beta-hydroxyglucocorticoids, emerged as promising strategy to treat symptoms of the metabolic syndrome, including obesity and type 2 diabetes. In this study the leaves of the anti-diabetic medicinal plant loquat (Eriobotrya japonica) were phytochemically investigated following hints from a pharmacophore-based virtual screening and a bioactivity-guided approach. Determination of the 11beta-HSD1 and 11beta-HSD2 inhibitory activities in cell lysates revealed triterpenes from the ursane type as selective, low micro-molar inhibitors of 11beta-HSD1, that is, corosolic acid (1), 3-epicorosolic acid methyl ester (4), 2-alpha hydroxy-3-oxo urs-12-en-28-oic acid (6), tormentic acid methyl ester (8), and ursolic acid (9). Importantly, a mixture of loquat constituents with moderate activities displayed a pronounced additive effect. By means of molecular modeling studies and the identification of the 11beta-HSD1-inhibiting 11-keto-ursolic acid (17) and 3-acetyl-11-keto-ursolic acid (18) a structure-activity relationship was deduced for this group of pentacyclic triterpenes. The mechanism of action elucidated in the present work together with the previously determined pharmacological activities provides these natural products with an astonishing multi-targeted anti-diabetic profile.

Neoandrographolide from Andrographis paniculata as a potential natural chemosensitizer.

Extracts of the traditional medicinal herb Andrographis paniculata and its main constituents are described in the literature as showing anticancer activity. The aim of this study was to isolate the main constituents of a commercially available phytotherapeutic preparation of A. paniculata and to determine their chemosensitizing potential in a leukemia cell line. Chromatographic separation steps resulted in the isolation of the diterpenes andrographolide (1) and 14-deoxy-11,12-didehydroandrographolide (3) and the diterpene glucoside neoandrographolide (2). The combination of these constituents with suboptimal concentrations of etoposide revealed compound 2 as chemosensitizer in S-Jurkat and X chromosome-linked inhibitor of apoptosis protein (XIAP)-overexpressing Jurkat cells, a model for chemoresistance.