Cell Surface Notch Ligand DLL3 is a Therapeutic Target in Isocitrate Dehydrogenase-mutant Glioma.

Abstract

Isocitrate dehydrogenase (<i>IDH</i>)-mutant glioma is a distinct glioma molecular subtype for which no effective molecularly directed therapy exists. Low-grade gliomas, which are 80%-90% <i>IDH</i>-mutant, have high RNA levels of the cell surface Notch ligand DLL3. We sought to determine DLL3 expression by IHC in glioma molecular subtypes and the potential efficacy of an anti-DLL3 antibody-drug conjugate (ADC), rovalpituzumab tesirine (Rova-T), in <i>IDH</i>-mutant glioma. We evaluated <i>DLL3</i> expression by RNA using TCGA data and by IHC in a discovery set of 63 gliomas and 20 nontumor brain tissues and a validation set of 62 known <i>IDH</i> wild-type and mutant gliomas using a monoclonal anti-DLL3 antibody. Genotype was determined using a DNA methylation array classifier or by sequencing. The effect of Rova-T on patient-derived endogenous <i>IDH</i>-mutant glioma tumorspheres was determined by cell viability assay. Compared to <i>IDH</i> wild-type glioblastoma, <i>IDH</i>-mutant gliomas have significantly higher <i>DLL3</i> RNA (<i>P</i> < 1 × 10^-15) and protein by IHC (<i>P</i> = 0.0014 and <i>P</i> < 4.3 × 10^-6 in the discovery and validation set, respectively). DLL3 immunostaining was intense and homogeneous in <i>IDH</i>-mutant gliomas, retained in all recurrent tumors, and detected in only 1 of 20 nontumor brains. Patient-derived <i>IDH</i>-mutant glioma tumorspheres overexpressed DLL3 and were potently sensitive to Rova-T in an antigen-dependent manner. DLL3 is selectively and homogeneously expressed in <i>IDH</i>-mutant gliomas and can be targeted with Rova-T in patient-derived <i>IDH</i>-mutant glioma tumorspheres. Our findings are potentially immediately translatable and have implications for therapeutic strategies that exploit cell surface tumor-associated antigens.