Phenylarsine oxide inhibits ex vivo HIV-1 expression. 
Phenylarsine oxide (PAO), which is described as an inhibitor of tyrosine phosphatase activity, inhibits H2O2 release from human peripheral blood mononuclear cells (PBMCs) as measured by electrochemistry. Since human immunodeficiency virus type 1 (HIV-1) replication is known to be favored under oxidative stress conditions, ex vivo experiments using uninfected PBMCs, primary monocytes or a latently infected promonocytic U1 cell line show that HIV-1 replication and reactivation, monitored by p24 antigen measurement, are inhibited by PAO in a time- and concentration-dependent manner. These observations can be linked with the inhibition of NF-kappa B activation when uninfected monocytes are induced by either tumor necrosis factor alpha (TNF-alpha) phorbol 12-myristate 13-acetate (PMA) or lipopolysaccharide (LPS).