Parallel functional activity profiling reveals valvulopathogens are potent 5-hydroxytryptamine_2B receptor agonists: Implications for drug safety assessment

Drug-induced valvular heart disease (VHD) is a serious side effect of a few medications, including some that are on the market. Pharmacological studies of VHD-associated medications (e.g., fenfluramine, pergolide, methysergide, and cabergoline) have revealed that they and/or their metabolites are potent 5-hydroxytryptamine_2B (5-HT_2B) receptor agonists. We have shown that activation of 5-HT_2B receptors on human heart valve interstitial cells in vitro induces a proliferative response reminiscent of the fibrosis that typifies VHD. To identify current or future drugs that might induce VHD, we screened approximately 2200 U.S. Food and Drug Administration (FDA)-approved or investigational medications to identify 5-HT_2B receptor agonists, using calcium-based high-throughput screening. Of these 2200 compounds, 27 were 5-HT_2B receptor agonists (hits); 14 of these had previously been identified as 5-HT_2B receptor agonists, including seven bona fide valvulopathogens. Six of the hits (guanfacine, quinidine, xylometazoline, oxymetazoline, fenoldopam, and ropinirole) are approved medications. Twenty-three of the hits were then "functionally profiled" (i.e., assayed in parallel for 5-HT_2B receptor agonism using multiple readouts to test for functional selectivity). In these assays, the known valvulopathogens were efficacious at concentrations as low as 30 nM, whereas the other compounds were less so. Hierarchical clustering analysis of the pEC₅₀ data revealed that ropinirole (which is not associated with valvulopathy) was clearly segregated from known valvulopathogens. Taken together, our data demonstrate that patterns of 5-HT_2B receptor functional selectivity might be useful for identifying compounds likely to induce valvular heart disease.