Photoactivated gamma-secretase inhibitors directed to the active site covalently label presenilin 1

Cleavage of amyloid precursor protein (APP) by the beta- and gamma-secretases generates the amino and carboxy termini, respectively, of the A beta amyloidogenic peptides A beta40 and A beta42--the major constituents of the amyloid plaques in the brain parenchyma of Alzheimer's disease patients. There is evidence that the polytopic membrane-spanning proteins, presenilin 1 and 2 (PS1 and PS2), are important determinants of gamma-secretase activity: mutations in PS1 and PS2 that are associated with early-onset familial Alzheimer's disease increase the production of A beta42 (refs 4-6), the more amyloidogenic peptide; gamma-secretase activity is reduced in neuronal cultures derived from PS1-deficient mouse embryos; and directed mutagenesis of two conserved aspartates in transmembrane segments of PS1 inactivates the ability of gamma-secretase to catalyse processing of APP within its transmembrane domain. It is unknown, however, whether PS1 (which has little or no homology to any known aspartyl protease) is itself a transmembrane aspartyl protease or a gamma-secretase cofactor, or helps to colocalize gamma-secretase and APP. Here we report photoaffinity labelling of PS1 (and PS2) by potent gamma-secretase inhibitors that were designed to function as transition state analogue inhibitors directed to the active site of an aspartyl protease. This observation indicates that PS1 (and PS2) may contain the active site of gamma-secretase. Interestingly, the intact, single-chain form of wild-type PS1 is not labelled by an active-site-directed photoaffinity probe, suggesting that intact wild-type PS1 may be an aspartyl protease zymogen.

Sedative but not anxiolytic properties of benzodiazepines are mediated by the GABA(A) receptor alpha1 subtype

Inhibitory neurotransmission in the brain is largely mediated by GABA(A) receptors. Potentiation of GABA receptor activation through an allosteric benzodiazepine (BZ) site produces the sedative, anxiolytic, muscle relaxant, anticonvulsant and cognition-impairing effects of clinically used BZs such as diazepam. We created genetically modified mice (alpha1 H101R) with a diazepam-insensitive alpha1 subtype and a selective BZ site ligand, L-838,417, to explore GABA(A) receptor subtypes mediating specific physiological effects. These two complimentary approaches revealed that the alpha1 subtype mediated the sedative, but not the anxiolytic effects of benzodiazepines. This finding suggests ways to improve anxiolytics and to develop drugs for other neurological disorders based on their specificity for GABA(A) receptor subtypes in distinct neuronal circuits.

[Esophageal perforation and postoperative fistulae of the upper digestive tract treated endoscopically with the application of Tissucol]

We present three patients with serious gastro-esophageal complications which were treated with Tissucol. The first patient developed a rare postoperative oesophago-pleural fistula. The second suffered a traumatic esophageal perforation (possibly iatrogenic) that was discovered at the end of the removal procedure of an alimentary bolus impacted in the distal esophagus. Attempts to close the high output oesophago-pleural fistula with standard treatment were unsuccessful. It was closed with Tissucol at the third attempt, in conjunction with oesophago-jejunal stenosis by means of endoscopic dilatation. In the second patient, early Tissucol application after detection of pneumomediastinum was an effective complementary treatment to the conservative approach and rapidly closed the perforation. The third patient developed a low debit postoperative gastro-cutaneous fistula that did not resolve with conservative treatment. It was closed with only one session of Tissucol sealing. We consider that the endoscopic application of fibrin glue should become the first step in the conservative treatment of small esophageal perforations or postoperative esophageal pleural fistulae, especially in cases of high output fistulae. The success of this technique depends on the localization and selective catheterization of the fistula and on brushing the fistular opening. Total resolution of any distal stenosis is necessary to prevent reopening of the fistula.

3-[3-(Piperidin-1-yl)propyl]indoles as highly selective h5-HT(1D) receptor agonists

Several 5-HT(1D/1B) receptor agonists are now entering the marketplace as treatments for migraine. This paper describes the development of selective h5-HT(1D) receptor agonists as potential antimigraine agents which may produce fewer side effects. A series of 3-[3-(piperidin-1-yl)propyl]indoles has been synthesized which has led to the identification of 80 (L-772,405), a high-affinity h5-HT(1D) receptor full agonist having 170-fold selectivity for h5-HT(1D) receptors over h5-HT(1B) receptors. L-772,405 also shows very good selectivity over a range of other serotonin and nonserotonin receptors and has excellent bioavailability following subcutaneous administration in rats. It therefore constitutes a valuable tool to delineate the role of h5-HT(1D) receptors in migraine. Molecular modeling and physical properties have been utilized to postulate the binding conformation of these compounds in the receptor cavity.

[Treatment of inoperable malignant gastric stenosis with self-expanding prosthesis]

We report two patients with inoperable malignant stenosis of gastric antrum who were treated with endoscopic placement of a 22 mm Wallstent metallic prosthesis. In one patient, the endoscope was introduced simultaneously with the prosthesis. Different types of pincers were introduced through the endoscope's canal, which aided the movement and placement of the prosthesis. In the other patient, to broaden the stenosis a pediatric endoscope was introduced with a guide inside the canal, which was held straight externally and which facilitated the positioning of the prosthesis. There were no complications and the patients were discharged after 48 hours able to follow a normal oral diet. Both patients are still living, six and four months respectively after the procedure.

Parallel synthesis of 3-aryloxy-2-propanolamines and evaluation as dual affinity 5-HT(1A) and 5-HT re-uptake ligands

A solution phase synthesis for the preparation of 3-aryloxy-2-propanolamine libraries has been developed. This resulted in the identification of 5 as a ligand with dual affinity for 5-HT1A and serotonin reuptake receptors which shows excellent pharmacokinetic parameters.

Central benzodiazepine involvement in clonidine cardiovascular actions

It is well known that the GABAergic and noradrenergic systems play an important role in blood pressure and heart rate regulation. Benzodiazepines and beta-carbolines, respectively, increase or decrease the probability of chloride-channel opening induced by GABA. The aim of this study was to determine, in conscious rats, the interaction existing between the central alpha2-adrenoceptor stimulation induced by clonidine and the facilitation or impairment of benzodiazepine receptor activity through the administration of either diazepam, a benzodiazepine receptor agonist, or methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), an inverse benzodiazepine agonist. Clonidine (5-10 microg, intracerebroventricularly) reduced heart rate and increased mean blood pressure by activation of central alpha2-adrenoceptors. Diazepam (2 mg/kg, intravenously (i.v.)) induced an increase in heart rate, while DMCM (0.3 mg/kg, i.v.) elicited a bradycardic effect. The bradycardic effects induced by both clonidine and DMCM were antagonized by the prior administration of methylatropine (1.5 mg/kg, i.v.). DMCM (0.3 mg/kg, i.v.) prevented the clonidine effects on heart rate and mean blood pressure, while diazepam (2 mg/kg, i.v.) failed to modify these effects. Our results suggest that the bradycardic effects of clonidine are mediated by a vagal stimulation and are related to the activation of a GABAergic pathway.

2,7-diazabicyclo[3.3.0]octanes as novel h5-HT receptor agonists

The conformational restriction of a (benzylamino)methyl substituted pyrrolidine to form 2,7-diazabicyclo[3.3.0]octanes has led to a series of compounds with high affinity at the h5-HT1D receptor as well as dramatically increased concentrations in the hepatic portal vein following oral administration.

Fluorination of 3-(3-(piperidin-1-yl)propyl)indoles and 3-(3-(piperazin-1-yl)propyl)indoles gives selective human 5-HT1D receptor ligands with improved pharmacokinetic profiles

It has previously been reported that a 3-(3-(piperazin-1-yl)propyl)indole series of 5-HT1D receptor ligands have pharmacokinetic advantages over the corresponding 3-(3-(piperidin-1-yl)propyl)indole series and that the reduced pKa of the piperazines compared to the piperidines may be one possible explanation for these differences. To investigate this proposal we have developed versatile synthetic strategies for the incorporation of fluorine into these ligands, producing novel series of 4-fluoropiperidines, 3-fluoro-4-aminopiperidines, and both piperazine and piperidine derivatives with one or two fluorines in the propyl linker. Ligands were identified which maintained high affinity and selectivity for the 5-HT1D receptor and showed agonist efficacy in vitro. The incorporation of fluorine was found to significantly reduce the pKa of the compounds, and this reduction of basicity was shown to have a dramatic, beneficial influence on oral absorption, although the effect on oral bioavailability could not always be accurately predicted.

5-(Piperidin-2-yl)- and 5-(homopiperidin-2-yl)-1,4-benzodiazepines: high-affinity, basic ligands for the cholecystokinin-B receptor

The design, synthesis, and biological activity of a series of high-affinity, basic ligands for the cholecystokinin-B receptor are described. The compounds, which incorporate a piperidin-2-yl or a homopiperidin-2-yl group attached to C5 of a benzodiazepine core structure, are substantially more basic (e.g., 9d, pKa = 9.48) than previously reported antagonists based on 5-amino-1,4-benzodiazepines (e.g., 5, pKa = 7.1) and have improved aqueous solubility. In view of their basicity, it would be tempting to speculate that the present series of compounds might be binding to the CCK-B receptor in their protonated form. Compounds such as 9d, e and 10d showed high affinity for this receptor (IC50 < 2.5 nM) and very good selectivity over CCK-A (CCK-A/CCK-B > 2000), even as the racemates. Additionally, a significantly improved in vivo half-life was observed for a selection of compounds compared to the clinical candidate L-365, -260 (1).

Controlled modification of acidity in cholecystokinin B receptor antagonists: N-(1,4-benzodiazepin-3-yl)-N'-[3-(tetrazol-5-ylamino) phenyl]ureas

The design, synthesis, and biological activity of a novel series of CCK-B receptor antagonists (1) which incorporate a tetrazol-5-ylamino functionality attached to the phenyl ring of the arylurea moiety of L-365,260 are described. In these compounds, the acidity of the tetrazole was gradually modified by utilization of simple conformational constraints, and X-ray crystallographic data were obtained to support the conformational depenence of the pK(a) of the aminotetrazoles. Compounds to emerge from the present work such as 1f and 2c,d are among the highest affinity and, in the case of 1f, most selective (CCK-A/CCK-B, 37 000) antagonists so far reported for this receptor. The C(5)-cyclohexyl compound 2c (L-736,380) dose-dependently inhibited gastric acid secretion in anesthetized rats (ID(50), 0.064 mg/kg) and ex vivo binding of [(125)I]CCK-8S in BKTO mice brain membranes (ED(50), 1.7 mg/kg) and is one of the most potent acidic CCK-B receptor antagonists yet described.

Quantitative modifications induced by angiotensin II on rat bile secretion

Angiotensin II (ANG II) effects on bile secretion were studied in the rat. ANG II (0.1 microgram/kg) was injected into the jugular vein every 30 min and bile samples of 30 min were collected for 120 min. Blood arterial and portal venous pressures were simultaneously recorded before and after the administration of ANG II. Results showed that ANG II decreased bile flow and the excretion of sodium, potassium, chloride and bile acids whereas it increased pH, bile osmolality and the excretion rate of bicarbonate and calcium. ANG II also led to a rapid increase in mean arterial pressure as well as portal venous pressure which reverted to control values within 1 min. The present results suggest that ANG II may modulate bile flow and the excretion rate of the different biliary constituents. We have previously investigated atrial natriuretic factor effects on bile secretion and although the atrial factor antagonizes most of ANG II biological actions, unexpectedly, ANG II effects on bile secretion were not opposite to those of atrial natriuretic peptide. The modifications induced by ANG II on bile secretion may play an important role in pathophysiological conditions such as hypertensive states with increased ANG II circulating levels.

Synthesis and biological activity of 3-[2-(dimethylamino)ethyl]-5-[(1,1-dioxo-5-methyl-1,2,5-thiadiazolidin- 2-yl)-methyl]-1H-indole and analogues: agonists for the 5-HT1D receptor

A novel series of 5-(1,1-dioxo-1,2,5-thiadiazolidin-2-yl)tryptamines was designed, synthesized, and evaluated as 5-HT1D receptor agonists. Compounds such as 8d,f,k were identified which had comparable affinity, potency, and receptor selectivity to that of the antimigraine drug sumatriptan. Both 8d,k were found to be well absorbed in the rat with oral bioavailabilities of 66% and 62%, respectively. Additionally, 8d was found to be selective over other non-serotonergic receptors and exhibited relatively low central nervous system penetration.

Synthesis and serotonergic activity of 5-(oxadiazolyl)tryptamines: potent agonists for 5-HT1D receptors

The synthesis and 5-HT1D receptor activity of a novel series of 5-(oxadiazolyl)tryptamines is described. Modifications of the oxadiazole 3-substituent, length of the linking chain (n), and the amine substituents are explored and reveal a large binding pocket in the 5-HT1D receptor domain. Oxadiazole substituents such as benzyl are accommodated without loss of agonist potency or efficacy. The incorporation of polar functionality on a phenyl or benzyl spacer group results in a 10-fold increase in affinity and functional potency. Optimal 5-HT1D activity is observed when the heterocycle is conjugated with the indole and the benzyl sulfonamides 20t and 20u represent some of the most potent 5-HT1D agonists known. Replacement of O for S in the heterocycle leads to a further increase in potency. Deletion of oxadiazole N-2 does not reduce activity, suggesting the requirement for only one H-bond acceptor in this location. The selectivity of these compounds for 5-HT1D receptors over other serotonergic receptors is discussed. Sulfonamide 20t shows > or = 1000-fold selectivity for 5-HT1D over 5-HT2, 5-HT1C, and 5-HT3 receptors and 10-fold selectivity with respect to 5-HT1A receptors. The functional activity of this series of compounds is studied and demonstrates high 5-HT1D receptor potency and efficacy comparable to that of 5-HT.

Neovascular glaucoma after helium ion irradiation for uveal melanoma

Neovascular glaucoma developed in 22 of 169 uveal melanoma patients treated with helium ion irradiation. Most patients had large melanomas; no eyes containing small melanomas developed anterior segment neovascularization. The mean onset of glaucoma was 14.1 months (range, 7-31 months). The incidence of anterior segment neovascularization increased with radiation dosage; there was an approximately three-fold increase at 80 GyE versus 60 GyE of helium ion radiation (23% vs. 8.5%) (P less than 0.05). Neovascular glaucoma occurred more commonly in larger tumors; the incidence was not affected by tumor location, presence of subretinal fluid, nor rate of tumor regression. Fifty-three percent of patients had some response with intraocular pressures of 21 mmHg or less to a combination of antiglaucoma treatments.