Targeting Translation Control with p70 S6 Kinase I Inhibitors to Reverse Phenotypes in Fragile X Syndrome Mice

Aberrant neuronal translation is implicated in the etiology of numerous brain disorders. Although mTORCI-p70 ribosomal S6 kinase I (S6KI) signaling is critical for translational control, pharmacological manipulation in vivo has targeted exclusively 'mTORCI due to the paucity of specific inhibitors to S6KI. However, small molecule inhibitors of S6KI could potentially ameliorate pathological phenotypes of diseases, which are based on aberrant translation and protein expression. One such condition is fragile X syndrome (FXS), which is considered to be caused by exaggerated neuronal translation and is the most frequent heritable cause of autism spectrum disorder (ASD). To date, potential therapeutic interventions in FXS have focused largely on targets upstream of translational control to normalize FXS-related phenotypes. Here we test the ability of two S6KI inhibitors, PF-4708671 and FS-115, to normalize translational homeostasis and other phenotypes exhibited by FXS model mice. We found that although the pharmacokinetic profiles of the two S6K1 inhibitors differed, they overlapped in reversing multiple disease-associated phenotypes in FXS model mice including exaggerated protein synthesis, inappropriate social behavior, behavioral inflexibility, altered dendntic spine morphology, and macroorchidism. In contrast, the two inhibitors differed in their ability to rescue stereotypic marble-burying behavior and weight gain. These findings provide an initial pharmacological characterization of the impact of S6KI inhibitors in vivo for FXS, and have therapeutic implications for other neuropsychiatric conditions involving aberrant mTORC I-S6KI signaling.