Targeting DDX3X to develop new effective therapeutic approaches against DDX3X syndrome and glioblastoma.

DEAD – box helicase 3 (DDX3X) is a widely studied member of the DEAD – box RNA helicase subfamily, reported to take part in different steps of RNA metabolism, including transcription, splicing, nuclear export and translation. In addition to its helicase activity DDX3X shows ribonuclease activity, and it is the only enzyme besides RNase – H2 capable of taking part into Ribonucleotide Excision Repair (RER) pathway. DDX3X is considered a valuable therapeutic target since it is involved in cancer progression: this protein displays a dual role, acting as an oncogene or as a tumor suppressor according to each tumor type. In fact, DDX3X hampers both Wnt and Snail pathways, crucial in regulation of cell cycle progression. Moreover, DDX3X is involved in the replication of several viruses, showing either anti – viral or pro – viral activities. Furthermore, de novo germline mutations of DDX3X account for 1% - 3% of intellectual disabilities in children, causing the so – called DDX3X syndrome, a neurodevelopmental disorder. In this thesis project wild type DDX3X and R376C DDX3X were purified: the R376C mutation is found in DDX3X syndrome female patients. These proteins were biochemically characterized for their helicase and ribonuclease activities as single enzymes and in synergy, in order to shed light on the catalytic impairment of DDX3X in DDX3X syndrome patients presenting this mutation either in homo or in heterozygosis. These results will be coupled with in vivo studies carried on by our collaborators at Mount Sinai University (New York), with the aim of getting a deeper insight into the molecular pathogenesis of this disease. Moreover, our collaborators from Lead Discovery Siena designed inhibitory compounds targeting the RNA – binding pocket of DDX3X. In this work, their inhibitory power and selectivity against DDX3X are tested, and promising results come from both in vitro and in vivo experiments: one of these compounds, compound 11, is able to inhibit proliferation of glioblastoma multiforme in mice. In conclusion, results from this thesis work underline the possibility of exploiting DDX3X as a therapeutic target for glioblastoma multiforme, a brain tumor for which no treatment is currently available, as well as for DDX3X syndrome.