A Novel DLL1-Anti-CD19 Chimeric Protein Effectively Targets Notch Activation to B-Cell Acute Lymphoblastic Leukemia and Induces Cell Death

Background: Acute lymphoblastic leukemia (ALL) is the most prevalent form of cancer in children, and those who relapse continue to have poor survival. Therefore, the development of improved and specifically targeted treatment options is vital. The Notch pathway has been shown to act as a tumor suppressor in B-ALL via cell type specific induction of growth-inhibiting and pro-apoptotic pathways. In this study, we aim to therapeutically activate Notch signaling in B-ALL via targeting the Notch ligand DLL1 to B cells using an anti-CD19 scFv chimeric protein.

Methods: A soluble chimeric protein composed of the extracellular domain of the Notch ligand DLL1 linked to a validated anti-CD19 scFv was isolated from HEK-293 producer cells. Human B-ALL (SB, Nalm6) and T-ALL (Jurkat) lines were treated with DLL1-anti-CD19scFv chimeric protein, and expression of the Notch target gene HES1 and effects on cell growth and survival were measured.

Results: Both B- and T-ALL lines express Notch1 and Notch2 receptors on the cell surface. Exposure of B-ALL cells to DLL1-anti-CD19scFv chimeric protein led to an increase of Notch signaling, measured via 3-14 fold increase in HES1 mRNA expression. As expected, surface expression of the Notch receptors decreased upon chimera exposure, as Notch receptors are cleaved and destroyed upon activation. Importantly, exposure of the B-ALL lines to the chimeric protein led to a maximum 60% decrease in cell counts over 3-4 days, in contrast to T-ALL, where exposure did not effect growth significantly.

Conclusions: This study demonstrates that Notch signaling can be feasibly activated in human B-ALL cells through a soluble DLL1-anti-CD19 scFv chimeric protein. Activation of Notch signaling via this method leads to growth inhibition and cell death in B-ALL, but not T-ALL cells. Based on our findings, we suggest that this soluble DLL1-anti-CD19 chimera may be a potential therapeutic approach for B-ALL, and further in vivo testing is warranted.