A potent photoreactive general anesthetic with novel binding site selectivity for GABAA receptors

Abdelrahman R Shalabi; Zhiyi Yu; Xiaojuan Zhou; Youssef Jounaidi; Hanwen Chen; Jiajia Dai; Daniel E Kent; Hua-Jun Feng; Stuart A Forman; Jonathan B Cohen; Karol S Bruzik; Keith W Miller

doi:10.1016/j.ejmech.2020.112261

A potent photoreactive general anesthetic with novel binding site selectivity for GABA_A receptors

Eur J Med Chem. 2020 May 15:194:112261. doi: 10.1016/j.ejmech.2020.112261. Epub 2020 Mar 23.

Authors

Affiliations

¹ Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, 833 South Wood Street, Chicago, IL, 60612, USA.
² Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, MA, 02115, USA. Electronic address: zhiyi_yu@sdu.edu.cn.
³ Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA.
⁴ Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA. Electronic address: hanwen.chen@qq.com.
⁵ Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA. Electronic address: Jiajiadai123@hotmail.com.
⁶ Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA; Department of Health Science, Northeastern University, 360 Huntington Ave, Boston, MA, 02115, USA.
⁷ Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, MA, 02115, USA.
⁸ Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, 32 Fruit Street, Boston, MA, 02114, USA. Electronic address: k_miller@helix.mgh.harvard.edu.

Abstract

The pentameric γ-aminobutyric acid type A receptors (GABA_ARs) are the major inhibitory ligand-gated ion channels in the central nervous system. They mediate diverse physiological functions, mutations in them are associated with mental disorders and they are the target of many drugs such as general anesthetics, anxiolytics and anti-convulsants. The five subunits of synaptic GABA_ARs are arranged around a central pore in the order β-α-β-α-γ. In the outer third of the transmembrane domain (TMD) drugs may bind to five homologous intersubunit binding sites. Etomidate binds between the pair of β - α subunit interfaces (designated as β⁺/α^-) and R-mTFD-MPAB binds to an α⁺/β^- and an γ⁺/β^- subunit interface (a β^- selective ligand). Ligands that bind selectively to other homologous sites have not been characterized. We have synthesized a novel photolabel, (2,6-diisopropyl-4-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenyl)methanol or pTFD-di-iPr-BnOH). It is a potent general anesthetic that positively modulates agonist and benzodiazepine binding. It enhances GABA-induced currents, shifting the GABA concentration-response curve to lower concentrations. Photolabeling-protection studies show that it has negligible affinity for the etomidate sites and high affinity for only one of the two R-mTFD-MPAB sites. Exploratory site-directed mutagenesis studies confirm the latter conclusions and hint that pTFD-di-iPr-BnOH may bind between the α⁺/β^- and α⁺/γ^- subunits in the TMD, making it an α⁺ ligand. The latter α⁺/γ^- site has not previously been implicated in ligand binding. Thus, pTFD-di-iPr-BnOH is a promising new photolabel that may open up a new pharmacology for synaptic GABA_ARs.

Keywords: Diazirine; GABA-A receptor; General anesthetics binding sites; Photolabeling; Positive allosteric modulator; Transmembrane domain.

MeSH terms

Allosteric Regulation / drug effects
Anesthetics, General / chemical synthesis
Anesthetics, General / chemistry
Anesthetics, General / pharmacology*
Animals
Binding Sites / drug effects
Dose-Response Relationship, Drug
HEK293 Cells
Humans
Models, Molecular
Molecular Structure
Photochemical Processes
Propofol / chemical synthesis
Propofol / chemistry
Propofol / pharmacology*
Receptors, GABA-A / metabolism*
Structure-Activity Relationship
Xenopus

Substances

Anesthetics, General
Receptors, GABA-A
Propofol

Grants and funding

P01 GM058448/GM/NIGMS NIH HHS/United States