Abstract
Antibody-drug conjugates (ADCs) combining monoclonal antibodies with cytotoxic payloads are a rapidly emerging class of immune-based therapeutics with the potential to improve the treatment of cancer, including children with relapse/refractory acute lymphoblastic leukemia (ALL). CD123, the α subunit of the interleukin-3 receptor, is overexpressed in ALL and is a potential therapeutic target. Here, we show that pivekimab sunirine (PVEK), a recently developed ADC comprising the CD123-targeting antibody, G4723A, and the cytotoxic payload, DGN549, was highly effective in vivo against a large panel of pediatric ALL patient-derived xenograft (PDX) models (n = 39). PVEK administered once weekly for 3 weeks resulted in a median event-free survival (EFS) of 57.2 days across all PDXs. CD123 mRNA and protein expression was significantly higher in B-lineage (n = 65) compared with T-lineage (n = 25) ALL PDXs (p < 0.0001), and mice engrafted with B-lineage PDXs achieved significantly longer EFS than those engrafted with T-lineage PDXs (p < 0.0001). PVEK treatment also resulted in significant clearance of human leukemia cells in hematolymphoid organs in mice engrafted with B-ALL PDXs. Notably, our results showed no direct correlation between CD123 expression and mouse EFS, indicating that CD123 is necessary but not sufficient for in vivo PVEK activity. Importantly, a PDX with very high CD123 cell surface expression but resistant to in vivo PVEK treatment, failed to internalize the G4723A antibody while remaining sensitive to the PVEK payload, DGN549, suggesting a novel mechanism of resistance. In conclusion, PVEK was highly effective against a large panel of B-ALL PDXs supporting its clinical translation for B-lineage pediatric ALL.