Revisiting the Pharmacodynamic Uroselectivity of α1-Adrenergic Receptor Antagonists

alpha(1)-Adrenoceptor (AR) antagonists are widely used for the relief of urinary retention secondary to benign prostatic hyperplasia (BPH). While the five Food and Drug Administration-approved alpha(1)-AR antagonists (terazosin, doxazosin, alfuzosin, tamsulosin, and silodosin) share similar efficacy, they differ in tolerability, with reports of ejaculatory dysfunction. The aim of the present work was to revisit their alpha(1)-AR subtype selectivity as well as of LDT5 (1-(2-nnethoxyphenyl)-4-[2-(3,4-dimethox-yphenyl) ethyl]piperazine nnonohydrochloride), a compound previously described as a multitarget antagonist of alpha 1A(-)/alpha 1D(-)AR and 5-HT1A receptors, and to estimate their affinity for D-2, D-3, and 5-HT1A receptors, which are putatively involved in ejaculatory dysfunction. Competition binding assays were performed with native (D-2, 5-HT1A) or transfected (human alpha(1A)-, alpha(1B-,) a alpha(1Dt)-AR, and D-3) receptors for determination of the drug's affinities. Tamsulosin and silodosin have the highest affinities for alpha(1A)-AR, but only silodosin is clearly a selective alpha(1A)-AR antagonist, with K, ratios of 25.3 and 50.2 for the alpha(1D)- and alpha(1B)-AR, respectively. Tamsulosin, silodosin, and LDT5 (but not terazosin, doxazosin, and alfuzosin) have high affinity for the 5-HT1A receptor (K-i around 5-10 nM), behaving as antagonists. We conclude that the uroselectivity of tamsulosin is not explained by its too-low selectivity for the alpha(1A)- versus alpha(1B)-AR, and that its affinity for D-2 and D-3 receptors is probably too low for explaining the ejaculatory dysfunction reported for this drug. Present data also support the design of "better-than-LDT5" new multitarget lead compounds with pharmacokinetic selectivity based on poor brain penetration and that could prevent hyperplastic cell proliferation and BPH progression. SIGNIFICANCE STATEMENT The present work revisits the uroselectivity of the five Food and Drug Administration-approved alpha(1) adrenoceptor antagonists for the treatment of benign prostatic hyperplasia (BPH). Contrary to what has been claimed by some, our results indicate that the uroselectivity of tamsulosin is probably not fully explained by its too-weak selectivity for the alpha(1A) versus alpha(1B) adrenoceptors. We also show that tamsulosin affinity for D-3 and 5-HT1A receptors is probably too low for explaining the ejaculatory dysfunction reported for this drug. Based on our lead compound LDT5, present data support the search for a multitarget antagonist of alpha(1A)-alpha(1D) and 5-HT1A receptors with poor brain penetration as an alternative for BPH treatment.