Abstract 2852: Novel combination therapy with a KAT6A/B inhibitor together with retinoids induces irreversible differentiation of neuroblastoma cells

Abstract Neuroblastoma is a pediatric tumor of the peripheral sympathetic nervous system derived from migratory neural crest cells that have committed to become sympathetic neuroblasts, but their definitive differentiation is blocked. Neuroblastoma cell identity depends on the adrenergic core regulatory circuit (CRC) of transcription factors that collaborate with MYCN to drive cell proliferation and the oncogenic gene expression program. Retinoic acid is used as differentiation therapy for patients with high-risk neuroblastoma, with the goal to block proliferation and drive sympathetic neuronal differentiation. We recently showed that retinoic acid re-organizes the enhancer landscape of neuroblastoma and promotes a new retino-sympathetic cell state characterized by MYCN downregulation, proliferative arrest, and sympathetic neuronal differentiation. However, the effects of retinoic acid on epigenetic rewiring of the adrenergic CRC and suppression of MYCN expression are reversible in vitro and in vivo, leading to tumor re-growth when the retinoic acid is withdrawn. Therefore, we sought to determine if retinoid-induced differentiation can be forced to progress to irreversible neuronal maturation by the addition of inhibitors of epigenetic modifying enzymes. Here, we conducted a drug screen of epigenetic modifying drugs alone and in combination with retinoic acid to determine their effects on neuroblastoma cell growth and differentiation. In this screen, we found that an inhibitor of the histone H3K23 acetyltransferases KAT6A/B, PF-9363, synergistically inhibits neuroblastoma cell growth in combination with retinoic acid. Moreover, retinoid-resistant neuroblastoma cell lines can be sensitized to retinoic acid when combined with a KAT6 inhibitor. Importantly, this combination treatment renders the differentiated cell state irreversible, such that it is maintained after retinoic acid is withdrawn, with continued suppression of the adrenergic CRC and MYCN expression. In conclusion, the retino-sympathetic differentiated cell state induced by retinoic acid in neuroblastoma becomes irreversible when the cells are also treated with an inhibitor of the KAT6A/B histone H3K23 acetyltransferases, implicating the essential role of these enzymes in restoring the proliferative immature progenitor phenotype in adrenergic neuroblastoma cells. Citation Format: Nina Weichert-Leahey, Alla Berezovskaya, Mark Zimmerman, Brian J. Abraham, Adam W. Durbin, A Thomas Look. Novel combination therapy with a KAT6A/B inhibitor together with retinoids induces irreversible differentiation of neuroblastoma cells abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2852.