Discovery of the First Potent, Selective, and Orally Bioavailable Signal Peptide Peptidase-Like 2a (SPPL2a) Inhibitor Displaying Pronounced Immunomodulatory Effects In Vivo

Signal peptide peptidase-like 2a (SPPL2a) is an aspartic intramembrane protease which has recently been shown to play an important role in the development and function of antigen presenting cells such as B lymphocytes and dendritic cells. In this paper, we describe the discovery of the first selective and orally active SPPL2a inhibitor (<i>S</i>)-2-cyclopropyl-<i>N</i>1-((<i>S</i>)-5,11-dioxo-10,11-dihydro-1<i>H</i>,3<i>H</i>,5<i>H</i>-spiro­[benzo­[<i>d</i>]­pyrazolo­[1,2-<i>a</i>]­[1,2]­diazepine-2,1′-cyclopropan]-10-yl)-<i>N</i>4-(5-fluoro-2-methylpyridin-3-yl)­succinamide <b>40</b> (<b>SPL-707</b>). This compound shows adequate selectivity against the closely related enzymes γ-secretase and SPP and a good pharmacokinetic profile in mouse and rat. Compound <b>40</b> significantly inhibited processing of the SPPL2a substrate CD74/p8 fragment in rodents at doses ≤10 mg/kg b.i.d. po. Oral dosing of <b>40</b> for 11 days at ≥10 mg/kg b.i.d. recapitulated the phenotype seen in Sppl2a knockout (ko) and ENU mutant mice (reduced number of specific B cells and myeloid dendritic cells). Thus, we believe that SPPL2a represents an interesting and druggable pharmacological target, potentially providing a novel approach for the treatment of autoimmune diseases by targeting B cells and dendritic cells