The synthetic cathinone psychostimulant alpha-PPP antagonizes serotonin 5-HT2A receptors

Abstract

Synthetic cathinones (SCs) are beta-keto analogs of amphetamines. Like amphetamines, SCs target monoamine transporters; however, unusual neuropsychiatric symptoms have been associated with abuse of some SCs, suggesting SCs might possess additional pharmacological properties. We performed radioligand competition binding assays to assess the affinities of nine SCs at human 5-HT2A receptors (5-HT2AR) and muscarinic M-1 receptors (M1R) transiently expressed in HEK293 cells. None of the SCs exhibited affinity at M1R (minimal displacement of [similar to K-d] [H-3]scopolamine up to 10 mu M). However, two SCs, alpha-pyrrolidinopropiophenone (alpha-PPP) and 4-methyl-alpha-PPP, had low mu M K-i values at 5-HT2AR. In 5-HT2AR-phosphoinositide hydrolysis assays, alpha-PPP and 4-methyl-alpha-PPP displayed inverse agonist activity. We further assessed the 5-HT2AR functional activity of alpha-PPP, and observed it competitively antagonized 5-HT2AR signaling stimulated by the 5-HT2R agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI; K-b = 851 nM). To assess in vivo 5-HT2AR activity, we examined the effects of alpha-PPP on the DOI-elicited head-twitch response (HTR) in mice. alpha-PPP dose-dependently blocked the HTR with maximal suppression at 10 mg/kg (P < 0.0001), which is a moderate dose used in studies investigating psychostimulant properties of alpha-PPP. To corroborate a 5-HT2AR mechanism, we also tested 3,4-methylenedioxy-alpha-PPP (MDPPP) and 3-bromomethcathinone (3-BMC), SCs that we observed had 5-HT2AR K(i)s > 10 mu M. Neither MDPPP nor 3-BMC, at 10 mg/kg doses, attenuated the DOI HTR. Our results suggest alpha-PPP has antagonist interactions at 5-HT2AR in vitro that may translate at physiologically-relevant doses in vivo. Considering 5-HT2AR antagonism has been shown to mitigate effects of psychostimulants, this property may contribute to alpha-PPPs unpopularity compared to other monoamine transporter inhibitors.