Raymond S. L. Chang

Effects of Subtype-Selective and Balanced Angiotensin II Receptor Antagonists in a Porcine Coronary Artery Model of Vascular Restenosis

BACKGROUND Numerous studies have demonstrated the ability of angiotensin II (Ang II) receptor antagonists and angiotensin-converting enzyme (ACE) inhibitors to inhibit intimal hyperplasia after balloon dilation of noncoronary arteries in small-animal models, suggesting an important role for Ang II in the response to injury. Although ACE inhibitors have not been similarly effective in nonhuman coronary models or in human restenosis trials, questions remain regarding the efficacy ACE inhibitors against tissue ACE and the contributions of ACE-independent pathways of Ang II generation. Unlike ACE inhibitors, Ang II receptor antagonists have the potential to inhibit responses to Ang II independent of its biosynthetic origin. METHODS AND RESULTS In separate studies, three Ang II receptor antagonists, including AT1 selective (L-158,809), balanced AT1/AT2 (L-163,082), and AT2 selective (L-164,282) agents, were evaluated for their ability to inhibit vascular intimal thickening in a porcine coronary artery model of vascular injury. Preliminary studies in a rat carotid artery model revealed that constant infusion of L-158,809 (0.3 or 1.0 mg X kg-1 X d-1) reduced the neointimal cross-sectional area by up to 37% measured 14 days after balloon dilatation. In the porcine studies, animals were treated with vehicle or test compound beginning 2 days before and extending 28 days after experimental angioplasty. Left anterior descending, left circumflex, and/or right coronary arteries were injured by inflation of commercially available angioplasty balloons with placement of coiled metallic stents. Infusion of L-158,809 (1 mg X kg-1 X d-1), L-163,082 (1 mg X kg-1 X d-1), or L-164,282 (1.5 mg X kg-1 X d-1) in the study animals yielded plasma drug levels sufficient either to chronically block or, for L-164,282, to spare pressor responses to exogenous Ang II. Neither L-158,809, L-163,082, nor L-164,282 had statistically significant effects (P=.12, P=.75, and P=.48, respectively, compared with vehicle-treated controls) on neointimal thickness (normalized for degree of injury) measured by morphometric analysis at day 28 after angioplasty. CONCLUSIONS These findings indicate that chronic blockade of Ang II receptors by either site-selective or balanced AT1/AT2 antagonists is insufficient to inhibit intimal hyperplasia after experimental coronary vascular injury in the pig. The results further suggest that, unlike in the rat carotid artery, Ang II is not a major mediator of intimal thickening in the pig coronary artery.

Design and Synthesis of Novel α1a Adrenoceptor-Selective Dihydropyridine Antagonists for the Treatment of Benign Prostatic Hyperplasia

We report the synthesis and evaluation of novel α1a adrenoceptor subtype-selective antagonists. Systematic modification of the lipophilic 4,4-diphenylpiperidinyl moiety of the dihydropyridine derivatives 1 and 2 provided several highly selective and potent α1a antagonists. From this series, we identified the 4-(methoxycarbonyl)-4-phenylpiperidine analogue SNAP 5540 (−) [(−)-63] for further characterization. When examined in an isolated human prostate tissue assay, this compound was found to have a Ki of 2.8 nM, in agreement with the cloned human receptor binding data (Ki = 2.42 nM). Further evaluation of the compound in isolated dog prostate tissue showed a Ki of 3.6 nM and confirmed it to be a potent antagonist (Kb = 1.6 nM). In vivo, this compound effectively blocked the phenylephrine-stimulated increase in intraurethral pressure (IUP) in mongrel dogs, at doses which did not significantly affect the arterial pressure (diastolic blood pressure, DBP), with a DBP Kb/IUP Kb ratio of 16. In addition, (−)-63 ...

On the location of the sulfhydryl group in bovine plasma albumin

A series of spin labels has been empolyed to explore the environment of the sulfhydryl group in bovine plasma albumin. The spin labels consist of the nitroxide-free radical and a maleimide (or iodoacetamide)-attaching group separated by varying chain lenghths. Both sets of spin labels preferentially bind to the sulfhydryl group under appropriate conditions. From the change in the electron spin resonance spectra of these nitroxides as a function of chain length, we conclude that the sulfhydryl group is located in a crevice approx. 9.5 A in depth.

Molecular cloning and pharmacological characterization of the canine B1 and B2 bradykinin receptors.

Abstract The dog is a valuable animal model in the study of the physiological role of both the B1 and B2 bradykinin receptors. To more thoroughly characterize the pharmacological properties of the canine kinin receptors we isolated the cDNA sequence encoding the B1 and B2 bradykinin receptor subtypes and overexpressed them in Chinese hamster ovary (CHO) cells. The cDNA sequence of the canine B1 bradykinin receptor encodes a protein comprised of 350 amino acids that is 76% identical to the human B1 bradykinin receptor. The cDNA sequence of the canine B2 bradykinin receptor encodes a protein of 392 amino acids that is 81% identical to the human B2 bradykinin receptor. The amino acid sequence of the canine B1 and B2 receptors are 35% identical. Pharmacological studies of the cloned receptors revealed that the agonist affinity of the dog B1 receptor is similar to the rodent B1 receptors, and differs from the human form in that there is no preference for the presence of the Nterminal Lys residue of [desArg10]Lysbradykinin. Significantly, the B1 receptor antagonist [desArg9,Leu8]BK behaves as partial agonist on the cloned dog B1 receptor. The dog B2 receptor exhibits the classical pharmacological properties of this receptor subtype.

Design and Synthesis of Novel α1a Adrenoceptor-Selective Antagonists. 3. Approaches To Eliminate Opioid Agonist Metabolites by Using Substituted Phenylpiperazine Side Chains

Dihydropyrimidinones, such as 1, represent a novel class of alpha(1a) adrenoceptor antagonists with potential for the treatment of benign prostatic hyperplasia (BPH) (see part 1 of this series). Analysis of the metabolites of 1 revealed that 4-methoxycarbonyl-4-phenylpiperidine is formed as the major metabolite and is an agonist at the mu-opioid receptor. To circumvent any potential liability resulting from the metabolite, we decided to identify alternate templates devoid of agonist activity at the mu-opioid receptor to replace the 4-methoxycarbonyl-4-phenylpiperidine moiety. The present study describes the synthesis and SAR of dihydropyrimidinones linked to substituted 4-phenylpiperazine containing side chains. Compound (+)-38 was identified as a lead compound with a binding and functional profile comparable to that of 1. The putative metabolite 2-carboxamidophenylpiperazine has negligible affinity for the mu-opioid receptor.

SOLVENT INFLUENCES ON THE SINGLET QUENCHING OF CHLOROPHYLL a BY 2, 5‐DIMETHYL‐p‐BENZOQUINONE

Abstract— The quenching of chlorophyll a excited singlet states by 2.5‐dimethyl‐p‐benzoquinone has been investigated in solvents of varying viscosity and polarity. The observed singlet lifetimes showed little variation in several hydrocarbon solvents. Stern‐Volmer constant K depends on the viscosity of the solvent, although cyclic and straight‐chain hydrocarbons behave somewhat differently. The decrease of the K values with increase of viscosity suggests that the quenching mechanism is at least partly dynamic, although there is evidence for static quenching as well. The influence of solvent polarity on the K values was found to be insignificant, which is consistent with a very short‐lived ion pair intermediate formed by electron‐transfer quenching.

2-Aminobenzophenones as a novel class of bradykinin B1 receptor antagonists.

Selective bradykinin (BK) B 1 receptor antagonists could be novel therapeutic agents for the treatment of pain and inflammation. Elucidation of the structure activity relationships of the structurally novel HTS lead compound 1 provided potent hBK B 1 receptor antagonists with excellent receptor occupancy in the CNS of hBK B 1 transgenic rats.

Linear dichroism and fluorescence polarization of diphenyl polyenes in stretched polyethylene films

Abstract A study of the linear diehroism and fluorescence polarization of diphenylpolyenes (C 6 H 5 —(CH=CH) n —C 6 H 5 ) with n = 1,2,3,4,6,8 in stretched polyethylene films shows that the polyenes orient in the anisotropic matrix with their transition dipole (emission and absorption, π → π * ) aligned with the direction of stretch. The maximum dichroic ratio is observed for 1,6-diphenyl-1,3,5-hexatriene (DPH), with n = 3, whereas the values are substantially lower for n n > 3. The high orientation of DPH and poor alignment of the higher polyenes may be accounted for in terms of the growing flexibility of the polyene chains with increasing chain length. The results justify the use of DPH as a convenient fluorescence probe for biological and synthetic membranes.

The environment of the sulfhydryl group in human plasma albumin as determined by spin labeling

Abstract A series of spin labels, varying in chain length between the maleimide attaching group and the nitroxide free radical, has been used to investigate the environment of the sulfhydryl group in human plasma albumin. From the electron spin resonance spectra, the degree of freedom of the nitroxide was determined and the location of the sulfhydryl was assessed. The effect of bound fatty acids on the sulfhydryl environment was also determined. The environment was found to be analogous to that in the bovine protein, that is, a crevice approximately 9.5 A deep and not affected in the native state by fatty acids.

Protodediazoniation of Aryldiazonium Fluoroborates by Dimethylformamide [1]

Abstract The protodediazoniation of aryldiazonium fluoroborates can be effected by warm dimethylformamide (DMF). The conversion of 4-nitrobenzenediazonium fluoroborate to nitrobenzene was studied in detail. Products derived from trapping experiments were consistent with a homolytic process. Studies with deuterated DMF established that H atom abstraction occurred from both sites in DMF with a formyl:methyl preference of 3.5:1.0. This mechanism was consistent with bond energies and kinetic isotope effects calculated for the DMF radical cation.