Novel Bivalent 5-HT2A Receptor Antagonists Exhibit High Affinity and Potency in Vitro and Efficacy in Vivo.

The 5-HT2A receptor (5-HT2AR) plays an important role in various neuropsychiatric disorders, including substance use disorder and schizophrenia. Homodimerization of this receptor has been suggested, but tools that allow direct assessment of the relevance of the 5-HT2AR:5-HT2AR homodimer in these disorders are necessary. We chemically modified the selective 5-HT2AR antagonist M100907 to synthesize a series of homobivalent ligands connected by ethylene glycol linkers of varying lengths that may be useful tools for probing 5-HT2AR:5-HT2AR homodimer function. We tested these molecules for 5-HT2AR antagonist activity in a cell line stably expressing the functional 5-HT2AR and quantified a downstream signaling target, activation (phosphorylation) of extracellular regulated kinases 1/2 (ERK1/2), in comparison to in vivo efficacy of altering spontaneous or cocaine-evoked locomotor activity in rats. All of the synthetic compounds inhibited 5-HT-mediated phosphorylation of ERK1/2 in the cellular signaling assay; the potency of the bivalent ligands varied as a function of linker length, with the intermediate linker lengths being the most potent. The Ki values for the binding of bivalent ligands to 5-HT2AR were only slightly lower than the values for the parent (+)-M100907 compound, but significant selectivity for 5-HT2AR over 5-HT2BR or 5-HT2CR binding was retained. In addition, the 11-atom-linked bivalent 5-HT2AR antagonist (2 mg/kg, intraperitoneally) demonstrated efficacy on par with that of (+)-M100907 in inhibiting cocaine-evoked hyperactivity. As we develop further strategies for ligand-evoked receptor assembly and analyses of diverse signaling and functional roles, these novel homobivalent 5-HT2AR antagonist ligands will serve as useful in vitro and in vivo probes of 5-HT2AR structure and function.