PHA-680626 Is an Effective Inhibitor of the Interaction between Aurora-A and N-Myc.

Neuroblastoma is a severe childhood disease, accounting for ~10% of all infant cancers. The amplification of the MYCN gene, coding for the N-Myc transcription factor, is an essential marker correlated with tumor progression and poor prognosis. In neuroblastoma cells, the mitotic kinase Aurora-A (AURKA), also frequently overexpressed in cancer, prevents N-Myc degradation by directly binding to a highly conserved N-Myc region. As a result, elevated levels of N-Myc are observed. During recent years, it has been demonstrated that some ATP competitive inhibitors of AURKA also cause essential conformational changes in the structure of the activation loop of the kinase that prevents N-Myc binding, thus impairing the formation of the AURKA/N-Myc complex. In this study, starting from a screening of crystal structures of AURKA in complexes with known inhibitors, we identified additional compounds affecting the conformation of the kinase activation loop. We assessed the ability of such compounds to disrupt the interaction between AURKA and N-Myc in vitro, using Surface Plasmon Resonance competition assays, and in tumor cell lines overexpressing MYCN, by performing Proximity Ligation Assays. Finally, their effects on N-Myc cellular levels and cell viability were investigated. Our results identify PHA-680626 as an amphosteric inhibitor both in vitro and in MYCN overexpressing cell lines, thus expanding the repertoire of known conformational disrupting inhibitors of the AURKA/N-Myc complex and confirming that altering the conformation of the activation loop of AURKA with a small molecule is an effective strategy to destabilize the AURKA/N-Myc interaction in neuroblastoma cancer cells.

Bromodomain and extraterminal (BET) proteins regulate biliary-driven liver regeneration.

BACKGROUND & AIMS: During liver regeneration, hepatocytes are derived from pre-existing hepatocytes. However, if hepatocyte proliferation is compromised, biliary epithelial cells (BECs) become the source of new hepatocytes. We recently reported on a zebrafish liver regeneration model in which BECs extensively contribute to hepatocytes. Using this model, we performed a targeted chemical screen to identify important factors that regulate BEC-driven liver regeneration, the mechanisms of which remain largely unknown. METHODS: Using Tg(fabp10a:CFP-NTR) zebrafish, we examined the effects of 44 selected compounds on BEC-driven liver regeneration. Liver size was assessed by fabp10a:DsRed expression; liver marker expression was analyzed by immunostaining, in situ hybridization and quantitative PCR. Proliferation and apoptosis were also examined. Moreover, we used a mouse liver injury model, choline-deficient, ethionine-supplemented (CDE) diet. RESULTS: We identified 10 compounds that affected regenerating liver size. Among them, only bromodomain and extraterminal domain (BET) inhibitors, JQ1 and iBET151, blocked both Prox1 and Hnf4a induction in BECs. BET inhibition during hepatocyte ablation blocked BEC dedifferentiation into hepatoblast-like cells (HB-LCs). Intriguingly, after JQ1 washout, liver regeneration resumed, indicating temporal, but not permanent, perturbation of liver regeneration by BET inhibition. BET inhibition after hepatocyte ablation suppressed the proliferation of newly generated hepatocytes and delayed hepatocyte maturation. Importantly, Myca overexpression, in part, rescued the proliferation defect. Furthermore, oval cell numbers in mice fed CDE diet were greatly reduced upon JQ1 administration, supporting the zebrafish findings. CONCLUSIONS: BET proteins regulate BEC-driven liver regeneration at multiple steps: BEC dedifferentiation, HB-LC proliferation, the proliferation of newly generated hepatocytes, and hepatocyte maturation.

Pyrido-imidazodiazepinones as a new class of reversible inhibitors of human kallikrein 7.

The human tissue kallikrein-7 (KLK7) is a chymotryptic serine protease member of tissue kallikrein family. KLK7 is involved in skin homeostasis and inflammation. Excess of KLK7 activity is also associated with tumor metastasis processes, especially in ovarian carcinomas, prostatic and pancreatic cancers. Development of Kallikrein 7 inhibitors is thus of great interest in oncology but also for treating skin diseases. Most of the developed synthetic inhibitors present several drawbacks such as poor selectivity and unsuitable physico-chemical properties for in vivo use. Recently, we described a practical sequence for the synthesis of imidazopyridine-fused [1,3]-diazepines. Here, we report the identification of pyrido-imidazodiazepinone core as a new potential scaffold to develop selective and competitive inhibitors of kallikrein-related peptidase 7. Structure-activity relationships (SAR), inhibition mechanisms and selectivity as well as cytotoxicity against selected cancer cell lines were investigated.

Production of therapeutically relevant indolizidine alkaloids in Securinega suffruticosa in vitro shoots maintained in liquid culture systems.

Microshoot cultures of the Chinese medicinal plant Securinega suffruticosa (Pall.) Rehd. were established and evaluated for the presence of therapeutically relevant indolizidine alkaloids securinine (S) and allosecurinine (AS). The cultures were maintained in shake flasks (SFs) and a bubble column bioreactor (BCB) using the modified Murashige's shoot multiplication medium supplemented with 1.0 mg l(-1) benzyladenine (BA), 3.0 mg l(-1) 2-isopentenyladenine (2iP), and 0.3 mg l(-1) 1-naphthaleneacetic acid (NAA). The influence of light and medium supplementation strategies with biosynthesis precursor (lysine (LY)) and nutrient formulations (casein hydrolysate (CH) and coconut water (CW)) on biomass growth and alkaloid production were investigated. SF cultures grown in the presence of light yielded up to 6.02 mg g(-1) dry weight (DW) S and 3.70 mg g(-1) DW AS, corresponding to the respective productivities of 98.39 and 60.21 mg l(-1). Among feeding experiments, CW supplementation proved most effective for SF-grown shoots, increasing biomass yield and AS productivity by 52 and 44 %, respectively. Maximum concentrations of securinine (3.25 mg g(-1) DW) and allosecurinine (3.41 mg g(-1) DW) in BCB cultures were achieved in the case of 1.0 g l(-1) LY supplementation. These values corresponded to the productivities of 42.64 and 44.47 mg per bioreactor, respectively.

Successful prediction of substrate-binding pocket in SLC17 transporter sialin.

Secondary active transporters from the SLC17 protein family are required for excitatory and purinergic synaptic transmission, sialic acid metabolism, and renal function, and several members are associated with inherited neurological or metabolic diseases. However, molecular tools to investigate their function or correct their genetic defects are limited or absent. Using structure-activity, homology modeling, molecular docking, and mutagenesis studies, we have located the substrate-binding site of sialin (SLC17A5), a lysosomal sialic acid exporter also recently implicated in exocytotic release of aspartate. Human sialin is defective in two inherited sialic acid storage diseases and is responsible for metabolic incorporation of the dietary nonhuman sialic acid N-glycolylneuraminic acid. We built cytosol-open and lumen-open three-dimensional models of sialin based on weak, but significant, sequence similarity with the glycerol-3-phosphate and fucose permeases from Escherichia coli, respectively. Molecular docking of 31 synthetic sialic acid analogues to both models was consistent with inhibition studies. Narrowing the sialic acid-binding site in the cytosol-open state by two phenylalanine to tyrosine mutations abrogated recognition of the most active analogue without impairing neuraminic acid transport. Moreover, a pilot virtual high-throughput screening of the cytosol-open model could identify a pseudopeptide competitive inhibitor showing >100-fold higher affinity than the natural substrate. This validated model of human sialin and sialin-guided models of other SLC17 transporters should pave the way for the identification of inhibitors, glycoengineering tools, pharmacological chaperones, and fluorescent false neurotransmitters targeted to these proteins.

Binding of 3,4,5,6-tetrahydroxyazepanes to the acid-ß-glucosidase active site: implications for pharmacological chaperone design for Gaucher disease.

Pharmacologic chaperoning is a therapeutic strategy being developed to improve the cellular folding and trafficking defects associated with Gaucher disease, a lysosomal storage disorder caused by point mutations in the gene encoding acid-ß-glucosidase (GCase). In this approach, small molecules bind to and stabilize mutant folded or nearly folded GCase in the endoplasmic reticulum (ER), increasing the concentration of folded, functional GCase trafficked to the lysosome where the mutant enzyme can hydrolyze the accumulated substrate. To date, the pharmacologic chaperone (PC) candidates that have been investigated largely have been active site-directed inhibitors of GCase, usually containing five- or six-membered rings, such as modified azasugars. Here we show that a seven-membered, nitrogen-containing heterocycle (3,4,5,6-tetrahydroxyazepane) scaffold is also promising for generating PCs for GCase. Crystal structures reveal that the core azepane stabilizes GCase in a variation of its proposed active conformation, whereas binding of an analogue with an N-linked hydroxyethyl tail stabilizes GCase in a conformation in which the active site is covered, also utilizing a loop conformation not seen previously. Although both compounds preferentially stabilize GCase to thermal denaturation at pH 7.4, reflective of the pH in the ER, only the core azepane, which is a mid-micromolar competitive inhibitor, elicits a modest increase in enzyme activity for the neuronopathic G202R and the non-neuronopathic N370S mutant GCase in an intact cell assay. Our results emphasize the importance of the conformational variability of the GCase active site in the design of competitive inhibitors as PCs for Gaucher disease.

Impact of physicochemical and structural properties on the pharmacokinetics of a series of alpha1L-adrenoceptor antagonists.

A rational drug discovery process was initiated to design a potent and prostate-selective alpha1(L)-adrenoceptor antagonist with pharmacokinetic properties suitable for once a day administration after oral dosing, for the treatment of benign prostatic hyperplasia. Two series of compounds based on a quinoline or quinazoline template were identified with appropriate pharmacology. A series of high molecular weight cations with high hydrogen-bonding potential had extensive in vivo clearance, despite demonstrating metabolic stability. Studies in the isolated perfused rat liver and fresh rat hepatocytes indicated that active transport protein-mediated hepatobiliary elimination is an efficient clearance process for these compounds. A reduction in molecular weight and hydrogen-bonding potential resulted in a second series of compounds with in vivo hepatic clearance predictable from in vitro metabolic clearance. Initially, lipophilicity was reduced within this second series to reduce metabolic clearance and increase elimination half-life. However, this strategy also resulted in a concomitant reduction in volume of distribution and a negligible effect on prolonging half-life. An alternative strategy was to increase the intrinsic metabolic stability of the molecule by careful structural modifications while maintaining lipophilicity. Replacement of the metabolically vulnerable morpholine side chain resulted in identification of UK-338,003, (N-[2-(4-amino-6,7-dimethoxy-5-pyridin-2-yl-quinazolin-2-yl)-1,2,3,4-tetrahydro-isoquinolin-5-yl]-methanesulfonamide), which fulfilled the objectives of the discovery program with suitable pharmacology (human prostate alpha1(L) pA(2) of 9.2 with 25-fold selectivity over rat aorta alpha1(D)) and sufficiently long elimination half-life in human volunteers (11-17 h) for once a day administration.

[The metabolic transformation of (-)-securinine].

AIM: To study the in vitro and in vivo metabolism of (-)-securinine. METHODS: The metabolic transformation of (-)-securinine was studied by using phenobarbital-induced rat liver microsomal incubate containing the NADPH-generating system in vitro and the constitution of the system was optimized. A reversed phase HPLC method was established to analyze the parent drug and its metabolites. The major metabolites were isolated and purified by liquid-liquid extraction, preparative TLC and HPLC, and their structures were elucidated as 6-hydroxyl securinine, 6-carbonyl securinine, 5 beta-hydroxyl securinine and 5 alpha-hydroxyl securinine by 1HNMR, 13CNMR and MS spectral analysis. An HPLC method was developed to analyze securinine and its metabolites in biofluids (bile, urine) of rat. The bile, urine and their enzymatic hydrolyzed samples of the rat i.p. administrated with (-)-securinine were determined by using this method. RESULTS: Four main metabolites of (-)-securinine in rat hepatic microsome incubation were obtained and their structures were elucidated. Metabolites from in vitro study were confirmed in biofluids (bile, urine) which were collected from rats given securinine i.p. It was suggested that 6-hydroxyl securinine was excreted in conjugated form as well by analyzing enzymatic hydrolyzed bile. CONCLUSION: The main metabolic pathway of (-)-securinine in vitro and in vivo is basically elucidated.

[Study on the chiral separation of securinine by high-performance capillary electrophoresis and its stereoselective metabolism in rat].

AIM: To establish a high-performance capillary electrophoresis (HPCE) chiral separation method for d-securinine and l-securinine, and use this method to investigate the stereoselective metabolism process of d- and l-securinine in Wistar rats. METHODS: The electrophoretic condition and parameters were investigated and the optimized conditions were as following: the electrophoretic medium was 40 mmol.L-1 Tris-H3PO4 buffer (pH adjusted to 6.0 with H3PO4) containing 32 mmol.L-1 HP-beta-CD as chiral selector. Determination was carried out with a UV detector at 254 nm. The separations were performed at 16 degrees C with a positive voltage of 15 kV. Samples were injected into the capillary by pressure for 6 s. The biological samples (urine, bile, plasma and feces) of rats were alkalized and extracted with ethyl acetate. RESULTS: The experimental results showed that the concentration of HP-beta-CD, the concentration of the running buffer and the pH value of the buffer were the main important factors which effected the resolution. d-Securinine and l-securinine were separated at baseline level under the determination conditions. The determination was not interfered by endogenous components and metabolites. After i.p. administration, the rats excreted more d-securinine than l-securinine through bile, urine and feces. The metabolism process in rats was stereoselective. CONCLUSION: This method is simple, reliable and suitable for studying the stereoselective metabolism of securinine in rats.

Platelet-activating factor receptors in lamb lungs are downregulated immediately after birth.

Platelet-activating factor (PAF) is a phospholipid with diverse biological functions mediated by a G protein-coupled receptor. We determined PAF receptor binding in lung membranes of four groups of perinatal lambs. Membrane protein (100 microg/ml) was incubated for 60 min at 30 degrees C with 0.5-24 nM of acetyl-[(3)H]PAF in 30 mM Tris buffer, pH 7.2, containing 0.25% BSA, 10 mM MgCl(2), and 125 mM choline chloride. PAF bound to membrane was isolated and quantified by scintillation spectrometry, followed with Scatchard analysis for receptor density (B(max)). The B(max) (means +/- SE, fmol/mg protein) were 445.8 +/- 12.3, 244.2 +/- 3.3, 250.6 +/- 3.6, and 419. 9 +/- 8.6 for the fetal, 90-min-old, <1-day-old, and 6- to 12-day-old lambs, respectively. The B(max) for the 90-min-old and <1-day-old lambs were not different but were significantly lower than those of either the term fetal or 6- to 12-day-old lambs. These data show a significant decrease in PAF binding to its receptor and in PAF B(max) in lung membranes of immediate newborn lambs. The dissociation constants (K(D), nM) were 7.7 +/- 0.52, 11.5 +/- 0.34, 6.9 +/- 0.48, and 5.0 +/- 0.53 for fetal, 90-min-old, <1-day-old, and 6- to 12-day-old newborn lamb lungs, respectively. The K(D) of the 90-min-old lamb was the highest of all. PAF receptor gene measured by RT-PCR showed a significant downregulation of PAF receptor gene mRNA in lungs of lambs <1 day old, suggesting a transcriptional regulation of PAF receptor gene expression in the immediate newborn period. We speculate that decreased PAF receptor binding immediately after birth will facilitate the fall in pulmonary vascular resistance in the immediate newborn period.

Expression of human platelet-activating factor receptor gene in EoL-1 cells following butyrate-induced differentiation.

Platelet-activating factor (PAF) is a potent lipid mediator of allergic inflammation through its interaction with eosinophils. Expression of the PAF receptor is modulated by many agents, including those responsible for cell differentiation. We report here that differentiation of a human eosinophilic leukaemia cell line, EoL-1, by sodium n-butyrate is associated with induction of PAF receptor gene expression, as indicated by: PAF receptor mRNA accumulation; increases in the binding of [3H]WEB 2086, a PAF antagonist; analysis of cell-surface expression of PAF receptor protein using a monoclonal anti-(PAF receptor) antibody; and augmentation of PAF-induced increase in the intracellular concentration of calcium. Using cDNA cloning, the receptor expressed in EoL-1 cells was identified as 'Transcript 1', one of two transcripts which was previously reported from human genomic analysis (Mutoh, Bito, Minami, Nakamura, Honda, Izumi, Nakata, Kurachi, Terano and Shimizu (1993) FEBS Lett. 322, 129-134). The PAF-induced calcium response and phosphoinositide turnover were decreased by pertussis toxin (PTX) treatment, suggesting that these signals are coupled largely with PTX-sensitive G-protein(s) in EoL-1 cells. These systems may provide a useful experimental model with which to investigate the relationship between eosinophilic differentiation and PAF receptor induction, and the role of eosinophils in allergic responses.

Rational design of potent, bioavailable, nonpeptide cyclic ureas as HIV protease inhibitors.

Mechanistic information and structure-based design methods have been used to design a series of nonpeptide cyclic ureas that are potent inhibitors of human immunodeficiency virus (HIV) protease and HIV replication. A fundamental feature of these inhibitors is the cyclic urea carbonyl oxygen that mimics the hydrogen-bonding features of a key structural water molecule. The success of the design in both displacing and mimicking the structural water molecule was confirmed by x-ray crystallographic studies. Highly selective, preorganized inhibitors with relatively low molecular weight and high oral bioavailability were synthesized.