BACKGROUND: Receptor tyrosine kinases (RTK) act through dimerization. Previously it was thought that only bivalent ligands could be agonistic, whereas monovalent ligands should be antagonistic. This notion changed after the demonstration that monovalent ligands can be agonistic, including our report of a small molecule monovalent ligand "D3" that is a partial agonist of the NGF receptor TrkA. A bivalent "D3-linker-D3" was expected to increase agonism. METHODS: Dimeric analogs were synthesized and tested in binding, biochemical, and biological assays. RESULTS: One analog, 1-ss, binds TrkA with higher affinity than D3 and induces or stabilizes receptor dimers. However, 1-ss exhibited antagonistic activity, through two mechanisms. One mechanism is that 1-ss blocks NGF binding, unlike D3 which is non-competitive. Inhibition of NGF binding may be due to the linker of 1-ss filling the inter-receptor space that NGF traverses before docking. In a second mechanism, 1-ss acts as a pure antagonist, inhibiting NGF-independent TrkA activity in cells over-expressing receptors. Inhibition is likely due to 1-ss "freezing" the TrkA dimer in the inactive state. CONCLUSIONS: Dimerization of an RTK can result in antagonism, through two independent mechanisms. GENERAL SIGNIFICANCE: we report a small molecule monovalent agonist being converted to a bivalent antagonist.
BACKGROUND: Receptor tyrosine kinases (RTK) act through dimerization. Previously it was thought that only bivalent ligands could be agonistic, whereas monovalent ligands should be antagonistic. This notion changed after the demonstration that monovalent ligands can be agonistic, including our report of a small molecule monovalent ligand "D3" that is a partial agonist of the NGF receptor TrkA. A bivalent "D3-linker-D3" was expected to increase agonism. METHODS: Dimeric analogs were synthesized and tested in binding, biochemical, and biological assays. RESULTS: One analog, 1-ss, binds TrkA with higher affinity than D3 and induces or stabilizes receptor dimers. However, 1-ss exhibited antagonistic activity, through two mechanisms. One mechanism is that 1-ss blocks NGF binding, unlike D3 which is non-competitive. Inhibition of NGF binding may be due to the linker of 1-ss filling the inter-receptor space that NGF traverses before docking. In a second mechanism, 1-ss acts as a pure antagonist, inhibiting NGF-independent TrkA activity in cells over-expressing receptors. Inhibition is likely due to 1-ss "freezing" the TrkA dimer in the inactive state. CONCLUSIONS: Dimerization of an RTK can result in antagonism, through two independent mechanisms. GENERAL SIGNIFICANCE: we report a small molecule monovalent agonist being converted to a bivalent antagonist.
Authors: Martin A Bruno; Paul B S Clarke; Alicia Seltzer; Rémi Quirion; Kevin Burgess; A Claudio Cuello; H Uri Saragovi Journal: J Neurosci Date: 2004-09-15 Impact factor: 6.167
Authors: Fouad Brahimi; Alba Galan; Sean Jmaeff; Pablo F Barcelona; Nicolas De Jay; Kurt Dejgaard; Jason C Young; Claudia L Kleinman; David Y Thomas; H Uri Saragovi Journal: iScience Date: 2020-08-10
Authors: Fouad Brahimi; Mario Maira; Pablo F Barcelona; Alba Galan; Tahar Aboulkassim; Katrina Teske; Mary-Louise Rogers; Lisa Bertram; Jing Wang; Masoud Yousefi; Robert Rush; Marc Fabian; Neil Cashman; H Uri Saragovi Journal: PLoS One Date: 2016-10-03 Impact factor: 3.240
Authors: Andrew J Poole; Laura Frigotto; Matthew E Smith; Claudia Baar; Gabriela Ivanova-Berndt; Agnes Jaulent; Catherine Stace; Christopher G Ullman; Anna V Hine Journal: Sci Rep Date: 2019-01-30 Impact factor: 4.379