Valentina Sepe

Homophymine A, an Anti-HIV Cyclodepsipeptide from the Sponge Homophymia sp

A new anti-HIV cyclodepsipeptide, homophymine A, was isolated from a New Caledonian collection of the marine sponge Homophymia sp. The structure of homophymine A was determined by interpretation of spectroscopic data, acid hydrolysis, and LC-MS analysis. Homophymine A contains 11 amino acid residues and an amide-linked 3-hydroxy-2,4,6-trimethyloctanoic acid moiety. Along with four D-, two L-, and one N-methyl amino acids, it also contains four unusual amino acid residues: (2S,3S,4R)-3,4-diMe-Gln, (2R,3R,4S)-4-amino-2,3-dihydroxy-1,7-heptandioic acid, L-ThrOMe, and (2R,3R,4R)-2-amino-3-hydroxy-4,5-dimethylhexanoic acid. In a cell-based XTT assay, homophymine A exhibited cytoprotective activity against HIV-1 infection with a IC50 of 75 nM.

Solomonamides A and B, New Anti-inflammatory Peptides from Theonella swinhoei

Two unprecedented cyclic peptides, solomonamides A and B, were isolated from the marine sponge Theonella swinhoei. The structures were elucidated on the basis of comprehensive 1D and 2D NMR analysis and high-resolution mass spectrometry. A combined approach, involving Marfeys method, QM J based analysis, and DFT J/(13)C calculations, was used for establishing the absolute configuration of the entire molecule. Solomonamide A showed in vivo anti-inflammatory activity.

Discovery that theonellasterol a marine sponge sterol is a highly selective FXR antagonist that protects against liver injury in cholestasis.

Background The farnesoid-x-receptor (FXR) is a bile acid sensor expressed in the liver and gastrointestinal tract. Despite FXR ligands are under investigation for treatment of cholestasis, a biochemical condition occurring in a number of liver diseases for which available therapies are poorly effective, mice harboring a disrupted FXR are protected against liver injury caused by bile acid overload in rodent models of cholestasis. Theonellasterol is a 4-methylene-24-ethylsteroid isolated from the marine sponge Theonella swinhoei. Here, we have characterized the activity of this theonellasterol on FXR-regulated genes and biological functions. Principal Findings Interrogation of HepG2 cells, a human hepatocyte cell line, by microarray analysis and transactivation assay shows that theonellasterol is a selective FXR antagonist, devoid of any agonistic or antagonistic activity on a number of human nuclear receptors including the vitamin D receptor, PPARs, PXR, LXRs, progesterone, estrogen, glucorticoid and thyroid receptors, among others. Exposure of HepG2 cells to theonellasterol antagonizes the effect of natural and synthetic FXR agonists on FXR-regulated genes, including SHP, OSTα, BSEP and MRP4. A proof-of-concept study carried out to investigate whether FXR antagonism rescues mice from liver injury caused by the ligation of the common bile duct, a model of obstructive cholestasis, demonstrated that theonellasterol attenuates injury caused by bile duct ligation as measured by assessing serum alanine aminostrasferase levels and extent of liver necrosis at histopathology. Analysis of genes involved in bile acid uptake and excretion by hepatocytes revealed that theonellasterol increases the liver expression of MRP4, a basolateral transporter that is negatively regulated by FXR. Administering bile duct ligated mice with an FXR agonist failed to rescue from liver injury and downregulated the expression of MRP4. Conclusions FXR antagonism in vivo results in a positive modulation of MRP4 expression in the liver and is a feasible strategy to target obstructive cholestasis.

Design, Synthesis, and Biological Evaluation of Potent Dual Agonists of Nuclear and Membrane Bile Acid Receptors

Bile acids exert genomic and nongenomic effects by interacting with membrane G-protein-coupled receptors, including the bile acid receptor GP-BAR1, and nuclear receptors, such as the farnesoid X receptor (FXR). These receptors regulate overlapping metabolic functions; thus, GP-BAR1/FXR dual agonists, by enhancing the biological response, represent an innovative strategy for the treatment of enteroendocrine disorders. Here, we report the design, total synthesis, and in vitro/in vivo pharmacological evaluation of a new generation of dual bile acid receptor agonists, with the most potent compound, 19, showing promising pharmacological profiles. We show that compound 19 activates GP-BAR1, FXR, and FXR regulated genes in the liver, increases the intracellular concentration of cAMP, and stimulates the release of the potent insulinotropic hormone GLP-1, resulting in a promising drug candidate for the treatment of metabolic disorders. We also elucidate the binding mode of the most potent dual agonists in the two receptors through a series of computations providing the molecular basis for dual GP-BAR1/FXR agonism.

Exploitation of Cholane Scaffold for the Discovery of Potent and Selective Farnesoid X Receptor (FXR) and G-Protein Coupled Bile Acid Receptor 1 (GP-BAR1) Ligands

Nuclear and G-protein coupled receptors are considered major targets for drug discovery. FXR and GP-BAR1, two bile acid-activated receptors, have gained increasing consideration as druggable receptors. Because endogenous bile acids often target both receptor families, the development of selective ligands has been proven difficult, exposing patients to side effects linked to an unwanted activation of one of the two receptors. In the present study, we describe a novel library of semisynthetic bile acid derivatives obtained by modifications on the cholane scaffold. The pharmacological characterization of this library led to the discovery of 7α-hydroxy-5β-cholan-24-sulfate (7), 6β-ethyl-3α,7β-dihydroxy-5β-cholan-24-ol (EUDCOH, 26), and 6α-ethyl-3α, 7α-dihydroxy-24-nor-5β-cholan-23-ol (NorECDCOH, 30) as novel ligands for FXR and GP-BAR1 that might hold utility in the treatment of FXR and GP-BAR1 mediated disorders.

Modification on Ursodeoxycholic Acid (UDCA) Scaffold. Discovery of Bile Acid Derivatives As Selective Agonists of Cell-Surface G-Protein Coupled Bile Acid Receptor 1 (GP-BAR1)

Bile acids are signaling molecules interacting with the nuclear receptor FXR and the G-protein coupled receptor 1 (GP-BAR1/TGR5). GP-BAR1 is a promising pharmacological target for the treatment of steatohepatitis, type 2 diabetes, and obesity. Endogenous bile acids and currently available semisynthetic bile acids are poorly selective toward GP-BAR1 and FXR. Thus, in the present study we have investigated around the structure of UDCA, a clinically used bile acid devoid of FXR agonist activity, to develop a large family of side chain modified 3α,7β-dihydroxyl cholanoids that selectively activate GP-BAR1. In vivo and in vitro pharmacological evaluation demonstrated that administration of compound 16 selectively increases the expression of pro-glucagon 1, a GP-BAR1 target, in the small intestine, while it had no effect on FXR target genes in the liver. Further, compound 16 results in a significant reshaping of bile acid pool in a rodent model of cholestasis. These data demonstrate that UDCA is a useful scaffold to generate novel and selective steroidal ligands for GP-BAR1.

Stereochemical assignment of the C23-C35 portion of sphinxolide/reidispongiolide class of natural products by asymmetric synthesis

Abstract The absolute configuration of the seven stereogenic centers contained in the C23–C35 portion of reidispongiolide A is determined by asymmetric synthesis of the corresponding fragment obtained by ozonolysis of the natural macrolide.

Synthetic and pharmacological studies on new simplified analogues of the potent actin-targeting Jaspamide

In the recent years, we focused our attention on the cyclodepsipeptide Jaspamide 1, an interesting marine metabolite, possessing a potent inhibitory activity against breast and prostate cancer, as a consequence of its ability to disrupt actin cytoskeleton dynamics. Although its biological profile has been well determined, many mechanistic details are still missing in terms of molecular target identification. For this reason, we decided to synthetically modify the natural metabolite, obtaining small arrays of unnatural variants useful to illuminate the structural requirements essential for the activity. Here, we report the synthesis of seven new Jaspamide analogues 2-8, containing, as the parent compound, a beta-amino acid in the cyclopeptide backbone. Their biological profile is also described.

Natural Ligands for Nuclear Receptors: Biology and Potential Therapeutic Applications

Nuclear receptors are key regulators of various processes including reproduction, development, and metabolism of xeno- and endobiotics. Research in the last two decades has focused to the development of novel drugs specifically targeting nuclear receptors for the treatment of a variety of diseases, such as cancer, diabetes, dyslipidemia, fatty liver disease, drug hepatotoxicity and cholestasis. The search for novel NRs agonists and antagonists with enhanced selectivity prompted the exploration of the extraordinary chemical diversity associated to natural products. In recent years a number of natural products were disclosed as ligands of NRs and proved to have remarkable affinity and in some cases peculiar mode of action. In this review the natural ligands of the subfamily NR1, NR2, and NR3 will be described with an emphasis to their mechanisms of action and pharmacological profiles.

Insights on FXR selective modulation. Speculation on bile acid chemical space in the discovery of potent and selective agonists.

Bile acids are the endogenous modulators of the nuclear receptor FXR and the membrane receptor GPBAR1. FXR represents a promising pharmacological target for the treatment of cholestatic liver disorders. Currently available semisynthetic bile acid derivatives cover the same chemical space of bile acids and therefore they are poorly selective toward BA receptors, increasing patient risk for adverse side effects. In this report, we have investigated around the structure of CDCA describing the synthesis and the in vitro and in vivo pharmacological characterization of a novel family of compounds modified on the steroidal tetracyclic core and on the side chain. Pharmacological characterization resulted in the identification of several potent and selective FXR agonists. These novel agents might add utility in the treatment of cholestatic disorders by potentially mitigating side effects linked to unwanted activation of GPBAR1.