RT Journal Article
SR Electronic
T1 Differing activity profiles of the stereoisomers of 2,3,5,6TMP-TQS, a putative silent allosteric modulator of α7nAChR
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP mol.120.119958
DO 10.1124/mol.120.119958
A1 Roger L Papke
A1 Sumanta Garai
A1 Clare Stokes
A1 Nicole A Horenstein
A1 Arthur D Zimmerman
A1 Khalil A Abboud
A1 Ganesh A Thakur
YR 2020
UL http://molpharm.aspetjournals.org/content/early/2020/07/17/mol.120.119958.abstract
AB Abstract: Many synthetic compounds to which we attribute specific activities are produced as racemic mixtures of stereoisomers, and it may be that all of the desired activity comes from a single enantiomer. We have previously shown this to be the case with the α7 nicotinic acetylcholine receptor positive allosteric modulator (PAM) TQS, and the α7 ago-PAM 4BP-TQS. 2,3,5,6TMP-TQS, previously published as a "silent allosteric modulator" and an antagonist of α7 allosteric activation, shares the same scaffold with three chiral centers as the aforementioned compounds. We isolated the enantiomers of 2,3,5,6TMP-TQS and determined that the (-) isomer was a significantly better antagonist than the (+) isomer of the allosteric activation of both wild-type α7 and the non-orthosterically activatible C190A α7 mutant by the ago-PAM GAT107 (the active isomer of 4BP-TQS). In contrast (+)2,3,5,6TMP-TQS proved to be an α7 PAM. (-)2,3,5,6TMP-TQS was shown to antagonize the allosteric activation of α7 by the structurally unrelated ago-PAM B-973B, as well as the allosteric activation of the TQS-sensitive α4β2L15'M mutant. In silico docking of 2,3,5,6TMP-TQS in the putative allosteric activation binding site suggested a specific interaction of the (-) enantiomer with α7T106, and allosteric activation of α7T106 mutants was not inhibited by (-)2,3,5,6TMP-TQS, confirming the importance of this interaction and supporting the model of the allosteric binding site. Comparisons and contrasts between 2,3,5,6TMP-TQS isomers and active and inactive enantiomers of other TQS-related compounds identify the orientation of the cyclopentenyl ring to the plane of the core quinoline to be a crucial determinate of PAM activity.SIGNIFICANCE STATEMENT Significance statement Alpha7-type nicotinic acetylcholine receptors are important and challenging therapeutic targets. Their activity is controlled by orthosteric ligands that function as agonists, partial agonists, and antagonists. However, recently new generations of allosteric ligands have been developed that offer both new therapeutic approaches and new tools for understanding the complex functional dynamics of these receptors. Many of these synthetic ligands are in use as racemic preparations, where the individual enantiomers may have contrasting properties that can confound the interpretation of the results. We demonstrate this to be the case with a TQS analog that was originally reported to lack activity as a positive allosteric modulator (PAM), when actually one enantiomer is a PAM and the other is an allosteric antagonist. This work illustrates the importance of working with specific isomers. Furthermore, our in silico studies and structural comparisons identify essential elements of both the allosteric ligands and receptor binding sites important for allosteric activity.