Abstract A020: Treatment of neuroblastoma with retinoic acid plus a KAT6A/B inhibitor induces sustained growth arrest and increases GD2 expression as a target for immunotherapy

Abstract Neuroblastoma is a malignancy of the peripheral sympathetic nervous system, accounting for 15% of childhood cancer deaths. Despite multi-modal treatment with systemic chemotherapy, surgery, radiation, two cycles of high-dose chemotherapy requiring stem cell rescue, and immunotherapy with anti-GD2 antibody treatment combined with retinoic acid, overall survival for patients is only about 50% and treatment -associated toxicity is immense. Thus, less toxic and more effective treatment options are desperately needed. Retinoic acid is clinically used to induce growth arrest of neuroblastoma cells and epigenetic rewiring of the enhancer landscape, leading to suppression of oncogenic MYCN expression. However, the epigenetic and growth suppressing effects of retinoic acid are completely reversible, leading to tumor re-growth. Here, we sought to identify epigenetic modifiers that enhance the antiproliferative effects of retinoids in neuroblastoma. In a drug screen with 452 compounds targeting epigenetic modifiers, we identified PF-9363, an inhibitor of the histone H3K23 acetyltransferases KAT6A/B, as synergistically enhancing neuroblastoma growth arrest in combination with retinoic acid, with a BLISS synergy score of 17 when both compounds are administered at 1µM each. Importantly, the combination treatment with retinoic acid plus PF-9363 resulted in durable growth arrest of neuroblastoma, which persisted beyond retinoid withdrawal in in vitro models, in contrast to single retinoid treatment. Durable growth arrest was due to sustained downregulation of MYCN and the essential transcription factors PHOX2B and GATA3, which was caused by gene expression silencing through deposition of H3K27me3 across their regulatory elements. In xenograft models of neuroblastoma in NSG mice, the KAT6A/B inhibitor PF-9363 alone demonstrated significant anti-tumor activity when given at 5 mg/kg daily by oral gavage and tumor volumes were significantly different compared to mice treated with vehicle starting at day 4 (p<0.01) through the end of treatment on day 28 (p<0.01). Moreover, the combination treatment with retinoic acid and PF-9363 also induced significant growth suppression starting from day 4 onward, compared to the vehicle control (p<0.01), and exhibited the most sustained growth suppressing effect among all treatment conditions even after retinoic acid was withdrawn on day 14, which was significantly different from retinoid treatment alone (p<0.05), where drug withdrawal led to rapid tumor proliferation. Furthermore, expression of GD2, a cell surface target for antibody therapy, was induced on GD2low neuroblastoma through the treatment with retinoic acid plus PF-9363 after 14 days of treatment determined by flow cytometry in vitro and immunofluorescence in vivo, rendering neuroblastoma cells more susceptible for anti-GD2 immunotherapy. Our studies nominate KAT6A/B inhibition as a novel approach to enhance the effectiveness of differentiation and immunotherapies in neuroblastoma and may be relevant for other tumors of neuro-ectodermal origin. Citation Format: Mark Zimmerman, Adam Durbin, Brian Abraham, Thomas Look, Francesca Alvarez-Calderon, Ulrike Gerdemann, Nina Weichert-Leahey. Treatment of neuroblastoma with retinoic acid plus a KAT6A/B inhibitor induces sustained growth arrest and increases GD2 expression as a target for immunotherapy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Functional and Genomic Precision Medicine in Cancer: Different Perspectives, Common Goals; 2025 Mar 11-13; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(5 Suppl):Abstract nr A020.