Muscarinic M3 positive allosteric modulator ASP8302 enhances bladder contraction and improves voiding dysfunction in rats.

Objectives: Muscarinic M₃ (M₃ ) receptors mediate cholinergic smooth muscle contraction of the bladder. Current drugs targeting bladder M₃ receptors for micturition disorders have a risk of cholinergic side effects due to excessive receptor activation and insufficient selectivity. We investigated the effect of ASP8302, a novel positive allosteric modulator (PAM) of M₃ receptors, on bladder function in rats.

Methods: Modulation of carbachol-induced increases in intracellular Ca²⁺ was assessed in cells expressing rat muscarinic receptors. Potentiation of bladder contractions was evaluated using isolated rat bladder strips and by measuring intravesical pressure in anesthetized rats. Conscious cystometry was performed to investigate the effects on residual urine volume and voiding efficiency in rat voiding dysfunction models induced by the α₁ -adrenoceptor agonist midodrine and muscarinic receptor antagonist atropine, and bladder outlet obstruction. To assess potential side effects, the number of stools and tracheal insufflation pressure were measured in conscious and anesthetized rats, respectively.

Results: ASP8302 demonstrated PAM effects on the rat M₃ receptor in cell assays, and augmented cholinergic bladder contractions both in vivo and in vitro. ASP8302 improved voiding efficiency and reduced residual urine volume in two voiding dysfunction models as effectively as distigmine bromide, but unlike distigmine bromide did not affect the number of stools or tracheal insufflation pressure.

Conclusions: Our results in rats indicate that ASP8302 improves voiding dysfunction by potentiating bladder contraction with fewer effects on cholinergic responses in other organs, and suggest a potential advantage over current cholinomimetic drugs for treating micturition disorders caused by insufficient bladder contraction.