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A M Doherty

Publications and source records attributed to A M Doherty.

At least 55 records · Page 3Linked to original sources
PubMed1997

Design of a potent combined pseudopeptide endothelin-A/endothelin-B receptor antagonist, Ac-DBhg16-Leu-Asp-Ile-[NMe]Ile-Trp21 (PD 156252): examination of its pharmacokinetic and spectral properties.

The endothelins (ETs) are a family of bicyclic 21-amino acid peptides that are potent and prolonged vasoconstrictors. It has been shown that highly potent combined ETA/ETB receptor antagonists can be developed from the C-terminal hexapeptide of ET (His16-Leu17-Asp18-Ile19-Ile20-Trp21), such as Ac-(D)Dip16-Leu-Asp-Ile-Ile-Trp21 (PD 142893) and Ac-DBhg16-Leu-Asp-Ile-Ile-Trp21 (PD 145065). However, these compounds are relatively unstable to enzymatic proteolysis as determined in an in vitro rat intestinal perfusate assay. This instability is thought to be due to carboxypeptidase activity. In fact, incubation of PD 145065 with carboxypeptidase inhibitors greatly increased its half-life in rat intestinal perfusate. By performing a reduced amide bond and N-methyl amino acid scan, it was discovered that N-methylation of Ile-20 resulted in a compound (Ac-DBhg16-Leu-Asp-Ile-[NMe]Ile-Trp21, PD 156252) that retained full receptor affinity at both endothelin receptor subtypes along with enhanced proteolytic stability and cellular permeability. Interestingly, N-methylation of this bond allows the cis configuration to be readily accessible which greatly alters the preferred structure of the entire molecule and may be responsible for the observed enhanced metabolic stability.

Amino Acid Sequence↗
PubMed1997

Structure-activity relationships in a series of orally active gamma-hydroxy butenolide endothelin antagonists.

The design of potent and selective non-peptide antagonists of endothelin-1 (ET-1) and its related isopeptides are important tools defining the role of ET in human diseases. In this report we will describe the detailed structure-activity relationship (SAR) studies that led to the discovery of a potent series of butenolide ETA selective antagonists. Starting from a micromolar screening hit, PD012527, use of Topliss decision tree analysis led to the discovery of the nanomolar ET(A) selective antagonist PD155080. Further structural modifications around the butenolide ring led directly to the subnanomolar ETA selective antagonist PD156707, IC50's = 0.3 (ET(A)) and 780 nM (ET(B)). This series of compounds exhibited functional activity exemplified by PD156707. This derivative inhibited the ETA receptor mediated release of arachidonic acid from rabbit renal artery vascular smooth muscle cells with an IC50 = 1.1 nM and also inhibited the ET-1 induced contraction of rabbit femoral artery rings (ETA mediated) with a pA2 = 7.6. PD156707 also displayed in vivo functional activity inhibiting the hemodynamic responses due to exogenous administration of ET-1 in rats in a dose dependent fashion. Evidence for the pH dependence of the open and closed tautomerization forms of PD156707 was demonstrated by an NMR study. X-ray crystallographic analysis of the closed butenolide form of PD156707 shows the benzylic group located on the same side of the butenolide ring as the gamma-hydroxyl and the remaining two phenyl groups on the butenolide ring essentially orthogonal to the butenolide ring. Pharmacokinetic parameters for PD156707 in dogs are also presented.

Administration, Oral↗
PubMed1997

Structure-activity relationships of cysteine-lacking pentapeptide derivatives that inhibit ras farnesyltransferase.

Mutational activation of ras has been found in many types of human cancers, including a greater than 50% incidence in colon and about 90% in pancreatic carcinomas. The activity of both native and oncogenic ras proteins requires a series of post-translational processing steps. The first event in this process is the farnesylation of a cysteine residue located in the fourth position from the carboxyl terminus of the ras protein, catalyzed by the enzyme farnesyltransferase (FTase). Inhibitors of FTase are potential candidates for development as antitumor agents. Through a high-volume screening program, the pentapeptide derivative PD083176 (1), Cbz-His-Tyr(OBn)-Ser(OBn)-Trp-DAla-NH2, was identified as an inhibitor of rat brain FTase, with an IC50 of 20 nM. Structure-activity relationships were carried out to determine the importance of the side chain and chirality of each residue. This investigation led to a series of potent FTase inhibitors which lack a cysteine residue as found in the ras peptide substrate. The parent compound (1) inhibited the insulin-induced maturation of Xenopus oocytes (concentration: 5 pmol/oocyte), a process which is dependent on the activation of the ras pathway.

Alkyl and Aryl Transferases↗
PubMed1997

Evaluation of the effect of endothelin-1 and characterization of the selective endothelin a receptor antagonist PD155080 in the prostate.

PURPOSE: To evaluate the contractile effect of endothelin-1 (ET-1) on prostatic urethral pressure and to characterize the effect of the selective ETA receptor antagonist PD155080 on ET-1 mediated prostatic urethral pressure. MATERIALS AND METHODS: The effect of intravenous ET-1 administration on canine urethral pressure was determined in the presence and absence of PD155080. The affinity of PD155080 for endothelin-mediated contraction was determined using antagonist dissociation studies. Saturation and competition binding studies were performed using [125I] ET-1 in both human and canine prostate. RESULTS: ET-1 bolus injection elicited shallow and prolonged increases the prostatic urethral pressure. Pretreatment with PD155080 totally abolished the urethral contractile response to ET-1. Specific [125I] ET-1 binding was saturable and of high affinity. Two ET receptor subtypes (ETA receptor, ETB receptor) have been identified in human prostate. The ratio of ETA to ETB receptors was approximately 1.5:1 in both human and canine prostates. Isometric tension studies revealed that PD155080 shifted the ET-1 dose-response curves to the right and exhibited no effect on the ETB receptor selective agonist sarafotoxin dose-response curves. CONCLUSION: ET-1 mediates prostate smooth muscle tone and may play a role in the pathophysiology and treatment of benign prostatic hyperplasia (BPH).

Animals↗
PubMed1997

In vitro pharmacological characterization of PD 166285, a new nanomolar potent and broadly active protein tyrosine kinase inhibitor.

PD 166285, a novel protein tyrosine kinase inhibitor of a new structural class, the 6-aryl-pyrido[2,3-d]pyrimidines, was synthesized as the most potent and soluble analog of a series of small molecules originally identified by screening a compound library with assays that measured protein tyrosine kinase activity. PD 166285 was found to inhibit Src nonreceptor tyrosine kinase, fibroblast growth factor receptor-1, epidermal growth factor receptor and platelet-derived growth factor receptor beta subunit (PDGFR-beta), tyrosine kinases with half-maximal inhibitory potencies (IC50 values) of 8.4 +/- 2.3 nM (n = 6), 39.3 +/- 2.8 nM (n = 16), 87.5 +/- 13.7 nM (n = 6) and 98.3 +/- 7.9 nM (n = 16), respectively. PD 166285 also demonstrated inhibitory activity against mitogen-activated protein kinase (IC50 = 5 microM) and protein kinase C (IC50 = 22.7 microM). PD 166285 was further characterized as an ATP competitive inhibitor of Src nonreceptor tyrosine kinase, PDGFR-beta, fibroblast growth factor receptor-1 and epidermal growth factor receptor tyrosine kinases. In addition, PD 166285 inhibited PDGF- and EGF-stimulated receptor autophosphorylation in vascular smooth muscle cells (VSMCs) and A431 cells, respectively, and basic fibroblast growth factor-mediated tyrosine phosphorylation in Sf9 cells, with IC50 values of 6.5 nM, 1.6 microM and 97.3 nM, respectively, further establishing a tyrosine kinase mechanism of inhibition. The inhibition of PDGF receptor autophosphorylation in VSMCs by PD 166285 was long lasting and persisted for 4 days after a single 1-hr exposure followed by extensive washing. The PDGF-induced tyrosine phosphorylation of the 44- and 42-kDa mitogen-activated protein kinase isoforms was also blocked as a result of the inhibition of PDGF-stimulated receptor autophosphorylation by PD 166285 in VSMCs. The effects of PD 166285 were also demonstrated in functional assays of cell attachment, migration and proliferation, in which vascular cell adhesion to vitronectin, PDGF-directed chemotaxis and serum-stimulated cell growth were all potently inhibited with IC50 values of 80 yo 120 nM. Finally, PD 166285 uniquely demonstrated potent inhibition of phorbol ester-induced production of 92-kDa gelatinase A (MMP-9) in VSMC without affecting 72-kDa gelatinase B (MMP-2) as measured by gelatin zymography. These results highlight the biological characteristics of PD 166285 as a broadly active protein tyrosine kinase capable of potently inhibiting a number of kinase mediated cellular functions, including cell attachment, movement and replication. The potential therapeutic utility of this broadly acting inhibitor as an antiproliferative and antimigratory agent could extend to such diseases as cancer, atherosclerosis and restenosis, in which redundancies in protein kinase signaling pathways are known to exist.

Animals↗
PubMed1996

Role of ET(B) receptors in local clearance of endothelin-1 in rat heart: studies with the antagonists PD 155080 and BQ-788.

The effects of two endothelin (ET) receptor antagonists, PD 155080 (ET(A) selective) and BQ-788 (ET(B) selective), on cardiac function and ET-1 release were studied in isolated rat hearts. In normoxic hearts, infusion of PD 155080 (50 nM-5 microM) reduced coronary resistance, but had no effect on ET-1 release. Low concentrations of BQ-788 (2 and 20 nM) had no effect on coronary resistance; high concentrations (0.2 and 2 microM) increased it approximately 2-fold; all concentrations increased ET-1 release (up to 24-fold). Similar results were obtained in reperfused hearts. Although concentrations of ET-1 were higher in interstitial fluid than coronary effluent, levels never exceeded the low pg/ml range. These results indicate that (1) ET(A) receptors mediate coronary constriction, whereas ET(B) receptors bind and sequester ET-1, and (2) ET-1 displaced by ET(B) antagonist accesses ET(A) receptors resulting in coronary constriction.

Animals↗
PubMed1996

In vitro assessment of oral delivery for hexapeptide endothelin antagonists.

Endothelin (ET-1) is a 21-amino acid, vasoconstrictive peptide originally isolated from endothelial cells. It is one member of a class of potent, purportedly paracrine substances that act at receptors in multiple target organs. Antagonists to the receptor subtypes, ETA and ETB, have been designed around the hydrophobic carboxy-terminus of ET-1. The resulting hexapeptides possess low nanomolar receptor affinity, but face formidable challenges to oral delivery, given their peptidic nature. Hence, it was important to discriminate between analogs, as well as to optimize structural features combining binding potency with stability in intestinal fluids and permeability across biological membranes. PD 142893 (Ac-DDip16-Leu-Asp-Ile-Trp21) and PD 145065 (Ac-DBhg16-Leu-Asp-Ile-Ile-Trp21), as well as the N-methyl-isoleucine20 analogs were studies, where DDip = 3,3diphenylalanine and DBhg = 10,11-dihydro-5H-dibenzo[a,d]cycloheptene glycine. Analyses were conducted with specific HPLC methods. Permeabilities across CACO-2 cell monolayers ranged from 2.0x10(-4) to 6.3x10(-4)cm/min. The results suggested that these compounds can be absorbed in vivo, based on comparison of permeabilities with those obtained with reference compounds. Much greater differences were observed between the analogs when stability half-lives were compared after incubation in rat intestinal perfusate. The parent peptides, PD 142893 and PD 145065, were unstable, with half-lives less than 20 min. N-Methylation of Ile20 resulted in large increases in stability half-lives to greater 500 min. Enzyme inhibition studies demonstrated the involvement of carboxypeptidase A in production of the primary metabolite, the des-Trp derivative. Identification of the primary metabolite of the parent peptide was made by differential UV scanning at 214/280 nm and mass spectral analyses.

Animals↗
PubMed1996

Endothelin receptor antagonist increases cerebral perfusion and reduces ischaemic damage in feline focal cerebral ischaemia.

These investigations characterised the cerebrovascular effects of an endothelin ETA-receptor antagonist PD156707 in normal and ischaemic cat brain. A dose of PD156707 that inhibited the effects of exogenous endothelin-1 was established in nonischaemic cerebral resistance arterioles. Perivascular microapplication of the endothelin-receptor antagonist PD156707 (0.03-3 microM) had a minimal effect on nonischaemic pial resistance arterioles. The perivascular co-application of PD156707 and ET-1 (10 nM) effected a dose-dependent attenuation of the ET-1 vasoconstrictive response (IC50 = 0.1 microM). Intravenous administration of PD156707 (3 mumol/kg bolus + 5 mumol/kg/h infusion) attenuated the vasoconstriction elicited by perivascular ET-1 (10 nM) in normal pial arterioles (ET-1 vasoconstriction: -37 +/- 13% from preinjection baseline; after intravenous PD156707: 6 +/- 10% from preinjection baseline). In the focal ischaemia studies, cerebral perfusion was measured in the suprasylvian and ectosylvian gyri (by laser Doppler flowmetry). Occlusion of the middle cerebral artery reduced cerebral perfusion in the suprasylvian and ectosylvian gyri by approximately 50%. Intravenous administration of PD156707 (3 mumol/kg bolus + 5 mumol/kg/h infusion), initiated 30 min after middle cerebral artery occlusion, effected a progressive increase in cerebral perfusion up to preocclusion baseline levels, whereas cerebral perfusion in vehicle-treated animals did not vary from its postocclusion level. In these animals, the intravenous administration of PD156707 reduced the hemispheric volume of ischaemic damage by 45% (vehicle: 2,376 +/- 1,107 mm3; PD156707: 1,307 +/- 548 mm3; p < 0.05). Our investigations indicate that endothelin receptor antagonism may be a new therapeutic strategy for the amelioration of focal ischaemic damage.

Animals↗
PubMed1996

Novel drimane sesquiterpene esters from Aspergillus ustus var. pseudodeflectus with endothelin receptor binding activity.

A series of novel drimane sesquiterpene esters (1-6) was isolated from fermentations of Aspergillus ustus var. pseudodeflectus and their structures elucidated by spectroscopic methods including the HMQC, HMBC and INADEQUATE NMR experiments. The major component of the fermentation, 1, was (2'E,4'E,6'E)-6-(1'-carboxy-2',4',6'-trien)-9-hydroxydrim-7-ene-11 ,12-olide. Compounds 1, 2, 3 and 5 exhibited endothelin receptor binding inhibitory activity against rabbit endothelin-A and rat endothelin-B receptors with IC50 values in the range 20-150 microM. These compounds had similar levels of activity in assays for binding to human endothelin A and endothelin B receptors. The isolation of 9,11-dihydroxy-6-oxodrim-7-ene, 7, a probable biosynthetic precursor to the drimane esters is also reported.

Animals↗
PubMed1995

Design and synthesis of renin inhibitors: incorporation of transition-state isostere side chains that span from the S1 to the S3 binding pockets and examination of P3-modified renin inhibitors.

A series of renin inhibitors were designed to examine the topography of the contiguous binding pocket of renin that is normally occupied by the P1 and P3 side chains. Molecular modeling suggested that extending the P1 hydrophobic side chain into the adjacent hydrophobic S3 enzyme pocket was feasible. Novel transition state isosteres with modified P1-->P3 side chains were synthesized and provided enhanced binding affinity when incorporated into renin inhibitors in which the P3 Phe was substituted by Gly. In a complementary approach, the binding affinities of a variety of P3-P4-modified peptidomimetic renin inhibitors that lacked substantial hydrophobic side chains at these sites were measured.

Amides↗
PubMed1995

Pharmacological differences between rat and human endothelin B receptors.

Cloned rat and human endothelin-B receptors (ETBR) were utilized to determine if there are significant pharmacological differences between highly homologous ETBR from different species. Recombinant rat and human ETBR were expressed in CHO-K1 cells, and radioligand binding studies were carried out with [125I]-ET-3 to determine the affinities of various ET receptor agonists and antagonists for rat and human ETBR. These receptors had similar affinities for a number of ETBR agonists (ET-1, ET-3, S6C, BQ 3020) and antagonists (Ro 47-0203, PD 142893). However, several peptide (PD 147452, PD 151583, BQ 788) and non-peptide (PD 156707, SB 209670) antagonists had different affinities for rat and human ETBR, with differences in Ki values between species ranging from 4.1- to 53.4-fold. The ETBR-selective agonist IRL 1620 also had a 5.7-fold higher affinity for rat ETBR than human ETBR. Thus despite their high degree of homology, rat and human ETBR show significant pharmacological differences with respect to both antagonist and agonist binding.

Amino Acid Sequence↗
PubMed1995

The development of potent peptide agonists and antagonists for the endothelin receptors.

The endothelins (ETs), sarafotoxins (SRTXs), vasoactive intestinal contractor (VIC), and bibrotoxin are a family of potent vasoconstrictor peptides. All peptides in this family possess 21 amino acids arranged in a unique bicyclic motif formed between cystine bridges in the 1-15 and 3-11 positions. Since the discovery of endothelin-1 (ET-1) in 1988, significant effort has been focused on the understanding of its structure-activity relationships. The identification of endothelin receptor subtypes has led to the discovery/design of potent peptide agonists and antagonists, along with nonpeptide antagonists of endothelin with varying levels of potency and receptor subtype selectivity. In keeping with the theme of this journal, this review will focus only on the development of peptidic-based agonists and antagonists of endothelin in addition to their applications in understanding the physiological and/or pathophysiological role of endothelin and its isopeptides.

Amino Acid Sequence↗
PubMed1995

Structure-activity studies of phosphorylated peptide inhibitors of the association of phosphatidylinositol 3-kinase with PDGF-beta receptor.

Phosphorylated pentapeptides derived from Tyr751 of the PDGF-beta receptor (pTyr751-Val-Pro-Met-Leu, pTyr = phosphotyrosine) were prepared to examine their ability to inhibit the association of the C-terminal SH2 domain of the p85 subunit of phosphatidylinositol 3-kinase (PI 3-kinase) with the PDGF-beta receptor. Peptidic analogs were prepared to examine the importance of the amine and carboxy terminus and specific amino acids via alanine/D-amino acid scans and site specific modifications. Several of these peptides had submicromolar activity. In particular, it was shown that neutralization of the amine and carboxy terminus led to analogs with enhanced activity. In addition, it was determined that only minimal modifications were allowed for pTyr and Met, while the other positions were quite tolerant of modification.

Alanine↗
PubMed1995

Structure-activity relationships of a novel series of orally active nonpeptide ETA and ETA/B endothelin receptor-selective antagonists.

The development of nonpeptide, low molecular weight antagonists with high potency, oral activity, and selectivity is an important objective to adequately define the potential role of endothelin (ET) and its isopeptides in human diseases. This report describes the structure-activity relationships, ETA/ETB selectivity, and pharmacokinetics of the PD 155080 and PD 156707 series of orally active nonpeptide ET receptor-selective antagonists. Modification of the substituents around the butenolide ring has led to compounds with differing selectivity for human ETA and ETB receptors. Thus, compounds with increased lipophilicity at R2 show increased ETB affinity and a more balanced ETA/ETB profile. For example, the 4-O-n-pentyl analogue of PD 156707 is a potent competitive inhibitor of [125I]ET-1 and [125I]ET-3 binding to human cloned ETA and ETB receptors, with IC50s of 0.8 nM and 44 nM, respectively. Pharmacokinetic properties can also be significantly influenced by structural modifications at the R2 group. The pharmacokinetics of PD 155719, PD 155080, and PD 156707 were compared in male Wistar rats after a 15 mg/kg intravenous or oral gavage dose (three animals per dose). Plasma concentrations were determined by a specific HPLC assay. Oral bioavailability ranged from less than 5% for PD 155719 to 41% for PD 156707 and 87% for PD 155080.

Animals↗
PubMed1995

Potency of PD155080, an orally active ETA receptor antagonist, determined for human endothelin receptors.

We have determined, for the first time, the potency of a new ETA-selective endothelin (ET) antagonist, PD155080, for human endothelin receptors. In sections of human left ventricle (n = 3) and human kidney (n = 5) PD155080 competed for specific [125I]ET-1 binding with Kd values at the ETA receptor of 221.4 +/- 25 nM and 19.0 +/- 23 nM and at the ETB receptor of 86.5 +/- 9.0 microM and 17.7 +/- 1.4 microM. PD155080 therefore has up to 1,000-fold selectivity for the human ETA receptor. The ability of this compound to antagonize ET-1-mediated vasoconstriction was determined in human isolated coronary artery, saphenous vein, and left internal mammary artery. Increasing concentrations of PD155080 caused a progressive, parallel rightward shift of the ET-1 concentration-response curve without detrimental effect on the maximal response to ET-1. The pA2 values determined by Schild analysis were 6.87 in coronary artery (n = 5), 6.75 in saphenous vein (n = 7), and 7.25 in mammary artery (n = 6). Slopes of the Schild regression lines were not significantly different from one, indicating a competitive mode of action. In addition, PD155080 (1 microM) fully reversed the established contraction to ET-1 (30 nM) in saphenous vein. The potency of this compound is comparable to that reported for the ETA-selective peptide antagonist BQ123 [cyclo(D-Trp-L-Asp-L-Pro-D-Val-L-Leu)], which is effective in limiting tissue damage caused by ET-1 in animal models of pathologic vasospasm. PD155080 may therefore be a good candidate for clinical use in diseases, such as subarachnoid hemorrhage, in which the ET system is implicated.

Administration, Oral↗
PubMed1995

Therapeutic potential of endothelin receptor antagonists in experimental stroke.

This investigation demonstrates an increase in endothelin (ET)-mediated vascular tone in peri-ischemic areas after experimental focal cerebral ischemia (middle cerebral artery occlusion) in the cat. Adventitial application of the butenolide antagonist PD155080 (30 microM), after MCA occlusions resulted in marked increases in caliber of dilated (10.6 +/- 1.6% change from preinjection baseline) and constricted vessels (68.7 +/- 17.5% change from pre-injection baseline). Cerebral blood flow (measured by laser Doppler flowmetry) was reduced after MCA occlusion to 50% of preocclusion levels. Intravenous administration of PD156707 30 min after MCA occlusion restored cerebral blood flow to preocclusion baseline levels at 6 h. The volume of ischemic damage in the cerebral hemisphere after MCA occlusion was significantly reduced (by 45%) after intravenous administration of PD156707.

Animals↗