Single-ChainNanobody Inhibition of Notch and AvidityEnhancement Utilizing the β‑Pore-Forming Toxin Aerolysin

Notch plays critical roles in developmental processes and disease pathogenesis, which have led to numerous efforts to modulate its function with small molecules and antibodies. Here we present a nanobody inhibitor of Notch signaling derived from a synthetic phage-display library targeting the Notch negative regulatory region (NRR). The nanobody inhibits Notch signaling in a luciferase reporter assay with an IC₅₀ of about 5 μM and in a Notch-dependent hematopoietic progenitor cell differentiation assay, despite a modest 19 μM affinity for the Notch NRR. We addressed the low affinity by fusion to a mutant varient of the β-pore-forming toxin aerolysin, resulting in a significantly improved IC₅₀ for Notch inhibition. The nanobody-aerolysin fusion inhibits proliferation of T-ALL cell lines with efficacy similar to that of other Notch pathway inhibitors. Overall, this study reports the development of a Notch inhibitory antibody and demonstrates a proof-of-concept for a generalizable strategy to increase the efficacy and potency of low-affinity antibody binders.