Cell-free application of Deltex1 to suppress hyperactive notch signaling in t-cell acute lymphoblastic leukemia

Abstract T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy of immature T-cells. Aberrant activating mutations in Notch1 drive leukemia in the majority of T-ALL patients, and while treatments such as γ-secretase inhibitors and anti-Notch1 antibodies are available, they lack tissue specificity and are systemically toxic. By using an unbiased quantitative proteomic screen, we found that Deltex1 (Dtx1), an E3 Ubiquitin ligase is an interactor of the Transcriptional Activation Domain (TAD) of Notch1 and inhibits hyperactive signaling in a negative feedback loop. We show that Deltex proteins are inactivated and mutated in a portion of T-ALLs, promoting unchecked Notch1 signaling. Reintroduction of wildtype, full-length DTX1 in T-ALL cells inhibited cell growth by degrading the Notch1 receptor and suppressing hyperactive Notch signaling. To address tissue specificity, we developed targeted lipid nanoparticles to deliver wildtype Dtx1 protein to human T-ALL cells and primary murine leukemia in vivo. This treatment led to decreased growth and apoptosis of T-ALL cells in vitro, and abolished leukemia progression in vivo. Transcriptomic analysis revealed a significant decrease in Notch pathway activity and in cell cycle progression of T-ALL that receive nanoparticle treatment. Furthermore, the nanoparticle treatment synergized with existing standard-of-care chemotherapy such as Nelarabine, indicating a novel clinically relevant approach for treating refractory T-ALL.