Receptor signaling and behavioral properties of EFF0311, a longer‐acting selective full D1 agonist as a potential treatment for Parkinson's disease

Abstract

D1 dopamine full agonists like dihydrexidine (DHX) were previously used to show that D1, but not D2, agonists could match the efficacy of levodopa in the primate MPTP Parkinson's disease (PD) model and in humans with PD. Short duration of action, toxicity, and/or limited bioavailability have prevented a D1 agonist from being approved for clinical use, with only DHX (very short acting) available for limited investigator‐initiated clinical studies. We now report the properties of EFF0311, a DHX analog with greater D1 selectivity and nanomolar affinity for D1 and D5 receptors. EFF0311 had 100% intrinsic activity in stimulating adenylate cyclase via D1 receptors in expressed systems or brain. EFF0311 (relative to quinpirole) was far less potent at D2L‐mediated stimulation of arachidonic acid release than in inhibition of forskolin‐stimulated adenylate cyclase, consistent with functionally selective actions at D2L receptors. In the unilateral 6‐OHDA rat model of PD, EFF0311 effects lasted 3–5 times longer than DHX. These behavioral effects were completely blocked by a D1 antagonist, but not decreased by a D2 antagonist. The properties of EFF0311 (D1 full agonism, longer duration of action, atypical D2 actions) suggest it may be an ideal PD drug candidate.Grant support: MH082441, MH040537, PA Keystone Innovation Grant (RBM), NS042402 and PA Tobacco settlement fund (TS). RBM has a potential CoI.