In vitro activity: Naftopidil is selective for the alpha1d-adrenoceptor with approximately 3- and 17-fold higher affinity than for the alpha1a- and alpha1b-adrenoceptor subtypes, respectively. Naftopidil has growth inhibitory effect in androgen-sensitive and -insensitive human prostate cancer cell lines. Naftopidil induces p21(cip1) but not p27(kip1) in PC-3 cells. Naftopidil induces apoptosis in all the investigated malignant mesothelioma cells, and a similar effect is obtained with prazosin, another α1-adrenoceptor blocker. Naftopidil-induced reduction in cell viability is inhibited by GF109203X, while prazosin-induced in cell viability is less affected. Naftopidil, an alpha 1-adrenoreceptor antagonist produces a concentration-dependent inhibition ofcollagen-induced Ca2+ mobilization, maximum inhibition (22.9%) occurring with 40 mM Naftopidil. Naftopidil also inhibits the adrenaline-induced rise in [Ca2+]i in a concentration-dependent manner (30 mM doxazosin), significant inhibitions of platelet aggregation also being produced. Naftopidil (0.3, 1, and 3 μM) inhibits 5-HT-induced bladder contraction in a concentration-dependent manner. Naftopidil inhibits both the 5-HT(2A) and 5-HT(2) receptor agonists-induced bladder contractions. Naftopidil binds to the human 5-HT(2A) and 5-HT(2B) receptors with pKi values of 6.55 and 7.82, respectively.

Jpn J Pharmacol. 1999 Apr;79(4):447-54; Eur J Pharmacol. 2013 Jan 30;700(1-3):194-200.