Novel 17β-Substituted Conformationally Constrained Neurosteroids that Modulate GABA_A Receptors

Abstract

The goal of this study was to develop a series of allopregnanolone analogues substituted by conformationally constrained 17beta side chains to obtain additional information about the structure-activity relationship of 5alpha-reduced steroids to modulate GABA(A) receptors. Specifically, we introduced alkynyl-substituted 17beta side chains in which the triple bond is either directly attached to the 17beta-position or to the 21-position of the steroid skeleton. Furthermore, we investigated the effects of C22 and C20 modification. The in vitro binding affinity for the GABA(A) receptor of the new analogues was measured by allosteric displacement of the specific binding of [(3)H]4'-ethynyl-4-n-propyl-bicycloorthobenzoate (EBOB) to GABA(A) receptors on synaptosomal membranes of rat cerebellum. An allosteric binding model that has been successfully applied to ionotropic glycine receptors was employed. The most active derivative is (20R)-17beta-(1-hydroxy-2,3-butadienyl)-5alpha-androstane-3-ol (20), which possesses low nanomolar potency to modulate cerebellar GABA(A) receptors and is 71 times more active than the control compound allopregnanolone. Theoretical conformational analysis was employed in an attempt to correlate the in vitro results with the active conformations of the most potent of the new analogues.

Structure-Activity Relationships of Neuroactive Steroids Acting on the GABAA Receptor

“…Displacement of the specific binding of [ 3 H]-4´-ethynyl-4-n-propyl-bicycloorthobenzoate ([ 3 H]EBOB) follows an allosteric binding model that was first applied to glycine receptors which belong to the same superfamily of transmitter-gated ion channels as the GABA A receptor. Recently this binding assay was successfully used on GABA A receptors on synaptosomal membranes of rat cerebellum [17].…”

“…Most of the work has been focused on functional changes of the 17-substituent and in the search for preferred orientations of the side chain that would help to map the interacting part of the receptor. A series of natural and synthetic 3 -hydroxy steroids (both 5 and 5 ) with various side chains (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) were tested for their ability to potentiate muscimol-stimulated 36 Cl -uptake ( Relative potency represents the relative rate of 36 Cl -uptake in the presence of steroid and muscimol, compared to that produced by muscimol and allotetrahydroDOC (3).…”

“…Souli and coworkers, developed another series of allopregnanolone (1) analogues with rigid free rotating 17 side chains (46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57) [17]. Specifically they introduced alkynyl and propadienyl functionalities at positions C-17 and C-20 of the steroid skeleton and also investigated the effects of C-22 and C-20 modifications.…”

Allene as an Alternative Functional Group for Drug Design: Effect of CC Multiple Bonds Conjugated with Quinazolines on the Inhibition of EGFR Tyrosine Kinase

“…[4] An allenic derivative of the neurosteroid allopregnanolone possesses anticonvulsant and anxiolytic activity. [5,6] Allopregnanolone has been reported to be a potent positive allosteric modulator of g-aminobutyric acid (GABA) action at the GABA A receptor, [7] and introduction of an allene group onto allopregnanolone potently increased GABA A receptor modulating activity, with 70-fold greater efficacy than allopregnanolone itself. [5] Epidermal growth factor receptor (EGFR) tyrosine kinase plays a fundamental role in signal transduction pathways.…”

“…[5,6] Allopregnanolone has been reported to be a potent positive allosteric modulator of g-aminobutyric acid (GABA) action at the GABA A receptor, [7] and introduction of an allene group onto allopregnanolone potently increased GABA A receptor modulating activity, with 70-fold greater efficacy than allopregnanolone itself. [5] Epidermal growth factor receptor (EGFR) tyrosine kinase plays a fundamental role in signal transduction pathways. EGFR and its ligands (EGF and TGF-a) have been implicated in numerous tumors of epithelial origin [8,9] and proliferative disorders of the epidermis such as psoriasis.…”