Interaction of amoxapine with muscarinic cholinergic receptors: an in vitro assessment

Telescoped synthesis of C3-functionalized (E)-arylamidines using Ugi-Mumm and regiospecific quinazolinone rearrangements

An efficient four-step, six-transformation protocol was developed to afford bioactive N-alkyl- or N-arylamide (E)-arylamidines featuring strategic amidine C3 modifications which were inaccessible or low yielding by previous methods. This synthetic approach, exemplified with 24 amidines and requiring only a single purification, highlights a multicomponent Ugi-Mumm rearrangement to afford highly diversified quinazolinones which undergo regiospecific rearrangement to afford new amidines. The method extensively broadens the structural scope of this new class of trisubstituted amidines and demonstrates the tolerance of regional C3 amidine steric bulk, visualized with X-ray crystallographic analysis.

Chemical structural novelty: on-targets and off-targets

Drug structures may be quantitatively compared based on 2D topological structural considerations and based on 3D characteristics directly related to binding. A framework for combining multiple similarity computations is presented along with its systematic application to 358 drugs with overlapping pharmacology. Given a new molecule along with a set of molecules sharing some biological effect, a single score based on comparison to the known set is produced, reflecting either 2D similarity, 3D similarity, or their combination. For prediction of primary targets, the benefit of 3D over 2D was relatively small, but for prediction of off-targets, the added benefit was large. In addition to assessing prediction, the relationship between chemical similarity and pharmacological novelty was studied. Drug pairs that shared high 3D similarity but low 2D similarity (i.e., a novel scaffold) were shown to be much more likely to exhibit pharmacologically relevant differences in terms of specific protein target modulation.

Chem2Bio2RDF: a semantic framework for linking and data mining chemogenomic and systems chemical biology data

Background

Recently there has been an explosion of new data sources about genes, proteins, genetic variations, chemical compounds, diseases and drugs. Integration of these data sources and the identification of patterns that go across them is of critical interest. Initiatives such as Bio2RDF and LODD have tackled the problem of linking biological data and drug data respectively using RDF. Thus far, the inclusion of chemogenomic and systems chemical biology information that crosses the domains of chemistry and biology has been very limited

Results

We have created a single repository called Chem2Bio2RDF by aggregating data from multiple chemogenomics repositories that is cross-linked into Bio2RDF and LODD. We have also created a linked-path generation tool to facilitate SPARQL query generation, and have created extended SPARQL functions to address specific chemical/biological search needs. We demonstrate the utility of Chem2Bio2RDF in investigating polypharmacology, identification of potential multiple pathway inhibitors, and the association of pathways with adverse drug reactions.

Conclusions

We have created a new semantic systems chemical biology resource, and have demonstrated its potential usefulness in specific examples of polypharmacology, multiple pathway inhibition and adverse drug reaction - pathway mapping. We have also demonstrated the usefulness of extending SPARQL with cheminformatics and bioinformatics functionality.

PubChem as a source of polypharmacology

Polypharmacology provides a new way to address the issue of high attrition rates arising from lack of efficacy and toxicity. However, the development of polypharmacology is hampered by the incomplete SAR data and limited resources for validating target combinations. The PubChem bioassay collection, reporting the activity of compounds in multiple assays, allows us to study polypharmacological behavior in the PubChem collection via cross-assay analysis. In this paper, we developed a network representation of the assay collection and then applied a bipartite mapping between this network and various biological networks (i.e., PPI, pathway) as well as artificial networks (i.e., drug-target network). Mapping to a drug-target network allows us to prioritize new selective compounds, while mapping to other biological networks enable us to observe interesting target pairs and their associated compounds in the context of biological systems. Our results indicate this approach could be a useful way to investigate polypharmacology in the PubChem bioassay collection.

Alpha 1-adrenoceptor subtype in the rat prostate is preferentially the alpha 1A type

alpha 1-Adrenoceptors in the rat prostate were characterized by a binding assay using the newly synthesized radioligand [3H]-YM617 (5-[2-[[2[ethoxyring(n)-3H](o-ethoxyphenoxy)ethyl]amino]prop yl]-2-methoxybenzenesulfonamide HCl) and an in vitro assay. Specific [3H]-YM617 binding in the rat prostate was saturable and of high affinity (KD = 61.5 +/- 5.9 pM) with 23.2 +/- 6.9 fmol/mg of protein as the maximal number of binding sites (Bmax). alpha-Adrenoceptor agonists and antagonists inhibited the binding of the radioligand with the following order of effectiveness: YM617 > prazosin = bunazosin > WB4101 > 5-methylurapidil = phenoxybenzamine > phentolamine > S(+)-isomer of YM617 > yohimbine > norepinephrine > phenylephrine > methoxamine. alpha 1-Adrenoceptors in the rat prostate preferred the R(-)-isomer of YM617 to the S(+)-isomer. Preincubation with chlorethylclonidine (CEC; 10(-5) M, 10 min) just slightly changed the Bmax value for [3H]-YM617 without changing the KD value in the prostate; however, CEC reduced the Bmax in the aorta. In the isolated tissue, pretreatment with CEC (10(-5) M, 10 and 30 min) time-dependently shifted to the right the dose-response curve for phenylephrine and decreased the maximal contraction of aortas induced by phenylephrine, but did not shift or decrease those of prostates. The present results indicate that the alpha 1-adrenoceptors in the rat prostate are mainly CEC-insensitive (alpha 1A), whereas those in the aorta are CEC-sensitive (alpha 1B).

A comparison of the effects of single doses of amoxapine and amitriptyline on autonomic functions in healthy volunteers

We have studied the effects of single oral doses of amoxapine (100 mg and 200 mg), amitriptyline (50 mg and 100 mg), and placebo on some autonomic functions in ten healthy volunteers, using a balanced double-blind crossover design. Amitriptyline significantly reduced salivation and it significantly attenuated both miosis evoked by locally applied pilocarpine and sweat secretion evoked by locally applied carbachol. Amoxapine did not significantly alter any of these measures. Neither treatment significantly altered the pupillary light reflex (latency, amplitude, or 75% recovery time). Resting pupil diameter was significantly reduced by the higher dose of amoxapine but was not affected by the other treatments. The higher dose of amoxapine significantly increased supine systolic blood pressure, but did not affect heart rate or diastolic blood pressure; amitriptyline had no effect on any of these cardiovascular measures. These results confirm the antimuscarinic effects of amitriptyline in man, but provide no evidence for antimuscarinic effects of amoxapine.

Non-selectivity of amitriptyline for subtypes of brain muscarinic receptors demonstrated in binding and functional assays

The characteristics of interaction of amitriptyline, a tricyclic antidepressant, with rat brain muscarinic receptors were assessed using both radioligand binding and functional assays. In competition studies, amitriptyline displaced muscarinic ligand binding from a single high-affinity site in homogenates of various brain regions which have a different distribution of M1 and M2 receptor subtypes. The affinity of amitriptyline for muscarinic receptors was also comparable in all brain regions. Furthermore, amitriptyline identified a single species of muscarinic receptors in intact cells dissociated from the cerebral cortex and in cerebrocortical slices. The non-selectivity of amitriptyline for muscarinic receptor subtypes in these preparations was in contrast to the selectivity exhibited by pirenzepine. This non-selective nature of amitriptyline was also evident in functional assays, since this antidepressant was equipotent at antagonizing M1-mediated increase in phosphoinositide hydrolysis and M2-mediated inhibition of cyclic AMP formation in dissociated cortical cells. Atropine was also equipotent at blocking both responses but was 20- to 30-fold more potent than amitriptyline. These results demonstrate that amitriptyline behaves as a non-selective muscarinic antagonist using both radioligand binding and functional measurements.

Cholinergic properties of desipramine and amoxapine: assessment using a thermoregulation paradigm

1. The withdrawal of tricyclic antidepressants (TCAs) produces symptoms suggesting cholinergic rebound. 2. Amitriptyline (AMI), the most potent antimuscarinic agent among this class of drugs, produces supersensitivity to the muscarinic agonist, oxotremorine. 3. Enhancement of the sensitivity of cholinoceptive neurons to acetylcholine as a consequence of treatment with TCAs would account for many of the symptoms following the withdrawal of these drugs. 4. Desipramine (DMI) is the least potent antimuscarinic compound among the TCAs, yet its withdrawal produces withdrawal symptoms. 5. Recently, it was reported that amoxapine (AMX) weakly binds to muscarinic acetylcholine receptors (mAchR) in vitro. This may indicate that this drug lacks the effects antimuscarinic effects in vivo, and that it will not supersensitize cholinergic networks. 6. A thermoregulation paradigm was used to assess the sensitivity of a central muscarinic mechanism to oxotremorine before and after treatment with DMI and AMX. Treatment with either drug increased the hypothermic response to this agonist. 7. Mechanisms whereby drugs can produce cholinergic system supersensitivity, and the use of thermoregulation paradigms in assessing the properties of therapeutic agents is discussed.