Modulation of vitronectin receptor-mediated osteoclast adhesion by Arg-Gly-Asp peptide analogs: a structure-function analysis.

This study details the investigation of induction of retractile shape change in the osteoclast through inhibition of adhesion between osteoclasts and matrix with (1) peptide analogs bearing an Arg-Gly-Asp (RGD) sequence, (2) antibodies to the integrin alpha V beta 3 vitronectin receptor, and (3) the RGD-containing snake venom peptide echistatin. Osteoclast retraction on dentin has been demonstrated for GRGDSP peptide, in contrast to the inactivity of the analog containing the conservative RGE sequence modification. An osteoclast adhesion assay employing rat or chick bone cells and serum-coated glass coverslips as substrate was developed for routine evaluation of inhibition of adhesion. Antibodies F4 and F11 to the beta 3 chain of rat vitronectin receptor were effective at submicromolar concentrations in rat osteoclasts (IC50 0.29 and 0.05 microM, respectively), whereas MAb 23C6 to human/chick vitronectin receptor was somewhat less effective against chick osteoclasts (IC50 1.6 microM). A rank order of RGD analog activity (mean IC50, microM) in the serum-coated glass adhesion assay was derived for the linear peptides GRGDSP (201 microM), GRGDTP (180 microM), Ac-RGDS-NH2 (84 microM), Ac-RGDV-NH2 (68 microM), RGDV (43 microM), GRGDS (38 microM), and RGDS (26 microM). The two most potent short peptides were the cyclic analog SK&F 106760 Ac-S,S-cyclo-(Cys-(N alpha Me)Arg-Gly-Asp-Pen)-NH2 (IC50 7.0 microM), and the Telios peptide H-Gly-S,S-cyclo-(Pen-Gly-Arg-Gly-Asp-Ser-Pro-Cys)-Ala-OH (IC50 6.6 microM). The snake venom peptide echistatin was the most potent substance evaluated in the serum-coated glass assay (IC50 0.78 nM) employing either rat or chick osteoclasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Potent vasopressin antagonists lacking the proline residue at position 7.

As part of a program to design potent antidiuretic vasopressin antagonists and to define the minimum effective pharmacophore requirements for vasopressin (VP) antagonist activity, we studied the importance of the C-terminal tripeptide of a previously reported peptide antagonist of arginine-vasopressin (AVP,1). The proline residue at position 7 in AVP is proposed to impart a conformational constraint to the peptide backbone that is essential for V2-receptor agonist activity. Since the structure-activity relationships for VP agonists and antagonists are different, we investigated the effect of proline on antagonist activity, by synthesizing analogue 3 lacking this residue. This analogue was found to retain a high degree of antidiuretic antagonist activity. Since deletion of the Gly residue at position 9 of the antagonist did not adversely affect VP antagonist potency, several vasopressin antagonist analogues (4-7 and 9) that lacked both the Pro and Gly residues were also studied. These, too, were found to block vasopressin V2-receptor activity. Our results indicate that neither the proline nor glycine residues are essential for antagonism of the V2 receptor.

Imidodisulfamides. 2. Substituted 1,2,3,4-tetrahydroisoquinolinylsulfonic imides as antagonists of slow-reacting substance of anaphylaxis.

As part of a study of the influence of structural modifications of N',N'-bis(aralkyl)imidodisulfamides on their ability to selectively antagonize SRS-A activity, a few conformationally constrained structures were examined. Among these derivatives having a conformationally restricted alkylene side chain, substituted 1,2,3,4-tetrahydroisoquinolinylsulfonic imides produced optimum SRS-A antagonist activity and selectivity. These compounds were tested for antagonism of partially purified SRS-A induced contractions of isolated guinea pig ileum. In this series of tetrahydroisoquinolines, the effect of aromatic ring substitution, as well as substitution and variation of the size of the heterocyclic ring on SRS-A antagonist activity and selectivity, was studied.

Imidodisulfamides. 1. A novel class of antagonists of slow-reacting substance of anaphylaxis.

A series of N',N"-bis(aryl)- and N',N"-(aralkyl)imidodisulfamides was prepared and evaluated as antagonists of slow-reacting substance of anaphylaxis (SRS-A) induced contractions of isolated guinea pig ileum. Some of these compounds, notably N',N"-bis(4-phenylbutyl)-, N',N"-bis[2-(4-chlorophenyl)ethyl]-, and N',N"-bis[2-(4-bromophenyl)ethyl]imidodisulfamides (16, 22, and 26), were moderately potent and selective antagonists of SRS-A. The influence of lipophilic (pi) and electronic (sigma) factors on SRS-A antagonist activity appears to be of considerable importance to the derivation of potent and selective SRS-A antagonists.

Investigation of conformational specificity at GPIIb/IIIa: evaluation of conformationally constrained RGD peptides.

RGD-containing proteins and peptides are known to bind to the platelet GPIIb/IIIa receptor and inhibit platelet aggregation. That a conformational component to the specificity exists is suggested by significantly lower activity of linear RGD analogs relative to closely related cyclic peptides and small proteins containing the RGD sequence. Recently, conformations for a suite of RGD containing cyclic peptides have been defined by NMR-based methods and, for one molecule, by X-ray diffraction. We report here the NMR-based conformational analysis of an additional cyclic peptide, cyclo(Pro-Arg-Gly-Asp-D-Pro-Gly), and compare the conformational variations in the suite of peptides and related analogs. Biological activity data for these peptides shows a preference of the platelet GPIIb/IIIa receptor for one conformation of the RGD sequence, but suggests its ability to bind a second, distinct conformation.

Potent vasopressin antagonists modified at the carboxy-terminal tripeptide tail.

In a continuing effort to design more potent renal vasopressin (V2 receptor) antagonists, we have focused our attention on the carboxy-terminal tripeptide tail (Pro-Arg-Gly-NH2), a fragment common to both agonists and antagonists. Vasopressin antagonist analogues having a dibasic dipeptide tail, e.g., Arg-Arg-NH2 or Arg-Lys-NH2, attached directly to the cyclic hexapeptide ring are potent V2-receptor antagonists. Similar modification of a representative agonist drastically reduces its potency. We report the synthesis and pharmacological properties of a series of potent V2-receptor antagonists 3-9 where a combination of D or L dibasic dipeptide has been utilized to replace the common tripeptide fragment. Our results suggest a difference in the way agonists and antagonists bind to vasopressin receptor and further support the difference in the structure-activity relationships of agonists and antagonists. These results provide potentially useful insights for the design of novel V2-receptor antagonists.

Orally active and potent inhibitors of gamma-aminobutyric acid uptake.

3-Pyrrolidineacetic acid (1a), certain piperidinecarboxylic acids--i.e., 3-piperidinecarboxylic acid (2a), 1,2,5,6-tetrahydro-3-pyridinecarboxylic acid (3a), and cis-4-hydroxy-3-piperidinecarboxylic acid (4a)--cis-3-aminocyclohexanecarboxylic acid (5a, cis-3-ACHC), and gamma-aminobutyric acid (6a, GABA) itself are among the most potent inhibitors of [3H]GABA uptake by neurons and glia in vitro. These hydrophilic amino acids, however, do not readily enter the central nervous system in pharmacologically significant amounts following peripheral administration. We now report that N-(4,4-diphenyl-3-butenyl)-3-piperidinecarboxylic acid (2b) is a specific GABA-uptake inhibitor that is more potent, more lipophilic and, in limited testing, as selective as 2a. Similar results were obtained with the N-(4,4-diphenyl-3-butenyl) derivatives of 1a, 3a, and 4a. By contrast, N-(4,4-diphenyl-3-butenyl) derivatives of 5a and 6a were not more potent than the parent amino acids and appear to inhibit GABA uptake, at least in part, by a nonselective mechanism of action. The N-(4,4-diphenyl-3-butenyl)amino acids 1b-4b exhibit anticonvulsant activity in rodents following oral or intraperitoneal administration [Yunger, L.M.; et al. J. Pharmacol. Exp. Ther. 1984, 228, 109].

Conformationally constrained peptides and semipeptides derived from RGD as potent inhibitors of the platelet fibrinogen receptor and platelet aggregation.

Structure-activity studies have been pursued on cyclo-S,S-[Ac-Cys-(N alpha-Me)Arg-Gly-Asp-Pen]-NH2, 2 (SK&F 106760), a potent inhibitor of platelet aggregation, in an effort to improve potency and affinity for the GPIIb/IIIa receptor. Modifications on the N- and C-termini of 2 produced a series of peptides which indicate that the C-terminal carboxylate group may be a secondary receptor-binding element. Further modification by replacing the disulfide tether N alpha-acetylcysteine/penicillamineamide with the novel, inexpensive, achiral, constrained, and more lipophilic tether 2-mercaptobenzoyl/2-mercaptoaniline (Mba/Man) afforded the semipeptide cyclo-S,S-[Mba-(N alpha-Me)Arg-Gly-Asp-Man], 18 (SK&F 107260), which exhibited significant enhancement in both affinity and potency. To further investigate the effect of the phenyl ring at the C-terminus, peptides bearing the novel (2R,3S)- and (2R,3R)-beta-phenylcysteines were synthesized, which culminated in the cyclo-S,S-[Ac-Cys-(N alpha-Me)Arg-Gly-Asp-(2R,3S)-beta-phenylCys]-OH peptide, 22, which displayed substantial affinity and potency. We describe, herein, the development of both 18 and 22 and the additional structural modifications within the constrained cyclic disulfide ring to probe the stereochemical and steric requirements for receptor interaction.

The in vitro pharmacological profile of SK&F 106760, a novel GPIIB/IIIA antagonist.

The properties of SK&F 106760 [N alpha-acetyl-cyclo(S,S)-cysteinyl-N alpha-methyl-arginyl-glycyl-aspartyl-penicillamine-amide] as a GPIIb/IIIa antagonist have been studied in vitro and compared with those of the parent molecule, Ac-RGDS-NH2. Ac-RGDS-NH2 inhibited biotinylated fibrinogen binding to purified human GPIIb/IIIa immobilized on plastic microtitre plates with a Ki of 530 +/- 73 nM. In canine platelet rich plasma Ac-RGDS-NH2 produced a concentration related inhibition of adenosine diphosphate-induced platelet aggregation following preincubation for 3 min with an IC50 of 91 +/- 1 microM. However, incubation in platelet rich plasma for 3 hr abolished the activity of Ac-RGDS-NH2. SK&F 106760 inhibited biotinylated fibrinogen binding to purified human GPIIb/IIIa immobilized on plastic microtitre plates with a Ki of 477 +/- 57 pM. SK&F 106760 inhibited adenosine diphosphate-induced platelet aggregation in human platelet rich plasma with an IC50 of 230 +/- 60 nM but did not inhibit the von Willebrand Factor receptor (GPIb/IX)-mediated platelet agglutination produced by ristocetin. In canine platelet rich plasma SK&F 106760 inhibited aggregation produced by adenosine diphosphate, collagen and epinephrine/U-46619 with IC50 values of 355 +/- 35, 260 +/- 20, and 490 +/- 90 nM, respectively and in gel filtered platelets inhibited thrombin-mediated aggregation with an IC50 of 188 +/- 10 nM. Preincubation of SK&F 106760 in platelet rich plasma for three hours had no significant effect on its ability to inhibit adenosine diphosphate-induced platelet aggregation. SK&F 106760 produced insurmountable inhibition of adenosine diphosphate-induced platelet aggregation in the presence of constant fibrinogen concentrations, but produced competitive inhibition of the concentration-response curve to fibrinogen in adenosine diphosphate-activated platelets with a Kb of 8.0 +/- 1.0 nM. Thus, SK&F 106760 is a potent, stable competitive GPIIb/IIIa antagonist with no detectable activity at the von Willebrand Factor receptor (GPIb/IX).

Treatment of hyperthyroidism in Down syndrome: case report and review of the literature.

Thyroid disorders are common in individuals with Down syndrome (DS). Hyperthyroidism occurs much less frequently than hypothyroidism in this population, but is likely to be underestimated. We report a case of an institutionalized adult male with DS and hyperthyroidism. He was treated with radioactive iodine and, when reviewed 11 weeks later, was found to be markedly hypothyroid. We also review the literature on the three treatment options for hyperthyroidism in DS: surgery, medical treatment, and radiotherapy. We concluded that the place of radioiodine in the treatment of hyperthyroid patients with DS is yet to be defined.

Cryptosporidiosis among children attending the Maternity and Paediatrics Teaching Hospital, Wad Medani, Central Region, Sudan.

Modified Ziehl Neelson staining technique was used to identify Cryptosporidium species oocysts in stool specimens. Faecal samples from 166 children with diarrhoea and from a control of 95 children, were submitted for examination. 13 children from among those with diarrhoea and none from the control group were found to have Cryptosporidium species oocysts. The majority of these 13 positive children presented with abdominal pain, nausea, low grade fever and anorexia.

Regioselective alkylation at the N4 position of a 3-oxo-1,4-benzodiazepine on solid support.

An efficient solid phase regioselective alkylation at the N4 position of a 3-oxo-1,4-benzodiazepine template exemplified by 4-H-2,3,4,5-tetrahydro-7-iodo-3-oxo-1H-1,4-benzodiazepine-2-acetate-polymer ester is described. Further chemical elaboration at position 7, utilizing a modified Heck reaction, allows the incorporation of amides from primary or secondary amines. The two diversity points at positions 4 and 7 were utilized to synthesize a 28-membered, combinatorial array on Sasrin resin in moderate yields and > 80% purity. Having validated the chemistry on solid support, a combine and split approach to prepare a bead-bound combinatorial library is achievable utilizing similar experimental practices and procedures as in the array synthesis.

Design of a potent and orally active nonpeptide platelet fibrinogen receptor (GPIIb/IIIa) antagonist.

The direct design of the potent nonpeptide platelet fibrinogen receptor (GPIIb/IIIa) antagonist, 8-[[[4- (aminoiminomethyl)phenyl]amino]carbonyl]-2,3,4,5-tetrahydro-3-oxo- 4- (2-phenylethyl)-1H-1,4-benzodiazepine-2-acetic acid, (3) (SB 207448), based on the structure and conformation of the potent and highly constrained cyclic peptide antagonist SK&F 107260 (2), has been reported [Ku et al., J. Am. Chem. Soc. 1993, 115, 8861]. While 3 displayed in vivo activity in the conscious dog following intravenous administration, it was not active following intraduodenal administration; activity was measured with an ex vivo platelet aggregation assay. The secondary amide in 3 was N-methylated in the expectation of increased absorption and bioavailability. The resulting tertiary amide, 4 (SB 208651), also showed high binding affinity for human GPIIb/IIIa and potent antiaggregatory activity in human platelet-rich plasma. Most importantly, 4 was active in vivo following intravenous and intraduodenal administration. Comparison of the iv and id inhibition curves suggests an apparent bioavailability of approximately 10%. Thus, 4 represents the first orally active compound in this series of potent, nonpeptide fibrinogen receptor antagonists.

Binding of [3H]-SK&F 107260 and [3H]-SB 214857 to purified integrin alphaIIbbeta3: evidence for a common binding site for cyclic arginyl-glycinyl-aspartic acid peptides and nonpeptides.

The aggregation of activated platelets is mediated by the binding of fibrinogen to its cell surface receptor, the integrin alphaIIbbeta3. The recognition of fibrinogen by alphaIIbbeta3 depends, in part, on the tripeptide sequence Arg-Gly-Asp (RGD) in the adhesive protein. The interactions of a cyclic RGD-containing pentapeptide, [3H]-SK&F-107260, and a 1,4-benzodiazepine-based nonpeptide [3H]-SB-214857, with purified alphaIIbbeta3 have been investigated. Both compounds potently inhibit platelet aggregation at submicromolar concentrations. Binding of both [3H]-SK&F-107260 (Kd = 1.19 nM) and [3H]-SB-214857 (Kd = 1.85 nM) to alphaIIbbeta3 is of high affinity and fully reversible. The binding is monophasic, indicating a single class of noncooperative binding sites. The two radioligands exhibited similar values in binding to alphaIIbbeta3 purified on an RGD-affinity column (Bmax = 0.2 mol/mol alphaIIbbeta3) or to alphaIIbbeta3 purified over a lentil lectin column (Bmax = 0.03 mol/mol alphaIIbbeta3), suggesting that SK&F-107260 and SB-214857 interact with the same population of receptors. Binding of [3H]-SK&F-107260 and [3H]-SB-214857 to alphaIIbbeta3 require divalent cations, Mg++, Ca++ and Mn++ are able to support binding, with Mn++ being the most effective. Thirteen alphaIIbbeta3 antagonists, including four linear and three cyclic RGD peptides, five peptidomimetics, the fibrinogen gamma-chain dodecapeptide (HHLGGAKQAGDV) and the snake venom protein, echistatin, complete for [3H]-SK&F-107260 or [3H]-SB-214857 binding to alphaIIbbeta3. The affinity constants (Ki) of these compounds, determined by the two radioligand binding assays, are similar. Furthermore, these compounds exhibit the same rank order of potency in inhibiting biotinylated-fibrinogen binding to alphaIIbbeta3. Scatchard plot analyses of the [3H]-SK&F-107260 binding isotherms in the presence of unlabeled SB-214857 and gamma-chain dodecapeptide reveal competitive-type antagonism, indicating that SB-214857, gamma-chain dodecapeptide and SK&F-107260 interact with mutually exclusive binding sites on alphaIIbbeta3.

Benzimidazole derivatives as arginine mimetics in 1,4-benzodiazepine nonpeptide vitronectin receptor (alpha v beta 3) antagonists.

In a 3-oxo-1,4-benzodiazepine-2-acetic acid series of vitronectin receptor (alpha v beta 3) antagonists containing a benzimidazole as a novel arginine mimetic, we examined the effects of benzimidazole modifications and amide substitutions on both activity and pharmacokinetics.

Discovery of an imidazopyridine-containing 1,4-benzodiazepine nonpeptide vitronectin receptor (alpha v beta 3) antagonist with efficacy in a restenosis model.

In the 3-oxo-1,4-benzodiazepine-2-acetic acid series of vitronectin receptor (alpha v beta 3) antagonists, a compound containing an imidazopyridine arginine mimetic was discovered which had sufficient potency and i.v. pharmacokinetics for demonstration of efficacy in a rat restenosis model.