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Title: Muscarinic receptor subtype selectivity of novel heterocyclic QNB analogues

Abstract

In an effort at synthesizing centrally-active subtype-selective antimuscarinic agents, the authors derivatized QNB (quinuclidinyl benzilate), a potent muscarinic antagonist, by replacing one of the phenyl groups with less lipophilic heterocyclic moieties. The displacement of ({sup 3}H)-N-methyl scopolamine binding by these novel compounds to membranes from cells expressing ml - m4 receptor subtypes was determined. Most of the novel 4-bromo-QNB analogues were potent and slightly selective for ml receptors. The 2-thienyl derivative was the most potent, exhibiting a 2-fold greater potency than BrQNB at ml receptors, and a 4-fold greater potency than BrQNB at ml receptors, and a 4-fold greater potency at m2 receptors. This compound was also considerably less lipophilic than BrQNB as determined from its retention time on C18 reverse phase HPLC. This compound may therefore be useful both for pharmacological studies and as a candidate for a radioiodinated SPECT imaging agent for ml muscarinic receptors in human brain.

Authors:
; ; ;  [1]
  1. (George Washington Univ. Medical Center, Washington, DC (USA))
Publication Date:
OSTI Identifier:
5583540
Resource Type:
Journal Article
Resource Relation:
Journal Name: Life Sciences; (USA); Journal Volume: 48:24
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 62 RADIOLOGY AND NUCLEAR MEDICINE; PARASYMPATHOLYTICS; CHEMICAL PREPARATION; PARASYMPATHOMIMETICS; RECEPTORS; BIOCHEMICAL REACTION KINETICS; BRAIN; RADIOPHARMACEUTICALS; SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY; TRACER TECHNIQUES; TRITIUM COMPOUNDS; AUTONOMIC NERVOUS SYSTEM AGENTS; BODY; CENTRAL NERVOUS SYSTEM; COMPUTERIZED TOMOGRAPHY; DIAGNOSTIC TECHNIQUES; DRUGS; EMISSION COMPUTED TOMOGRAPHY; HYDROGEN COMPOUNDS; ISOTOPE APPLICATIONS; KINETICS; LABELLED COMPOUNDS; MEMBRANE PROTEINS; NERVOUS SYSTEM; ORGANIC COMPOUNDS; ORGANS; PROTEINS; REACTION KINETICS; SYNTHESIS; TOMOGRAPHY; 550201* - Biochemistry- Tracer Techniques; 550601 - Medicine- Unsealed Radionuclides in Diagnostics

Citation Formats

Baumgold, J., Cohen, V.I., Paek, R., and Reba, R.C. Muscarinic receptor subtype selectivity of novel heterocyclic QNB analogues. United States: N. p., 1991. Web. doi:10.1016/0024-3205(91)90269-H.
Baumgold, J., Cohen, V.I., Paek, R., & Reba, R.C. Muscarinic receptor subtype selectivity of novel heterocyclic QNB analogues. United States. doi:10.1016/0024-3205(91)90269-H.
Baumgold, J., Cohen, V.I., Paek, R., and Reba, R.C. Tue . "Muscarinic receptor subtype selectivity of novel heterocyclic QNB analogues". United States. doi:10.1016/0024-3205(91)90269-H.
@article{osti_5583540,
title = {Muscarinic receptor subtype selectivity of novel heterocyclic QNB analogues},
author = {Baumgold, J. and Cohen, V.I. and Paek, R. and Reba, R.C.},
abstractNote = {In an effort at synthesizing centrally-active subtype-selective antimuscarinic agents, the authors derivatized QNB (quinuclidinyl benzilate), a potent muscarinic antagonist, by replacing one of the phenyl groups with less lipophilic heterocyclic moieties. The displacement of ({sup 3}H)-N-methyl scopolamine binding by these novel compounds to membranes from cells expressing ml - m4 receptor subtypes was determined. Most of the novel 4-bromo-QNB analogues were potent and slightly selective for ml receptors. The 2-thienyl derivative was the most potent, exhibiting a 2-fold greater potency than BrQNB at ml receptors, and a 4-fold greater potency than BrQNB at ml receptors, and a 4-fold greater potency at m2 receptors. This compound was also considerably less lipophilic than BrQNB as determined from its retention time on C18 reverse phase HPLC. This compound may therefore be useful both for pharmacological studies and as a candidate for a radioiodinated SPECT imaging agent for ml muscarinic receptors in human brain.},
doi = {10.1016/0024-3205(91)90269-H},
journal = {Life Sciences; (USA)},
number = ,
volume = 48:24,
place = {United States},
year = {Tue Jan 01 00:00:00 EST 1991},
month = {Tue Jan 01 00:00:00 EST 1991}
}
  • Alzheimer's disease (AD) involves selective loss of muscarinic m2, but not m1, subtype neuroreceptors in the posterior parietal cortex of the human brain. Emission tomographic study of the loss of m2 receptors in AD is limited by the fact that there is currently no available m2-selective radioligand which can penetrate the blood-brain barrier. In our efforts to prepare such a radioligand, the authors have used competition studies against currently existing muscarinic receptor radioligands to infer the in vitro and in vivo properties of a novel muscarinic receptor ligand, 5-[[4-[4-(diisobutylamino)butyl]-1-phenyl]acetyl]-10,11-dihydro-5H-dibenzo[b,e][1,4]diazepin-11-one (DIBD). In vitro competition studies against [[sup 3]H](R)-3-quinuclidinylbenzilate ([[sup 3]H]QNB) andmore » [[sup 3]H]N-methylscopolamine ([[sup 3]H]NMS), using membranes derived from transfected cells expressing only m1, m2, m3, or m4 receptor subtypes, indicate that DIBD is selective for m2/m4 over m1/m3. In vivo competition studies against (R,R)-[[sup 125]I]IQNB indicate that DIBD crosses the blood brain barrier (BBB). The relationship of the regional percentage decrease in (R,R)-[[sup 125]I]IQNB versus the percentage of each of the receptor subtypes indicates that DIBD competes more effectively in those brain regions which are known to be enriched in the m2, relative to the m1, m3, and m4, receptor subtype; however, analysis of the data using a mathematical model shows that caution is required when interpreting the in vivo results. The authors conclude that a suitably radiolabeled derivative of DIBD may be of potential use in emission tomographic study of changes in m2 receptors in the central nervous system.« less
  • IQNP, a high affinity muscarinic ligand with high cerebral uptake and long retention, contains two chiral centers in addition to vinyl iodide sterochemistry. The various diastereomers, in which the 3-quinuclidinyl moiety has the R configuration, have been prepared and evaluated in vitro and in vivo. These data show that muscarinic receptor subtype selectivity is dramatically affected by the configuration of the acetate center and vinyl iodide. In vitro studies show that E-(R,R)-IQNP is 100 times more selective for ml than m2 subtype as compared to E-(R,S), which was confirmed by in vivo results. In contrast, in vivo, Z-(R,R) has highmore » uptake in m2 rich tissues (heart and cerebellum). In vitro studies are being performed on the Z isomers. Blocking studies with subtype-specific ligands confirm these data which illustrate the importance of molecular configuration on receptor subtype selectivity. These combined studies demonstrate that these isomers of IQNP are good candidates for future studies of receptor subtypes.« less
  • Alzheimer's disease (AD) involves selective loss of muscarinic m2, but not m1, subtype neuroreceptors in the posterior parietal cortex of the human brain. Emission tomographic study of the loss of m2 receptors in AD is limited by the fact that there is currently no available m2-selective radioligand which can penetrate the blood-brain barrier. [[sup 3]H](R)-3-quinuclidinylbenzilate ([[sup 3]H]QNB) is commonly used for performing in vitro studies of the muscarinic acetylcholine receptor (mAChR), either with membrane homogenates or with autoradiographic slices, in which [[sup 3]H]QNB is nonsubtype-selective. We report here the results of in vivo studies, using both carrier-free and low specificmore » activity [[sup 3]H]QNB, which show that [[sup 3]H]QNB exhibits a substantial in vivo m2-selectivity. Previously reported in vivo (R)-3-quinuclidinyl (R)-4-iodobenzilate ((R,R)-[[sup 125]I]lQNB) binding appears to be nonsubtype-selective. Apparently the bulky iodine substitution in the 4 position reduces the subtype selectivity of QNB. It is possible that a less bulky fluorine substitution might permit retention of the selectivity exhibited by QNB itself. We conclude that a suitably radiolabeled derivative of QNB, possibly labeled with [sup 18]F, may be of potential use in positron emission tomographic (PET) study of the loss of m2 receptors in AD. 39 refs., 8 figs., 2 tab.« less
  • The muscarinic receptor in the rabbit pancreas was characterized with the use of the labeled ligand ({sup 3}H)-(-)-quinuclidinyl-benzylate (({sup 3}H)-(-)-QNB). Specific binding of ({sup 3}H)-(-)-QNB to pancreatic acini was found to be reversible and of high affinity, with an equilibrium dissociation constant (KD) of 68 pmol/l and a receptor density (RT) of 170 fmol/mg protein. Agonist binding behaviour was investigated by displacement of ({sup 3}H)-(-)-QNB binding by eight agonists like arecoline, arecadine-propargylester (APE) and carbachol, yielding only low affinity binding sites. The inhibition of ({sup 3}H)-(-)-QNB binding by the selective antagonists pirenzepine, hexahydrosiladifenidol (HHSiD) and (11-(2-(diethyl-amino)-methyl-1-piperidinyl)acetyl)-5,11-dihydro-6H-pyr ido (2,3-b) (1,4) benzodiazepin-6-onemore » (AF-DX 116) confirmed the M3 nature of the rabbit pancreatic receptor.« less