Evaluation of the DLL3-targeting Antibody–Drug Conjugate Rovalpituzumab Tesirine in Preclinical Models of Neuroblastoma

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). Here we determine the efficacy of rovalpituzumab tesirine (Rova-T), an antibody–drug conjugated (ADC) with a pyrrolobenzodiazepine dimer toxin targeting DLL3, in preclinical models of human neuroblastoma. We evaluated DLL3 expression in RNA-sequencing datasets and performed IHC on neuroblastoma patient-derived xenograft (PDX), 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 antitumor activity with 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 the 11 models tested, with a single dose inducing a complete or partial response in 3 of 11 and stable disease in another 3 of 11 models. No overt signs of toxicity were observed, and there was no treatment-related mortality. Strong membranous staining was necessary, but not sufficient, for antitumor activity. Rova-T has activity in a subset of neuroblastoma preclinical models, but heterogeneous expression in these models and the near absence of expression seen in human tumors suggests that any DLL3-targeting clinical trial should be only performed with a robust companion diagnostic to evaluate DLL3 expression for patient selection. SIGNIFICANCE: GD2-directed antibody therapy is standard of care for high-risk neuroblastoma; therapy is toxic, and relapses often occur. DLL3, an inhibitory Notch ligand, is overexpressed in several neuronal cancers. A DLL3-targeting ADC showed objective activity only in neuroblastoma models with high DLL3 expression. These data provide vigilance about clinical development of DLL3 immunotherapies for neuroblastoma.