OPUS 2014/13/B/NZ7/02210

Research objectives

In recent years reports of high-affinity non-basic ligands of serotonin receptors – mainly 5-HT6 subtype have been published. For over 20 years the need for the presence of a nitrogen atom in the structure of monoaminergic receptor ligands was considered essential. The primary goal of this project is to clarify the interactions of non-basic ligands with the 5-HT6R binding pocket. Additionally, a hypothesis of allosteric 5-HT6 receptor modulation by non-basic ligands will be experimentally verified.
Our main hypothesis concerns the balance of the required strength of interactions in the binding pocket, i.e. the removal of a very important group for interaction with the receptor binding pocket (basic nitrogen) must be balanced by other intermolecular interactions such as van der Waals forces, hydrogen bonds.

Methodology

For many years extensive search for 5-HT6R ligands have been carried out in the Department of Medicinal Chemistry Institute of Pharmacology PAS. During the systematic research studies the short two series of non-basic 5-HT6R ligands were synthesized. To fully and reliably explain the phenomenon of such ligand interactions with the 5-HT6R a larger group of structurally diverse compounds should be examined.
In this project we intend to synthesize a series of about 80 compounds: known 5-HT6R ligands together with their non-basic counterparts (Task 1). The number of ligands needed was estimated on the results of hierarchical structural clustering of a database, that has been developed in Department of Medicinal Chemistry, consisting of 4480 5-HT6R structures. For all of the obtained compounds the affinity for 5-HT6 receptors will be determined in radioligand binding experiments. In order to define selectivity of synthesized non-basic analogues, an affinity measurement to other monoaminergic receptors (5-HT1A, 5-HT2A, 5-HT7, D2) will be assessed. To determine putative allosteric activity of non-basic ligands, a functional test assay will be performed (Task 2).
In the next step, compounds with a basic nitrogen atom described in literature as well as their new non-basic counterparts (Task 1) will be docked to the 5-HT6R homology models in order to compare binding modes for both classes of ligands (Task 3). The results of binding experiments
will provide the basis for further pharmacophore model development in receptor-based approach (Task 3). Additionally, for selected (about 20) compounds, crystal structure investigation of the basic and non-basic ligands of the 5HT6 receptor will be performed. This study will bring information about conformational differences between basic and non-basic analogues of 5-HT6 receptor ligands. The observed changes in conformation may explain differences in the binding affinity as well as give the reason of the ligand’s activity modification (Task 5).
Task 4 includes a compilation of all data in order to verify hypotheses and to establish the essence of the interaction phenomenon between the non-basic ligands and 5-HT6R.

Expected impact of the project on the development of science, civilization and society

There have been few groups of non-basic 5-HT6R ligands published till date and only two papers describing attempts to elucidate the mechanism of neutral ligand binding. Nevertheless, both publications failed to find a general mechanism, due to very narrow set of structurally similar examplary compounds.
The scientific community is greatly interested in results of these experiments as it will support an exploration of new active substances, not only against the 5-HT6R, but of all monoaminergic receptor GPCRs. In addition, they can make a significant contribution to the understanding of the regulation mechanism of the 5-HT receptors activity.

Principal Investigator

Prof. Andrzej Bojarski

Andrzej Bojarski, Prof.

e-mail: bojarski@if-pan.krakow.pl

phone: +4812 66 23 365

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Executors

Ryszard Bugno, PhD

Ryszard Bugno, PhD

e-mail: bugno@if-pan.krakow.pl

phone: +4812 66 23 320

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Jakub Staroń, MSc

Jakub Staroń, MSc

e-mail: staron@if-pan.krakow.pl

phone: +4812 66 23 320

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Adam Hogendorf, MSc

Adam Hogendorf, MSc

e-mail: ahogendorf@gmail.com

phone: +4812 66 23 320

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Dawid Warszycki, MSc

Dawid Warszycki, MSc

e-mail: warszyc@if-pan.krakow.pl

phone: +4812 66 23 301

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Grzegorz Satała, MSc

Grzegorz Satała, MSc

e-mail: satala@if-pan.krakow.pl

phone: +4812 66 23 301

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