Synthesis and evaluation of several oleanolic acid glycoconjugates as protein tyrosine phosphatase 1B inhibitors

Functional analysis of tandem glycosyltransferases catalyzing the O-glycosylation of flavonoid 4'-O-glycosyl-6-C-glycosides biosynthesis from Isatis indigotica

Flavonoid O-glycosyl-C-glycosides with promising biological activities including antitumor, antidiabetes, and antibacterials are the primary active ingredients of the medicinal plant Isatis indigotica's leaves. However, O-glycosyltransferases catalyzing flavonoid O-glycosyl-C-glycosides biosynthesis in I. indigotica's leaves remain unclear. In this study, guided by genome-wide investigation and phylogenetic analyses, 89 glycosyltransferases were obtained and clustered into 18 families. In vitro enzyme assays demonstrated that eight novel glycosyltransferases could catalyze the 4'-O-glycosylation of flavonoid 6-C-glycosides, and exhibited different catalytic properties. Moreover, tandem UGT73Bs, IiUGT15 and IiUGT16, could catalyze not only 4'-O-glycosylate flavonoid 6-C-glycosides such as isovitexin, isoorientin, and isoscoparin but also 7-O-glycosylate flavonoids, and hydrolyze the glucose moiety of flavonoid O-glycosides. Homology modeling and site-directed mutagenesis uncovered that the amino acids interacting with acceptors were highly conserved between IiUGT15 and IiUGT16, with various degreed effects on 4'-O-glycosylation, potentially leading to differences in their catalytic activity. Isoorientin-4'-O-β-D-glucoside was synthesized in Escherichia coli without the exogenous supplementation of UDP-glucose. Overall, this study offered new biocatalysts to attain 4'-O-glycosylation of flavonoid C-glycosides for drug discovery and established a foundation for the biomanufacturing of critical flavonoid O-glycosyl-C-glycosides.

Discovery of novel oleanolic acid glycoside derivatives targeting PTP1B/PI3K/AKT signaling pathway for the treatment of breast cancer

Protein tyrosine phosphatase 1B (PTP1B) has been identified as a key drug target for anti-tumor drug development. Oleanolic acid (OA) has been proved to be an inhibitor of PTP1B, but its poor water solubility, low bioavailability and poor activity in vivo limit its clinical efficacy. In this study, a total of 47 new OA derivatives including heteroatom derivatives, ester derivatives, amino substitution derivatives and Schiff base derivatives were designed and synthesized. Among them, OA-Br-1 had stronger inhibition and selectivity on PTP1B than OA, with IC50 value of 7.08 ± 5.05 μM for PTP1B and 222.28 ± 0.11 μM for TCPTP. In addition, OA-Br-1 significantly inhibited the proliferation and induced apoptosis of breast cancer cells, and in vivo nude mice experiments also showed that OA-Br-1 could inhibit the growth of breast tumors. Then network pharmacology was used to predict the targets of OA-Br-1, and the PPI network map between compound - breast cancer - target was constructed. The results showed that the probability value of PTPN1 ranked first among all predicted targets, which was consistent with the results of enzyme activity experiments in vitro. The enrichment results of KEGG pathway and GO functional annotation analysis showed that the effect of OA-Br-1 on breast cancer was significantly correlated with the PI3K/AKT pathway. Subsequent Western Blot results also proved that OA-Br-1 could significantly inhibit the expression of PTP1B, p-PI3K and p-AKT, indicating that OA-Br-1 played an anti-breast cancer role through the PTP1B/PI3K/AKT signaling pathway. Collectively, these findings identify OA-Br-1 as a promising PTP1B inhibitor for breast cancer treatment.

Oleanolic acid derivative alleviates cardiac fibrosis through inhibiting PTP1B activity and regulating AMPK/TGF-β/Smads pathway

Cardiac fibrosis (CF) in response to persistent exogenous stimuli or myocardial injury results in cardiovascular diseases (CVDs). Protein tyrosine phosphatase 1B (PTP1B) can promote collagen deposition through regulating AMPK/TGF-β/Smads signaling pathway, and PTP1B knockout improves cardiac dysfunction against overload-induced heart failure. Oleanolic acid (OA) has been proven to be an inhibitor of PTP1B, and its anti-cardiac remodeling effects have been validated in different mouse models. To improve the bioactivity of OA and to clarify whether OA derivatives with stronger inhibition of PTP1B activity have greater prevention of cardiac remodeling than OA, four new OA derivatives were synthesized and among them, we found that compound B had better effects than OA in inhibiting cardiac fibrosis both in vivo in the isoproterenol (ISO)-induced mouse cardiac fibrosis and in vitro in the TGF-β/ISO-induced 3T3 cells. Combining with the results of molecular docking, surface plasmon resonance and PTP1B activity assay, we reported that OA and compound B directly bound to PTP1B and inhibited its activity, and that compound B showed comparable binding capability but stronger inhibitory effect on PTP1B activity than OA. Moreover, compound B presented much greater effects on AMPK activation and TGF-β/Smads inhibition than OA. Taken together, OA derivative compound B more significantly alleviated cardiac fibrosis than OA through much greater inhibition of PTP1B activity and thus much stronger regulation of AMPK/TGF-β/Smads signaling pathway.

Discovery of Bivalent GalNAc-Conjugated Betulin as a Potent ASGPR-Directed Agent against Hepatocellular Carcinoma

Herein, we describe the design, synthesis, and biological evaluation of novel betulin and N-acetyl-d-galactosamine (GalNAc) glycoconjugates and suggest them as targeted agents against hepatocellular carcinoma. We prepared six conjugates derived via the C-3 and C-28 positions of betulin with one or two saccharide ligands. These molecules demonstrate high affinity to the asialoglycoprotein receptor (ASGPR) of hepatocytes assessed by in silico modeling and surface plasmon resonance tests. Cytotoxicity studies in vitro revealed a bivalent conjugate with moderate activity, selectivity of action, and cytostatic properties against hepatocellular carcinoma cells HepG2. An additional investigation confirmed the specific engagement with HepG2 cells by the enhanced generation of reactive oxygen species. Stability tests demonstrated its lability to acidic media and to intracellular enzymes. Therefore, the selected bivalent conjugate represents a new potential agent targeted against hepatocellular carcinoma. Further extensive studies of the cellular uptake in vitro and the real-time microdistribution in the murine liver in vivo for fluorescent dye-labeled analogue showed its selective internalization into hepatocytes due to the presence of GalNAc ligand in comparison with reference compounds. The betulin and GalNAc glycoconjugates can therefore be considered as a new strategy for developing therapeutic agents based on natural triterpenoids.

Flavonoids, terpenoids, and polyketide antibiotics: Role of glycosylation and biocatalytic tactics in engineering glycosylation

Flavonoids, terpenoids, and polyketides are structurally diverse secondary metabolites used widely as pharmaceuticals and nutraceuticals. Most of these molecules exist in nature as glycosides, in which sugar residues act as a decisive factor in their architectural complexity and bioactivity. Engineering glycosylation through selective trimming or extension of the sugar residues in these molecules is a prerequisite to their commercial production as well to creating novel derivatives with specialized functions. Traditional chemical glycosylation methods are tedious and can offer only limited end-product diversity. New in vitro and in vivo biocatalytic tools have emerged as outstanding platforms for engineering glycosylation in these three classes of secondary metabolites to create a large repertoire of versatile glycoprofiles. As knowledge has increased about secondary metabolite-associated promiscuous glycosyltransferases and sugar biosynthetic machinery, along with phenomenal progress in combinatorial biosynthesis, reliable industrial production of unnatural secondary metabolites has gained momentum in recent years. This review highlights the significant role of sugar residues in naturally occurring flavonoids, terpenoids, and polyketide antibiotics. General biocatalytic tools used to alter the identity and pattern of sugar molecules are described, followed by a detailed illustration of diverse strategies used in the past decade to engineer glycosylation of these valuable metabolites, exemplified with commercialized products and patents. By addressing the challenges involved in current bio catalytic methods and considering the perspectives portrayed in this review, exceptional drugs, flavors, and aromas from these small molecules could come to dominate the natural-product industry.

Multiple machine learning based descriptive and predictive workflow for the identification of potential PTP1B inhibitors

In insulin and leptin signaling pathway, Protein-Tyrosine Phosphatase 1B (PTP1B) plays a crucial controlling role as a negative regulator, which makes it an attractive therapeutic target for both Type-2 Diabetes (T2D) and obesity. In this work, we have generated classification models by using the inhibition data set of known PTP1B inhibitors to identify new inhibitors of PTP1B utilizing multiple machine learning techniques like naïve Bayesian, random forest, support vector machine and k-nearest neighbors, along with structural fingerprints and selected molecular descriptors. Several models from each algorithm have been constructed and optimized, with the different combination of molecular descriptors and structural fingerprints. For the training and test sets, most of the predictive models showed more than 90% of overall prediction accuracies. The best model was obtained with support vector machine approach and has Matthews Correlation Coefficient of 0.82 for the external test set, which was further employed for the virtual screening of Maybridge small compound database. Five compounds were subsequently selected for experimental assay. Out of these two compounds were found to inhibit PTP1B with significant inhibitory activity in in-vitro inhibition assay. The structural fragments which are important for PTP1B inhibition were identified by naïve Bayesian method and can be further exploited to design new molecules around the identified scaffolds. The descriptive and predictive modeling strategy applied in this study is capable of identifying PTP1B inhibitors from the large compound libraries.

Recent advances in the development of protein tyrosine phosphatase 1B inhibitors for Type 2 diabetes

Diabetes mellitus is the most serious and prevalent metabolic disorders worldwide, complications of which can decrease significantly the quality of life and contribute to premature death. Resistance to insulin is a predominant pathophysiological factor of Type 2 diabetes (T2D). Protein tyrosine phosphatase 1B (PTP1B) is an important negative factor of insulin signal and a potent therapeutic target in T2D patients. This review highlights recent advances (2012-2015) in research related to the role of PTP1B in signal transduction processes implicated in pathophysiology of T2D, and novel PTP1B inhibitors with an emphasis on their chemical structures and modes of action.

Concise synthesis of a new triterpenoid saponin from the roots of Gypsophila oldhamiana and its derivatives as α-glucosidase inhibitors

The natural triterpenoid saponin 1 and its derivatives 2–3 were synthesized and exhibited potent inhibitory activities against α-glucosidase in vitro.

Synthesis and Evaluation of a Series of Oleanolic Acid Saponins as α-Glucosidase and α-Amylase Inhibitors

Sixteen naturally occurring oleanolic acid saponins and their derivatives were synthesized in an efficient and practical strategy, and their inhibitory activities against α-glucosidase and α-amylase were evaluated in vitro. Among all the compounds, 28-O-monoglucoside 8 exhibited remarkably potent inhibitory activity against α-glucosidase with an IC50 value of 87.3 µM, which was fivefold stronger than that of the antidiabetic acarbose. Based on the preliminary structure-activity relationships, for 28-O-monoglucosides, the presence of a terminal α-l-rhamnopyranosyl residue enhanced the α-glucosidase and α-amylase inhibitory activities. Furthermore, for 3,28-O-bidesmosides, sugar-substituted moieties attached to the C-3 and C-28 positions of the oleanolic acid scaffold are helpful to increase the inhibitory activities against α-amylase and α-glucosidase.

Natural and semisynthetic protein tyrosine phosphatase 1B (PTP1B) inhibitors as anti-diabetic agents

Natural products offered more opportunities to develop new drugs and leading compounds as potent PTP1B inhibitors for treating T2DM.