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Computational Modeling of the AT2 Receptor and AT2 Receptor Ligands: Investigating Ligand Binding, Structure–Activity Relationships, and Receptor-Bound Models
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Medicinal Chemistry, Organic Pharmaceutical Chemistry.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Rational conversion of biologically active peptides to nonpeptide compounds with retained activity is an appealing approach in drug development. One important objective of the work presented in this thesis was to use computational modeling to aid in such a conversion of the peptide angiotensin II (Ang II, Asp-Arg-Val-Tyr-Ile-His-Pro-Phe). An equally important objective was to gain an understanding of the requirements for ligand binding to the Ang II receptors, with a focus on interactions with the AT2 receptor.

The bioactive conformation of a peptide can provide important guidance in peptidomimetic design. By designing and introducing well-defined secondary structure mimetics into Ang II the bioactive conformation can be addressed. In this work, both γ- and β-turn mimetic scaffolds have been designed and characterized for incorporation into Ang II. Using conformational analysis and the pharmacophore recognition method DISCO, a model was derived of the binding mode of the pseudopeptide Ang II analogues. This model indicated that the positioning of the Arg side chain was important for AT2 receptor binding, which was also supported when the structure–activity relationship of Ang II was investigated by performing a glycine scan.

To further examine ligand binding, a 3D model of the AT2 receptor was constructed employing homology modeling. Using this receptor model in a docking study of the ligands, binding modes were identified that were in agreement with data from point-mutation studies of the AT2 receptor.

By investigating truncated Ang II analogues, small pseudopeptides were developed that were structurally similar to nonpeptide AT2 receptor ligands. For further guidance in ligand design of nonpeptide compounds, three-dimensional quantitative structure–activity relationship models for AT1 and AT2 receptor affinity as well as selectivity were derived.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2007. , p. 78
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 54
Keywords [en]
Pharmaceutical chemistry, Angiotensin II, AT1, AT2, SAR, bioactive conformation, turn mimetic, peptidomimetic, DISCO, homology model, 3D-QSAR, CoMFA
Keywords [sv]
Farmaceutisk kemi
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-7823ISBN: 978-91-554-6867-5 (print)OAI: oai:DiVA.org:uu-7823DiVA, id: diva2:170109
Public defence
2007-05-11, B41, BMC, Husargatan 3, Uppsala, 13:15
Opponent
Supervisors
Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2012-05-16Bibliographically approved
List of papers
1. A Selective AT2 Receptor Ligand with a γ-Turn-Like Mimetic replacing the Amino Acid Residues 4-5 of Angiotensin II
Open this publication in new window or tab >>A Selective AT2 Receptor Ligand with a γ-Turn-Like Mimetic replacing the Amino Acid Residues 4-5 of Angiotensin II
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2004 (English)In: Journal of Medicinal Chemistry, ISSN 0022-2623, E-ISSN 1520-4804, Vol. 47, no 4, p. 859-870Article in journal (Refereed) Published
Abstract [en]

Three angiotensin II (Ang II) analogues encompassing a benzodiazepine-based γ-turn-like scaffold have been synthesized. Evaluation of the compounds in a radioligand binding assay showed that they had no affinity to the rat liver AT1 receptor. However, one of the compounds displayed considerable affinity to the pig uterus AT2 receptor (Ki = 3.0 nM) while the other two lacked affinity to this receptor. It was hypothesized that the reason for the inactivity of one of these analogues to the AT2 receptor was that the guanidino group of the Arg2 residue and/or the N-terminal end of the pseudopeptide could not interact optimally with the receptor. To investigate this hypothesis, a conformational analysis was performed and a comparison was carried out with the monocyclic methylenedithioether analogue cyclo(S−CH2−S)[Cys3,5]Ang II which is known to bind with high affinity to the AT2 receptor (Ki = 0.62 nM). This comparison showed that, in the compounds with high AT2 receptor affinity, the guanidino group of the Arg2 residue and the N-terminal end could access common regions of space that were not accessible to the inactive compound. To examine the importance of the guanidino group for binding, the Arg side chain was removed by substituting Arg2 for Ala2 in the analogue having the high affinity. This analogue lacked affinity to AT2 receptors, which supports the role of the guanidino group in receptor binding.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-92323 (URN)10.1021/jm030921v (DOI)
Available from: 2004-11-10 Created: 2004-11-10 Last updated: 2017-12-14Bibliographically approved
2. Synthesis and AT2 receptor-binding properties of angiotensin II analogues
Open this publication in new window or tab >>Synthesis and AT2 receptor-binding properties of angiotensin II analogues
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2004 (English)In: Journal of Peptide Research, ISSN 1397-002X, E-ISSN 1399-3011, Vol. 64, no 5, p. 194-201Article in journal (Refereed) Published
Abstract [en]

The present study investigates the importance of the amino acid side chains in the octapeptide angiotensin II (Ang II) for binding to the AT2 receptor. A Gly scan was performed where each amino acid in Ang II was substituted one-by-one with glycine. The resulting set of peptides was tested for affinity to the AT2 receptor (porcine myometrial membranes). For a comparison, the peptides were also tested for affinity to the AT1 receptor (rat liver membranes). Only the substitution of Arg2 reduced affinity to the AT2 receptor considerably (92-fold when compared with Ang II). For the other Gly-substituted analogues the affinity to the AT2 receptor was only moderately affected. To further investigate the role of the Arg2 side chain for receptor binding, we synthesized some N-terminally modified Ang II analogues. According to these studies a positive charge in the N-terminal end of angiotensin III [Ang II (2–8)] is not required for high AT2 receptor affinity but seems to be more important in Ang II. With respect to the AT1 receptor, [Gly2]Ang II and [Gly8]Ang II lacked binding affinity (Ki > 10 μm). Replacement of the Val3 or Ile5 residues with Gly produced only a slight decrease in affinity. Interestingly, substitution of Tyr4 or His6, which are known to be very important for AT1 receptor binding, resulted in only 48 and 14 times reduction in affinity, respectively.

Keywords
angiotensin II, angiotensin III, AT1 binding, AT2 binding, Gly scan, peptide synthesis, structure–activity relationship
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-92324 (URN)10.1111/j.1399-3011.2004.00184.x (DOI)
Available from: 2004-11-10 Created: 2004-11-10 Last updated: 2017-12-14Bibliographically approved
3. New selective AT2 receptor ligands encompassing a γ-turn mimetic replacing the amino acid residues 4-5 of angiotensin II act as agonists
Open this publication in new window or tab >>New selective AT2 receptor ligands encompassing a γ-turn mimetic replacing the amino acid residues 4-5 of angiotensin II act as agonists
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2005 (English)In: Journal of Medicinal Chemistry, ISSN 0022-2623, E-ISSN 1520-4804, Vol. 48, no 12, p. 4009-4024Article in journal (Refereed) Published
Abstract [en]

New benzodiazepine-based γ-turn mimetics with one or two amino acid side chains were synthesized. The γ-turn mimetics were incorporated into angiotensin II (Ang II) replacing the Val3-Tyr4-Ile5 or Tyr4-Ile5 peptide segments. All of the resulting pseudopeptides displayed high AT2/AT1 receptor selectivity and exhibited AT2 receptor affinity in the low nanomolar range. Molecular modeling was used to investigate whether the compounds binding to the AT2 receptor could position important structural elements in common areas. A previously described benzodiazepine-based γ-turn mimetic with high affinity for the AT2 receptor was also included in the modeling. It was found that the molecules, although being structurally quite different, could adopt the same binding mode/interaction pattern in agreement with the model hypothesis. The pseudopeptides selected for agonist studies were shown to act as AT2 receptor agonists being able to induce outgrowth of neurite cells, stimulate p42/p44mapk, and suppress proliferation of PC12 cells.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-95767 (URN)10.1021/jm0491492 (DOI)
Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2017-12-14Bibliographically approved
4. Angiotensin II Pseudopeptides Containing 1,3,5-Trisubstituted Benzene Scaffolds with High AT2 Receptor Affinity
Open this publication in new window or tab >>Angiotensin II Pseudopeptides Containing 1,3,5-Trisubstituted Benzene Scaffolds with High AT2 Receptor Affinity
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2005 (English)In: Journal of Medicinal Chemistry, ISSN 0022-2623, E-ISSN 1520-4804, Vol. 48, no 21, p. 6620-6631Article in journal (Refereed) Published
Abstract [en]

Two 1,3,5-trisubstituted aromatic scaffolds intended to serve as γ-turn mimetics have been synthesized and incorporated in five pseudopeptide analogues of angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe), replacing Val-Tyr-Ile, Val-Tyr, or Tyr-Ile. All the tested compounds exhibited nanomolar affinity for the AT2 receptor with the best compound (3) having a Ki of 1.85 nM. Four pseudopeptides were AT2 selective, while one (5) also exhibited good affinity for the AT1 receptor (Ki = 30.3 nM). This pseudopeptide exerted full agonistic activity in an AT2 receptor induced neurite outgrowth assay but displayed no agonistic effect in an AT1 receptor functional assay. Molecular modeling, using the program DISCOtech, showed that the high-affinity ligands could interact similarly with the AT2 receptor as other ligands with high affinity for this receptor. A tentative agonist model is proposed for AT2 receptor activation by angiotensin II analogues. We conclude that the 1,3,5-trisubstituted benzene rings can be conveniently prepared and are suitable as γ-turn mimics.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-95768 (URN)10.1021/jm050280z (DOI)
Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2017-12-14Bibliographically approved
5. Design, synthesis, and incorporation of a beta-turn mimetic in angiotensin II forming novel pseudopeptides with affinity for AT(1) and AT(2) receptors
Open this publication in new window or tab >>Design, synthesis, and incorporation of a beta-turn mimetic in angiotensin II forming novel pseudopeptides with affinity for AT(1) and AT(2) receptors
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2006 (English)In: Journal of Medicinal Chemistry, ISSN 0022-2623, E-ISSN 1520-4804, Vol. 49, no 20, p. 6133-6137Article in journal (Refereed) Published
Abstract [en]

A benzodiazepine-based beta-turn mimetic has been designed, synthesized, and incorporated into angiotensin II. Comparison of the mimetic with beta-turns in crystallized proteins showed that it most closely resembles a type II beta-turn. The compounds exhibited high to moderate binding affinity for the AT(2) receptor, and one also displayed high affinity for the AT(1) receptor. Molecular modeling showed that the high-affinity compounds could be incorporated into a previously derived model of AT(2) receptor ligands.

National Category
Pharmaceutical Sciences
Identifiers
urn:nbn:se:uu:diva-95769 (URN)10.1021/jm051222g (DOI)000240826200029 ()17004728 (PubMedID)
Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2018-01-13Bibliographically approved
6. Modeling binding modes of angiotensin II and pseudopeptide analogues to the AT2 receptor
Open this publication in new window or tab >>Modeling binding modes of angiotensin II and pseudopeptide analogues to the AT2 receptor
2008 (English)In: Journal of Molecular Graphics and Modelling, ISSN 1093-3263, E-ISSN 1873-4243, Vol. 26, no 6, p. 991-1003Article in journal (Refereed) Published
Abstract [en]

The 3D model of the AT(2) receptor has been built employing homology to the transmembrane domain of rhodopsin and a novel build-up procedure for restoring the extracellular loops. By docking a model peptide of angiotensin II in the AT(2) receptor model two plausible binding modes were identified. These binding modes were in agreement with most of the suggested ligand-receptor contact points reported in the literature. Eight active and one inactive pseuclopeptide angiotensin II analogue were also docked in the receptor and four of the active pseudopeptides were found to mimic the binding mode of angiotensin II. An alternative binding mode for the other four active pseudopeptides was found.

Keywords
AT(2) receptor, angiotensin II, homology modeling, docking, bioactive conformation
National Category
Pharmaceutical Sciences
Identifiers
urn:nbn:se:uu:diva-95770 (URN)10.1016/j.jmgm.2007.08.005 (DOI)000253068700012 ()17936050 (PubMedID)
Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2022-01-28Bibliographically approved
7. Synthesis of a new class of druglike angiotensin II C-terminal mimics with affinity for the AT2 receptor
Open this publication in new window or tab >>Synthesis of a new class of druglike angiotensin II C-terminal mimics with affinity for the AT2 receptor
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2007 (English)In: Journal of Medicinal Chemistry, ISSN 0022-2623, E-ISSN 1520-4804, Vol. 50, no 7, p. 1711-1715Article in journal (Refereed) Published
Abstract [en]

Four tripeptides corresponding to the C-terminal region of angiotensin II were synthesized. One of these peptides (Ac-His-Pro-Ile) showed moderate binding affinity for the AT2 receptor. Two aromatic histidine-related scaffolds were synthesized and introduced in the tripeptides to give eight new peptidomimetic structures. Three of the new peptide-derived druglike molecules exhibited selective, nanomolar affinity for the AT2 receptor. These ligands may become lead compounds in the future development of novel classes of selective AT2 receptor agonists.

National Category
Pharmaceutical Sciences
Identifiers
urn:nbn:se:uu:diva-95771 (URN)10.1021/jm0613469 (DOI)000245259000033 ()17358051 (PubMedID)
Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2018-01-13Bibliographically approved
8. Development of CoMFA models of affinity and selectivity to angiotensin II type-1 and type-2 receptors
Open this publication in new window or tab >>Development of CoMFA models of affinity and selectivity to angiotensin II type-1 and type-2 receptors
2007 (English)In: Journal of Molecular Graphics and Modelling, ISSN 1093-3263, E-ISSN 1873-4243, Vol. 26, no 1, p. 145-153Article in journal (Refereed) Published
Abstract [en]

The renin-angiotensin system (RAS) is of major importance in cardiovascular and renal regulation and has been an attractive target in drug discovery for a long time. The main receptors involved in the RAS are the Angiotensin type-1 (AT1) and type-2 (AT2) receptors, which are both activated by the endogenous octapeptide angiotensin II (AngII). This study describes the development of 3D-QSAR models for AT1 and AT2 receptor affinity and AT1/AT2 receptor selectivity using CoMFA. A data set of 244 compounds, based on the triazolinone and quinazolinone structural classes was compiled from the literature. Before CoMFA could be performed, an alignment rule for the two structural classes was defined using the pharmacophore-searching program DISCOtech. Models were validated using a test set obtained by dividing the data set into a training set and test set using hierarchical clustering, based on the CoMFA fields, AT1-, AT2-receptor affinities, and AT1/AT2 selectivity values. Predictive models with good statistics could be developed both for AT1 and AT2 receptor affinity as well as selectivity towards these receptors.

Keywords
Angiotensin, AT1, AT2, Selectivity, CoMFA, 3D-QSAR, DISCOtech, Training set selection
National Category
Pharmaceutical Sciences
Identifiers
urn:nbn:se:uu:diva-95772 (URN)10.1016/j.jmgm.2006.10.004 (DOI)000248646500014 ()17161636 (PubMedID)
Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2018-01-13Bibliographically approved

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