Andrea Cerase, PhD - "Reactivating the inactive X chromosome by small molecule screening as a treatment for X-linked disorders"

Andrea Cerase, PhD

Rett syndrome (RTT) and CDKL5 deficiency (CDD) syndromes are two severe neurodevelopmental disorders caused by mutations in the X-linked genes MeCP2 and Cdkl5, respectively. While MeCP2 mutations are lethal in most males, females survive birth but show severe neurological defects. Similarly, CDD shows a highly skewed 12:1 female-to-male ratio. 
Females silence one of the two X chromosomes at random in a process called X-chromosome inactivation (XCI). Approximately 50% of the cells silence the wild-type (WT) copy of the MeCP2/Cdkl5 genes. Thus, reactivating the silent WT copy of MeCP2/Cdkl5 could provide therapeutic intervention for RTT and CDD. Toward this goal, we screened ~ 28,000 small-molecule compounds from several libraries using a MeCP2-luciferase reporter cell line and cortical neurons from a MeCP2-EGFP mouse model. We used the gain/increase of luminescence or fluorescence as a readout of MeCP2 reactivation and tested the efficacy of these drugs under different drug regimens, conditions, and cellular contexts. We identified the JAK/STAT pathway inhibitors as XCI-reactivating agents, both by in vitro and ex vivo assays. In particular, we showed that AG-490, a Janus Kinase 2 (JAK2) kinase inhibitor, and Jaki, a pan JAK/STAT inhibitor, can reactivate MeCP2 from the inactive X chromosome in different cellular contexts. Recently we set up a second-generation double-reporter screening system to screen for the reactivation of MeCP2 and Cdkl5 genes, using dedicated peptidomimetic libraries. We will present preliminary results from this screen.