Two dedicated receptors for bile acids (BAs) have been identified, the nuclear hormone receptor farnesoid X receptor (FXR) and the G protein-coupled receptor TGR5, which represent attractive targets for the treatment of metabolic and chronic liver diseases. Previous work characterized 6␣-ethyl-3␣,7␣-dihydroxy-5␤-cholan-24-oic acid (INT-747), a potent and selective FXR agonist, as well as 6␣-ethyl-23(S)-methyl-3␣,7␣,12␣-trihydroxy-5␤-cholan-24-oic acid (INT-777), a potent and selective TGR5 agonist. Here we characterize 6␣-ethyl-3␣,7␣,23-trihydroxy-24-nor-5␤-cholan-23-sulfate sodium salt (INT-767), a novel semisynthetic 23-sulfate derivative of INT-747. INT-767 is a potent agonist for both FXR (mean EC 50 , 30 nM by PerkinElmer AlphaScreen assay) and TGR5 (mean EC 50 , 630 nM by time resolved-fluorescence resonance energy transfer), the first compound described so far to potently and selectively activate both BA receptors.INT-767 does not show cytotoxic effects in HepG2 cells, does not inhibit cytochrome P450 enzymes, is highly stable to phase I and II enzymatic modifications, and does not inhibit the human ether-a-go-go-related gene potassium channel. In line with its dual activity, INT-767 induces FXRdependent lipid uptake by adipocytes, with the beneficial effect of shuttling lipids from central hepatic to peripheral fat storage, and promotes TGR5-dependent glucagon-like peptide-1 secretion by enteroendocrine cells, a validated target in the treatment of type 2 diabetes. Moreover, INT-767 treatment markedly decreases cholesterol and triglyceride levels in diabetic db/db mice and in mice rendered diabetic by streptozotocin administration. Collectively, these preclinical results indicate that INT-767 is a safe and effective modulator of FXR and TGR5-dependent pathways, suggesting potential clinical applications in the treatment of liver and metabolic diseases.

Retinol and vitamin A derivatives influence cell differentiation, proliferation, and apoptosis and play an important physiologic role in a wide range of biological processes. Retinol is obtained from foods of animal origin. Retinol derivatives are fundamental for vision, while retinoic acid is essential for skin and bone growth. Intracellular retinoid bioavailability is regulated by the presence of specific cytoplasmic retinol and retinoic acid binding proteins (CRBPs and CRABPs). CRBP-1, the most diffuse CRBP isoform, is a small 15 KDa cytosolic protein widely expressed and evolutionarily conserved in many tissues. CRBP-1 acts as chaperone and regulates the uptake, subsequent esterification, and bioavailability of retinol. CRBP-1 plays a major role in wound healing and arterial tissue remodelling processes. In the last years, the role of CRBP-1-related retinoid signalling during cancer progression became object of several studies. CRBP-1 downregulation associates with a more malignant phenotype in breast, ovarian, and nasopharyngeal cancers. Reexpression of CRBP-1 increased retinol sensitivity and reduced viability of ovarian cancer cells in vitro. Further studies are needed to explore new therapeutic strategies aimed at restoring CRBP-1-mediated intracellular retinol trafficking and the meaning of CRBP-1 expression in cancer patients' screening for a more personalized and efficacy retinoid therapy.

New anti-telomere strategies represent important goals for the development of selective cancer therapies. In this study, we reported that uncapped telomeres, resulting from pharmacological stabilization of quadruplex DNA by RHPS4 (3,11-difluoro-6,8,13-trimethyl-8H-quino [4,3,2-kl]acridinium methosulfate), trigger specific recruitment and activation of poly-adenosine diphosphate (ADP) ribose polymerase I (PARP1) at the telomeres, forming several ADP-ribose polymers that co-localize with the telomeric repeat binding factor 1 protein and are inhibited by selective PARP(s) inhibitors or PARP1-specific small interfering RNAs. The knockdown of PARP1 prevents repairing of RHPS4-induced telomere DNA breaks, leading to increases in chromosome abnormalities and eventually to the inhibition of tumor cell growth both in vitro and in xenografts. More interestingly, the integration of a TOPO1 inhibitor on the combination treatment proved to have a high therapeutic efficacy ensuing a complete regression of the tumor as well as a significant increase in overall survival and cure of mice even when treatments started at a very late stage of tumor growth. Overall, this work reveals the unexplored link between the PARP1 and G-quadruplex ligands and demonstrates the excellent efficacy of a multicomponent strategy based on the use of PARP inhibitors in telomere-based therapy.

Sirt2 is a target for the treatment of neurological, metabolic, and age-related diseases including cancer. Here we report a series of Sirt2 inhibitors based on the 1,2,4-oxadiazole scaffold. These compounds are potent Sirt2 inhibitors active at single-digit μM level by using the Sirt2 substrate α-tubulin-acetylLys40 peptide and inactive up to 100 μM against Sirt1, -3, and -5 (deacetylase and desuccinylase activities). Their mechanism of inhibition is uncompetitive toward both the peptide substrate and NAD, and the crystal structure of a 1,2,4-oxadiazole analog in complex with Sirt2 and ADP-ribose reveals its orientation in a still unexplored subcavity useful for further inhibitor development. Tested in leukemia cell lines, 35 and 39 induced apoptosis and/or showed antiproliferative effects at 10 or 25 μM after 48 h. Western blot analyses confirmed the involvement of Sirt2 inhibition for their effects in NB4 and in U937 cells. Our results provide novel Sirt2 inhibitors with a compact scaffold and structural insights for further inhibitor improvement.

BACKGROUND AND PURPOSEBrain natriuretic peptide (BNP) plays an important role in several biological functions, including bronchial relaxation. Here, we have investigated the role of BNP and its cognate receptors in human bronchial tone. EXPERIMENTAL APPROACHEffects of BNP on responses to carbachol and histamine were evaluated in non-sensitized, passively sensitized, epitheliumintact or denuded isolated bronchi and in the presence of methoctramine, N w -nitro-L-arginine methyl ester (L-NAME) and aminoguanidine. Natriuretic peptide receptors (NPRs) were investigated by immunohistochemistry, RT-PCR and real-time PCR. Release of NO and acetylcholine from bronchial tissues and cultured BEAS-2B bronchial epithelial cells was also investigated. KEY RESULTSBNP reduced contractions mediated by carbachol and histamine, with decreased Emax (carbachol: 22.7 Ϯ 4.7%; histamine: 59.3 Ϯ 1.8%) and increased EC50 (carbachol: control 3.33 Ϯ 0.88 mM, BNP 100 Ϯ 52.9 mM; histamine: control 16.7 Ϯ 1.7 mM, BNP 90 Ϯ 30.6 mM); BNP was ineffective in epithelium-denuded bronchi. Among NPRs, only atrial NPR (NPR1) transcripts were detected in bronchial tissue. Bronchial NPR1 immunoreactivity was detected in epithelium and inflammatory cells but faint or absent in airway smooth muscle cells. NPR1 transcripts in bronchi increased after incubation with BNP, but not after sensitization. Methoctramine and quinine abolished BNP-induced relaxant activity. The latter was associated with increased bronchial mRNA for NO synthase and NO release, inhibited by L-NAME and aminoguanidine. In vitro, BNP increased acetylcholine release from bronchial epithelial cells, whereas NO release was unchanged. CONCLUSIONS AND IMPLICATIONSEpithelial cells mediate the BNP-induced relaxant activity in human isolated bronchi. AbbreviationsASM, airway smooth muscle; BNP, brain natriuretic peptide; COPD, chronic obstructive pulmonary disease; E, effect; Emax, maximal response; eNOS, endothelial nitric oxide synthase; iNOS, inducible nitric oxide synthase; KH, KrebsHenseleit buffer solution; L-NAME, N w -nitro-L-arginine methyl ester hydrochloride; MTT, 3-[4,5-dimethylthiazol-2-yl]2,5-diphenyl tetrazolium bromide; NPR, natriuretic peptide receptor; pGC, particulate guanylate cyclase; Ki, receptor binding affinity BJP British Journal of Pharmacology

The farnesoid X receptor (FXR) is a nuclear receptor that functions as an endogenous sensor for bile acids (BAs). FXR is bound to and activated by bile acid, and chenodeoxycholic acid (CDCA) is the natural most active ligand. Upon activation, FXR heterodimerizes with the 9-cis retinoic X receptor (RXR) and regulates genes involved in cholesterol and BA homeostasis. 6-Ethyl CDCA (6-ECDCA) is a synthetic BA that binds FXR and induces gene transcription by recruiting coactivators, such as steroid receptor coactivator-1, with histone acetyltransferase activity. In addition to acetylation, histone methylation is critically involved in regulating eukaryotic gene expression. In the present study, we demonstrated that 6-ECDCA activates FXR to interacts with Protein Arginine Methyl-Transferase type I (PRMT1), which induces up-regulation of bile salt export pump (BSEP) and the small heterodimer partner (SHP) mRNA expression and causes a down-regulation of P450 cholesterol 7␣-hydroxylase and Na ϩ taurocholate cotransport peptide genes. Chromatin immunoprecipitation assay suggests that 6-ECDCA induces both the recruitment of PRMT1 and the H4 methylation to the promoter of BSEP and SHP genes. We also provide evidence that a methyltransferase inhibitor blocks the activation of FXR-responsive genes. Our results indicate that histone methylation, similar to acetylation, regulates transcriptional activation of genes involved in cholesterol and BAs homeostasis.

Retinoic acid controls hematopoietic differentiation through the transcription factor activity of its receptors. They act on specific target genes by recruiting protein complexes that deacetylate or acetylate histones and modify chromatin status. The regulation of this process is affected by histone methyltransferases, which can inhibit or activate transcription depending on their amino acid target. We show here that retinoic acid treatment of hematopoietic cells induces the expression of BTG2. Overexpression of this protein increases RAR␣ transcriptional activity and the differentiation response to retinoic acid of myeloid leukemia cells and CD34 ؉ hematopoietic progenitors. In the absence of retinoic acid, BTG2 is present in the RAR␣ transcriptional complex, together with the arginine methyltransferase PRMT1 and Sin3A. Overexpressed BTG2 increases PRMT1 participation in the RAR␣ protein complex on the RAR␤ promoter, a target gene model, and enhances gene-specific histone H4 arginine methylation. Upon RA treatment Sin3A, BTG2, and PRMT1 detach from RAR␣ and thereafter BGT2 and PRMT1 are driven to the cytoplasm. These events prime histone H4 demethylation and acetylation. Overall, our data show that BTG2 contributes to retinoic acid activity by favoring differentiation through a gene-specific modification of histone H4 arginine methylation and acetylation levels.

The mitogen-activated protein kinase (MAPK) and PI3K pathways are regulated by extensive crosstalk, occurring at different levels. In tumors, transactivation of the alternate pathway is a frequent "escape" mechanism, suggesting that combined inhibition of both pathways may achieve synergistic antitumor activity. Here we show that, in the M14 melanoma model, simultaneous inhibition of both MEK and mammalian target of rapamycin (mTOR) achieves synergistic effects at suboptimal concentrations, but becomes frankly antagonistic in the presence of relatively high concentrations of MEK inhibitors. This observation led to the identification of a novel crosstalk mechanism, by which either pharmacologic or genetic inhibition of constitutive MEK signaling restores phosphatase and tensin homolog (PTEN) expression, both in vitro and in vivo, and inhibits downstream signaling through AKT and mTOR, thus bypassing the need for double pathway blockade. This appears to be a general regulatory mechanism and is mediated by multiple mechanisms, such as MAPK-dependent c-Jun and miR-25 regulation. Finally, PTEN upregulation appears to be a major effector of MEK inhibitors' antitumor activity, as cancer cells in which PTEN is inactivated are consistently more resistant to the growth inhibitory and anti-angiogenic effects of MEK blockade.