The anti-overactive bladder activity of KW-7158 is mediated by blocking equilibrative nucleoside transporter-1

KW-7158 is a novel therapeutic candidate for treating overactive bladder (OAB) with a unique mode of action: suppression of sensory afferent nerves. However, the molecular target of this compound remains unknown. We herein report the identification of the KW-7158 target to be equilibrative nucleoside transporter-1 (ENT1). A membrane protein expression library of ca. 7000 genes was expressed in a dorsal root ganglion cell line, which we had previously generated, and subjected to screening for binding with a fluorescent derivative that retains high binding activity to the target. The screening revealed that only cells transfected with an ENT1 expression vector exhibited significant binding. We next performed [(3)H]KW-7158 binding experiments and an adenosine influx assay and found that KW-7158 binds to and inhibits ENT1. To further demonstrate the pharmacological relevance, we evaluated other known ENT1 inhibitors (nitrobenzylthioinosine, dipyridamole, draflazine) in an in vitro bladder strip contraction assay and the rat spinal cord injury OAB model. We found that all of the inhibitors exhibited anti-OAB activities, of which the potencies were comparable to that of adenosine influx inhibition in vitro. These studies demonstrated that the pharmacological target of KW-7158 is ENT1, at least in the rat OAB model. Our results will aid understanding of the precise mechanism of action of this drug and may also shed new light on the use of the adenosine pathway for the treatment of OAB.