Abstract A060: Targeting DRD2 dysregulation in recurrent glioblastoma with imipridone ONC201: predictive and pharmacodynamic clinical biomarker analyses
Authors: Prabhu Varun Vijay , Madhukar Neel , Kline C. Leah B. , Tarapore Rohinton , El-Deiry Wafik , Elemento Olivier , Doherty Faye , VanEngelenburg Alexander , Durrant Jessica , Zloza Andrew , Benes Cyril , Arrillaga Isabel , Oster Wolfgang , Allen Joshua E. 
Published: August 2018

Abstract
Background: ONC201, an imipridone that is a selective antagonist of the G protein-coupled receptors dopamine receptor D2 (DRD2) and D3 (DRD3), has exhibited biologic activity and an exceptional safety profile in a phase II study in bevacizumab-naïve recurrent glioblastoma (Arrillaga et a.l, 2017). Single-agent ONC201 efficacy has been observed in preclinical glioblastoma models in addition to robust penetrance of the blood-brain barrier (Allen et al., 2013). DRD2 antagonism induces tumor cell apoptosis via the same signaling pathways affected by ONC201. In addition, DRD2 is expressed on NK and other immune cells and DRD2 antagonism can induce their activation. Methods: Cell viability assays were performed with ONC201 in &gt;1000 Genomic of Drug Sensitivity in Cancer (GDSC) cell lines and NCI60. Immunohistochemistry staining of DRD2/DRD5 was performed in glioblastoma tissue microarrays and archival tumor tissues. Whole exome sequencing was performed in RKO cells with acquired resistance to ONC201. DRD5 wild-type and mutant constructs were generated for overexpression studies. ELISA was used to quantitate serum prolactin and immune effector (perforin) levels. Intratumoral drug concentrations were evaluated by LC-MS assays conducted on glioblastoma tissue resected from patients following the second dose of 625mg ONC201. Results: Evaluation of ONC201 in GDSC cell lines confirmed broad anticancer efficacy with high sensitivity (~1-3 µM) in human brain cancer. The Cancer Genome Atlas (TCGA) revealed that DRD2 is highly expressed in glioblastoma relative to other dopamine receptors and that genetic aberrations are rare. High expression of DRD2 occurred in primary, rather than secondary, glioblastoma and was associated with a poor prognosis. Immunohistochemistry of tissue microarrays revealed DRD2 overexpression in glioblastoma relative to normal brain. A linear correlation between DRD2 mRNA and ONC201 GI50 was observed among glioblastoma cell lines in the NCI60 panel. Interestingly, expression of DRD5, a D1-like dopamine receptor that counteracts DRD2 signaling, was significantly inversely correlated with ONC201 potency in the NCI60 and GDSC datasets (P &lt;.05). Furthermore, a missense DRD5 mutation was identified in cancer cells with acquired resistance to ONC201. Resistance could be recapitulated with overexpression of the mutant or wild-type DRD5 gene. A significant induction of serum prolactin, a surrogate biomarker of target engagement, was detected upon ONC201 administration to recurrent glioblastoma patients. Intratumoral drug concentrations surpassed therapeutic levels, ranging from ~0.6-10µM at 24 hours post-dose. Immune effector levels in the serum correlated with the kinetics of a durable objective response observed in a patient with an H3.3 K27M glioma. Among the 15 available archival tumor tissue specimens, all had expression of DRD2 and 8/17 patients had low expression of DRD5. Patients with PFS&gt;5 month had no detectable expression of DRD5, unlike those with PFS&lt;5 months. In addition, 4/8 DRD2+DRD5- and 0/7 DRD2+DRD5+ patients are still alive with a median follow-up of 47.4 weeks. Conclusion: The dopamine receptor pathway is a novel therapeutic target that is dysregulated in glioblastoma and provides predictive and pharmacodynamic biomarkers of tumor sensitivity to ONC201.
Citation Format: Varun Vijay Prabhu, Neel Madhukar, C. Leah B. Kline, Rohinton Tarapore, Wafik El-Deiry, Olivier Elemento, Faye Doherty, Alexander VanEngelenburg, Jessica Durrant, Andrew Zloza, Cyril Benes, Isabel Arrillaga, Wolfgang Oster, Joshua E. Allen. Targeting DRD2 dysregulation in recurrent glioblastoma with imipridone ONC201: predictive and pharmacodynamic clinical biomarker analyses [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A060.