2. Academic Validation
  3. Delineation of the functional properties and the mechanism of action of TMPPAA, an allosteric agonist and positive allosteric modulator of 5-HT3 receptors

Delineation of the functional properties and the mechanism of action of TMPPAA, an allosteric agonist and positive allosteric modulator of 5-HT3 receptors

  • Biochem Pharmacol. 2016 Jun 15;110-111:92-108. doi: 10.1016/j.bcp.2016.04.004.
Agnes Gasiorek 1,  Sarah M Trattnig 1,  Philip K Ahring 2,  Uffe Kristiansen 1,  Bente Frølund 1,  Kristen Frederiksen 3,  Anders A Jensen 4
Affiliations

Affiliations

  • 1 Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
  • 2 Saniona A/S, Baltorpvej 154, DK-2750 Ballerup, Denmark.
  • 3 H. Lundbeck A/S, Otiliavej 9, DK-2500 Valby, Denmark.
  • 4 Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark. Electronic address: aaj@sund.ku.dk.
PMID: 27086281 DOI: 10.1016/j.bcp.2016.04.004
Abstract

We have previously identified a novel class of 5-hydroxytryptamine type 3 receptor (5-HT3R) agonists sharing little structural similarity with orthosteric 5-HT3R ligands (Jørgensen et al., 2011). In the present study we have elucidated the functional characteristics and the mechanism of action of one of these compounds, trans-3-(4-methoxyphenyl)-N-(pentan-3-yl)acrylamide (TMPPAA). In electrophysiological recordings TMPPAA was found to be a highly-efficacious partial agonist equipotent with 5-HT at the 5-HT3A receptor (5-HT3AR) expressed in COS-7 cells and somewhat less potent at the receptor expressed in Xenopus oocytes. The desensitization kinetics of TMPPAA-evoked currents were very different from those mediated by 5-HT. Moreover, repeated TMPPAA applications resulted in progressive current run-down and persistent non-responsiveness of the receptor to TMPPAA, but not to 5-HT. In addition to its direct activation, TMPPAA potentiated 5-HT-mediated 5-HT3AR signalling, and the allosteric link between the two binding sites was corroborated by the analogous ability of 5-HT to potentiate TMPPAA-evoked responses. The agonism and potentiation exerted by TMPPAA at a chimeric α7-nACh/5-HT3A receptor suggested that the ligand acts through the transmembrane domain of 5-HT3AR, a notion further substantiated by its functional properties at chimeric and mutant human/murine 5-HT3ARs. A residue in the transmembrane helix 4 of 5-HT3A was identified as an important molecular determinant for the different agonist potencies exhibited by TMPPAA at human and murine 5-HT3ARs. In conclusion, TMPPAA is a novel allosteric agonist and positive allosteric modulator of 5-HT3Rs, and its aberrant signalling characteristics compared to 5-HT at the 5-HT3AR underline the potential in Cys-loop receptor modulation and activation through allosteric sites.

Keywords

5-HT(3) receptor; Ago-PAM; Allosteric agonist; Allosteric modulation; Cys-loop receptor; TMPPAA.

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