Pharmacological characterization of a novel investigational antimuscarinic drug, fesoterodine, in vitro and in vivo

Abstract

OBJECTIVE To investigate the primary pharmacology of fesoterodine (a novel antimuscarinic drug developed for treating overactive bladder) and SPM 7605 (its active metabolite, considered to be the main pharmacologically active principle of fesoterodine in man) against human muscarinic receptor subtypes, and to investigate in vitro and in vivo functional activity of these agents on the rat bladder compared with existing standard agents. MATERIALS AND METHODS The displacement of radioligand binding by fesoterodine, SPM 7605 and standard agents in membrane preparations of Chinese hamster ovary (CHO) cells expressing the different human muscarinic receptors (M1–M5) was characterized. Agonistic and antagonistic activities were studied using different CHO cell lines stably expressing the human recombinant muscarinic receptor subtypes. The effects of fesoterodine and SPM 7605 on isolated bladder strips contracted by carbachol or electrical field stimulation (EFS) were investigated. In vivo the effects of fesoterodine and SPM 7605 on micturition variables were assessed using continuous cystometry in conscious female Sprague‐Dawley rats, and compared to those of oxybutynin and atropine. RESULTS In vitro SPM 7605 potently inhibited radioligand binding at all five human muscarinic receptor subtypes with equal affinity across all five. Fesoterodine had a similar balanced selectivity profile but was less potent than SPM 7605. Both substances were competitive antagonists of cholinergic agonist‐stimulated responses in human M1‐M5 cell lines and had a similar potency and selectivity profile to the radioligand‐binding studies. In rat bladder strips, fesoterodine and SPM 7605 caused a rightward shift of the concentration‐response curve for carbachol with no depression of the maximum, and concentration‐dependently reduced contractions induced by EFS. The potency of both drugs was similar to that of atropine and oxybutynin. In the presence of the esterase inhibitor neostigmine, the concentration‐response curve of fesoterodine was shifted to the right, suggesting that part of the activity was caused by metabolism to SPM 7605 by tissue enzymes. In vivo, low doses (0.01 mg/kg) of fesoterodine and SPM 7605 reduced micturition pressure and increased intercontraction intervals and bladder capacity, but did not affect residual volume. CONCLUSIONS Fesoterodine and its active metabolite, SPM 7605, are nonsubtype selective, competitive antagonists of human muscarinic receptors, but SPM 7605 has greater potency than the parent compound. Pharmacodynamic studies in the rat bladder in vitro confirm the competitive muscarinic antagonist profile of these agents in a native tissue preparation, and in vivo studies in the rat showed effects on bladder function consistent with a muscarinic antagonist profile.

Enhanced Sensitivity to Afferent Stimulation and Impact of Overactive Bladder Therapies in the Conscious, Spontaneously Hypertensive Rat

“…The ability of muscarinic antagonism to reduce MP in multiple species, including rats, is well documented (Angelico et al, 2005;Ney et al, 2008;McCafferty et al, 2009). Likewise, MI shortening and VV reduction in the SHR in response to muscarinic antagonism is consistent with previous rat studies (Igawa et al, 1993;Takeda et al, 2000Takeda et al, , 2002Ney et al, 2008). Overall, our urodynamic observations in response to muscarinic antagonism in the SHR are consistent with previous findings in cystometric studies of normal rats.…”

“…The deleterious effects on SHR functional bladder capacity do not reflect an effect of overdosing, because considerably lower doses (10-to 30-fold) of both oxybutynin or darifenacin did not provide an enhancement of VV or MI. The ability of muscarinic antagonism to reduce MP in multiple species, including rats, is well documented (Angelico et al, 2005;Ney et al, 2008;McCafferty et al, 2009). Likewise, MI shortening and VV reduction in the SHR in response to muscarinic antagonism is consistent with previous rat studies (Igawa et al, 1993;Takeda et al, 2000Takeda et al, , 2002Ney et al, 2008).…”

Comparison of Receptor Binding Characteristics of Commonly Used Muscarinic Antagonists in Human Bladder Detrusor and Mucosa

“…Table 2 shows the two-site binding analysis for fesoterodine to detrusor and mucosal membranes. Our pK i values at the low-affinity binding sites in detrusor and mucosal membranes (7.68 and 7.87, respectively) correspond well with the pK i value reported by Ney et al (2008) for fesoterodine at the M 2 receptor (pK i , 7.7). Furthermore, our pK i values for the high-affinity binding site in detrusor and mucosa membranes (8.78 and 9.95, respectively) correspond well with the pK i value reported by Ney et al (2008) for SPM7605 binding to M 2 receptors (pK i , 9.2).…”

“…Fesoterodine two-site binding data were compared with the data from Ney et al (2008) for fesoterodine and SPM7605 (Table 2). The pK i values for the "high-affinity site" in M 1 to M 5 CHO cell membranes seemed to correspond closely to the pK i values reported for SPM7605 at M 1 to M 5 receptor subtypes, whereas the pK i values at the "low-affinity binding site" in M 1 to M 5 CHO cell corresponded closely to pK i values reported for fesoterodine binding to M 1 to M 5 receptor subtypes (Table 2).…”

“…The agents examined were darifenacin and its hydroxylated metabolite UK-148,993, fesoterodine, solifenacin, tolterodine, and trospium. Fesoterodine is a prodrug in that it is rapidly metabolized by nonspecific tissue and plasma esterases to produce the more active metabolite SPM7605 (Ney et al, 2008).…”