Abstract 2601: KAT6A and B inhibition increases efficacy of differentiation and GD2 targeting immunotherapy in neuroblastoma

Abstract Neuroblastoma is a malignancy of the peripheral sympathetic nervous system, accounting for 15% of childhood cancer deaths. Despite multi-modal treatment regimens and post-consolidation therapy, including anti-GD2 antibody treatment combined with retinoic acid, overall survival for patients with high-risk disease is only ∼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 and B, as synergistically inhibiting neuroblastoma growth in combination with retinoic acid. Importantly, this growth suppression was durable and persisted beyond retinoid withdrawal in in vitro models, in contrast to retinoid treatment alone. Durable growth suppression was due to sustained downregulation of MYCN and the essential transcription factors PHOX2B and GATA3, caused by gene expression silencing through PRC2-dependent deposition of H3K27me3 across their regulatory enhancers. In NSG xenograft models of neuroblastoma, 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 vehicle treated mice starting at day 4 through the end of treatment on day 28. Moreover, the combination treatment with retinoic acid and PF-9363 exhibited profound and sustained growth suppression compared to vehicle treated mice and exhibited the most sustained growth suppressing effect among all treatment conditions, persisting even after retinoic acid was withdrawn. This outcome was significantly different from retinoid treatment alone, where drug withdrawal resulted in rapid tumor proliferation in NSG mice. Reflecting the epigenetic reprogramming of these tumor cells, we observed that expression of GD2, a cell surface glycosphingolipid that is a target of antibody-based and CAR T cell therapies in neuroblastoma, was induced on GD2low neuroblastoma cells by treatment with retinoic acid plus PF-9363 both in vitro and in vivo, leading to increased effectiveness of anti-GD2 CAR T cell therapy in neuroblastoma. These studies nominate KAT6A/B inhibition as a novel approach to enhance the effectiveness of differentiation and GD2-immunotherapy in neuroblastoma and may be relevant for other tumors of neuro-ectodermal origin. Citation Format: Nina Weichert-Leahey, Alla Berezovskaya, Mark W. Zimmerman, Francesca Alvarez-Calderon, Ulrike Gerdemann, Silvi Salhotra, Nathaniel Mabe, Adam D. Durbin, Kimberly Stegmaier, Brian J. Abraham, A. Thomas Look. KAT6A and B inhibition increases efficacy of differentiation and GD2 targeting immunotherapy in neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2601.