Evaluation of the DLL3-targeting antibody-drug conjugate rovalpituzumab tesirine in preclinical models of neuroblastoma

Abstract Neuroblastomas have neuroendocrine features and often show similar gene expression patterns to small cell lung cancer including high expression of delta-like ligand 3 (DLL3). We determine the efficacy of rovalpituzumab tesirine (Rova-T), an antibody drug conjugated with a pyrrolobenzodiazepine dimer toxin targeting DLL3, in preclinical models of human neuroblastoma. We evaluated DLL3 expression in RNA sequencing data sets and performed immunohistochemistry on neuroblastoma patient derived xenograft, human neuroblastoma primary tumor and normal childhood tissue microarrays. We then evaluated the activity of Rova-T against 11 neuroblastoma PDX models using varying doses and schedules and compared anti-tumor activity to expression levels. DLL3 mRNA was differentially overexpressed in neuroblastoma at comparable levels to small cell lung cancer, as well as Wilms and rhabdoid tumors. DLL3 protein was robustly expressed across the neuroblastoma PDX array, but membranous staining was variable. The human neuroblastoma array, however, showed staining in only 44% of cases, whereas no significant staining was observed in the normal childhood tissue array. Rova-T showed a clear dose response effect across models tested, with a single dose inducing a complete or partial response in 3/11 and stable disease in another 3/11 models. No signs of toxicity were observed, and no treatment-related mortality. Strong membranous staining was necessary, but not sufficient, for anti-tumor activity. Rova-T has activity in a subset of neuroblastoma preclinical models, but heterogeneous expression and the near absence of expression seen in human tumors suggests that any DLL3-targeting clinical trial should be performed with a robust companion diagnostic for patient selection.