Thermodynamic Characterization of New Positive Allosteric Modulators Binding to the Glutamate Receptor A2 Ligand-Binding Domain: Combining Experimental and Computational Methods Unravels Differences in Driving Forces

Abstract

Positive allosteric modulation of the ionotropic glutamate receptor GluA2 presents a potential treatment of cognitive disorders, for example, Alzheimer's disease. In the present study, we describe the synthesis, pharmacology, and thermodynamic studies of a series of monofluoro-substituted 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides. Measurements of ligand binding by isothermal titration calorimetry (ITC) showed similar binding affinities for the modulator series at the GluA2 LBD but differences in the thermodynamic driving forces. Binding of 5c (7-F) and 6 (no-F) is enthalpy driven, and 5a (5-F) and 5b (6-F) are entropy driven. For 5d (8-F), both quantities were equal in size. Thermodynamic integration (TI) and one-step perturbation (OSP) were used to calculate the relative binding affinity of the modulators. The OSP calculations had a higher predictive power than those from TI, and combined with the shorter total simulation time, we found the OSP method to be more effective for this setup. Furthermore, from the molecular dynamics simulations, we extracted the enthalpies and entropies, and along with the ITC data, this suggested that the differences in binding free energies are largely explained by the direct ligand-surrounding enthalpies. Furthermore, we used the OSP setup to predict binding affinities for a series of polysubstituted fluorine compounds and monosubstituted methyl compounds and used these predictions to characterize the modulator binding pocket for this scaffold of positive allosteric modulators.

7-Phenoxy-Substituted 3,4-Dihydro-2H-1,2,4-benzothiadiazine 1,1-Dioxides as Positive Allosteric Modulators of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors with Nanomolar Potency

“…19,20 While the introduction of the cyclopropyl group in this position was clearly the optimal choice and could thus not be neglected, we decided to also investigate the impact of the insertion of the smallest alkyl radical, namely the methyl group.…”

Identification and Structure-Function Study of Positive Allosteric Modulators of Kainate Receptors

“…Novel 1,2,4-benzothiadiazine 1,1-dioxides (BTDs), which are structurally related to the BTD reference compound 7-chloro-3-methyl-3,4-dihydro-2H-1,2,4benzothiadiazine 1,1-dioxide (IDRA21) ( Fig. 1), act as positive allosteric modulators of the AMPARs (Francotte et al, 2007(Francotte et al, , 2008(Francotte et al, , 2010(Francotte et al, , 2013(Francotte et al, , 2014Krintel et al, 2012Krintel et al, , 2016Nørholm et al, 2013Nørholm et al, , 2014Larsen et al, 2016). Starting from IDRA21, removal of the methyl group at the 3-position and introduction of a short alkyl chain at the 4-position of the BTD scaffold was responsible for a marked improvement of in vitro and in vivo activity on AMPARs, as was observed with 7-halo-substituted compounds, such as the 7-fluoro derivative 4-ethyl-7-fluoro-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide (BPAM97) (Francotte et al, 2007).…”

“…A more recent evolution occurred with the discovery of potent AMPAR modulators, such as 4-cyclopropyl-7-hydroxy-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide (BPAM521), bearing a hydroxyl group at the 7-position of the heterocycle (Krintel et al, 2016). Several of the BTDs were cocrystallized with the LBD of the GluA2 subunit of AMPARs, showing that all of these compounds have the same binding mode at the level of the LBD dimer interface (Krintel et al, 2012(Krintel et al, , 2016Nørholm et al, 2013Nørholm et al, , 2014Francotte et al, 2014;Larsen et al, 2016). Due to structural analogy between AMPARs and KARs, we tested whether the structurally simple and low-molecularweight compounds BPAM121, BPAM344, and BPAM521 may act as possible positive allosteric modulators of KARs.…”

AMPA Receptor Positive Allosteric Modulators: Potential for the Treatment of Neuropsychiatric and Neurological Disorders

“…A number of groups at the universities of Liege, Copenhagen and Modena have published work centred around the thiadiazine template 5. [131][132][133][134][135][136][137][138] Servier also worked for many years on this template but have not described any new chemotypes related to this scaffold in the period covered by this article. This work has been comprehensively reviewed elsewhere.…”