Abstract:
G-protein coupled receptors (GPCRs) such as the vasopressin-2 receptor
(V2R) are an important class of drug targets. An efficient high-throughput screening
assay was developed for GPCR-induced cAMP elevation using as read-out cAMP
activation of cystic fibrosis transmembrane conductance regulator (CFTR) Clchannels.
Fischer rat thyroid cells expressing CFTR and a halide-sensing yellow
fluorescent protein (YFP-H148Q/I152L) were transfected with V2R. Increased cell
Cl- conductance following agonist-induced cAMP elevation was assayed using a
platereader from the cell fluorescence following solution I- addition. The Z-factor
for the assay was ~0.7 with the V2R agonist dDAVP (1 nM) as positive control.
Primary screening of 50,000 small molecules yielded novel classes of 5-aryl-4-
benzoyl-3-hydroxy-1-(2-arylethyl)-2H-pyrrol-2-one (V2Rinh class), a V2R
antagonist, and 2-(acylamino)-3-thiophenecarboxylates (PDEact class), a possible
phosphodiesterase activator. The most potent compounds in the V2Rinh class,
V2Rinh-02, fully displaced the radiolabeled vasopressin in binding experiments with
the IC50 of ~70 nM. Through reduction of the cAMP level, the PDEact inhibited not
only the dDAVP-, but also cholera toxin-, forskolin-, and dibutylryl cAMP-induced
transepithelial currents. Therefore, activation of phosphodiesterase was a suggested
mechanism action. The in vitro properties of the V2Rinh and PDEact suggested their
potential utility in aquaretic applications, and in conditions with pathologic
elevation of cyclic nucleotide levels, respectively.