Targeting axonal guidance dependencies in glioblastoma with ROBO1 CAR T cells
Resistance to genotoxic therapies and tumor recurrence are hallmarks of glioblastoma (GBM), an aggressive brain tumor. Here, we explore functional drivers of post-treatment recurrent GBM. By conducting genome-wide CRISPR-Cas9 knockout screens in patient-derived GBM models, we uncover distinct genetic dependencies in recurrent tumor cells absent in their patient-matched primary predecessors, accompanied by increased mutational burden and differential transcript and protein expression. These analyses map a multilayered genetic response to drive tumor recurrence, identifying protein tyrosine phosphatase 4A2 (PTP4A2) as a novel modulator of self-renewal, proliferation and tumorigenicity at GBM recurrence. Genetic perturbation or small molecule inhibition of PTP4A2 activity represses axon guidance activity through a dephosphorylation axis with roundabout guidance receptor 1 (ROBO1), exploiting a functional dependency on ROBO signaling. Importantly, engineered anti-ROBO1 single-domain antibodies mimic effects of PTP4A2 inhibition. Since a pan-PTP4A inhibitor was limited by poor penetrance across the blood brain barrier (BBB) in vivo, a second-generation chimeric antigen receptor (CAR)-T cell therapy was engineered against ROBO1 that elicits specific and potent anti-tumor responses in vivo. A single dose of anti-ROBO1 CAR-T cells doubles median survival in patient-derived xenograft (PDX) models of recurrent glioblastoma, and also eradicates tumors in ~50% of mice in PDX models of adult lung-to-brain metastases and pediatric relapsed medulloblastoma. We conclude that functional reprogramming drives tumorigenicity and dependence on a multi-targetable PTP4A-ROBO1 signaling axis at GBM recurrence, with potential in other malignant brain tumors. Overall design: Gene expression profiling was performed in triplicate by RNA sequencing in cell lines derived from primary and recurrent glioblastoma.  Along with the baseline expression, differential expression was determined after transduction with CRISPR sgRNAs targeting the AAVS1 locus or two individual guides targeting the PTP4A2 gene.