Is the anti-psychotic, 10-(3-(dimethylamino)propyl)phenothiazine (promazine), a potential drug with which to treat SARS infections? Lack of efficacy of promazine on SARS-CoV replication in a mouse model

Phenothiazine and derivatives were tested for inhibition of SARS-CoV replication. Phenothiazine slightly inhibited SARS-CoV replication in a neutral red (NR) uptake assay. Adding a propylamino group to give promazine reduced virus yields (VYR assay) with an EC90 = 8.3 +/- 2.8 mu M, but without selectivity. Various substitutions in the basic phenothiazine structure did not promote efficacy. Phenazine ethosulfate was the most potent compound by VYR assay (EC90 = 6.1 +/- 4.3 mu M). All compounds were toxic (IC50 = 6.6-74.5 mu M) except for phenoxathiin (IC50 = 858 +/- 208 mu M) and 10-(alpha-diethylaniino-propionyl) phenothiazine center dot HCl (IC50 = 195 +/- 71.2 mu M). Consequently, none were selective inhibitors of SARS-CoV replication (SI values <1-3.3 mu M). These data portended the poor efficacy of promazine in a SARS-CoV mouse lung replication model. Intraperitoneal treatment with promazine using a prophylactic (-4 h)/therapeutic regimen of 1, 10, or 50 mg/(kg day) did not reduce virus lung titers at day 3, yet prolonged virus replication to 14 days. Similar therapeutic promazine doses were not efficacious. Thus, promazine did not affect SARS-CoV replication in vitro or in vivo, nor were any other phenothiazines efficacious in reducing virus replication. Therefore, treating SARS infections with compounds like promazine is not warranted. (C) 2008 Published by Elsevier B.V.