Structure−Activity Relationships in 1,4-Benzodioxan-Related Compounds. 8. {2-[2-(4-Chlorobenzyloxy)phenoxy]ethyl}-[2-(2,6-dimethoxyphenoxy)ethyl]amine (Clopenphendioxan) as a Tool to Highlight the Involvement of α1D- and α1B-Adrenoreceptor Subtypes in the Regulation of Human PC-3 Prostate Cancer Cell Apoptosis and Proliferation

A series of new α1-adrenoreceptor antagonists (5−18) was prepared by introducing various substituents (Topliss approach) into the ortho, meta, and para positions of the benzyloxy function of the phendioxan open analogue 4 (“openphendioxan”). All the compounds synthesized were potent antagonists and generally displayed, similarly to 4, the highest affinity values at α1D- with respect to α1A- and α1B-AR subtypes and 5-HT1A subtype. By sulforhodamine B (SRB) assay on human PC-3 prostate cancer cells, the new compounds showed antitumor activity (estimated on the basis of three parameters GI50, TGI, LC50), at low micromolar concentration, with 7 (“clopenphendioxan”) exhibiting the highest efficacy. Moreover, this study highlighted for the first time α1D- and α1B-AR expression in PC3 cells and also demonstrated the involvement of these subtypes in the modulation of apoptosis and cell proliferation. A significant reduction of α1D- and α1B-AR expression in PC3 cells was associated with the apoptosis induced by 7....