Abstract LB494: Neuroblastoma phenotypic switching is blocked by FHD-286, a small molecule inhibitor of the SWI/SNF ATPases SMARCA2/4

Abstract Neuroblastoma (NB) is a solid tumor derived from neural crest cells, characterized by high intra-tumoral heterogeneity and poor prognosis in high-risk cases. It exhibits two primary cellular phenotypes: adrenergic (ADRN) and mesenchymal (MES). The more lineage-committed ADRN subtype predominates in primary tumors, whereas the more chemoresistant MES subtype increases post-chemotherapy in relapsed tumors. The ability for NB tumors to control this phenotypic switching through epigenetic mechanisms contributes to their aggressiveness and chemotherapy resistance. One such epigenetic mechanism is SWI/SNF, a chromatin remodeling complex driven by the core ATPases SMARCA2 or SMARCA4 which facilitate nucleosome remodeling, enabling alterations in lineage specific gene expression. We have developed a model to study phenotypic switching in which PDX-derived NB cells cultured in media that supports neurosphere formation exhibit distinct ADRN and MES phenotypes and transcriptomes when shifted to standard culture media. Our research shows a SMARCA2/4 degrader reduces NB cell proliferation and suppresses the ability of NB neurospheres to elaborate a MES phenotype. We extended these studies to evaluate a clinically investigated small molecule inhibitor of SMARCA2/4 ATPases, FHD-286. FHD-286 effectively represses NB cell growth and prevented NB neurospheres from shifting to the MES cell subtype in standard culture media. As ADRN cells persist in the presence of SMARC2/4 inhibitors, we tested the effects of FHD-286 in combination with chemotherapy. FHD-286 demonstrated synergistic efficacy with etoposide, suppressing NB growth. The effects of this agent were also characterized by ATAC-seq and multiome single nuclei RNA- and ATAC-seq to identify impacted chromatin sites and gene expression changes. An evaluation of the combination of FHD-286 and etoposide in an in vivo PDX model is ongoing. Together, these findings establish FHD-286 as a novel therapeutic strategy for targeting chemoresistance and inhibiting NB plasticity and phenotypic switching and, when combined with cytotoxic agents, may be a promising agent for improving treatment outcomes for NB patients. Citation Format: Carly M. Sayers, Wendy Z. Fang, Jenna M. Lacy, Stefano Di Giulio, Xingyu Liu, Ming Sun, Zhihui Liu, Carol J. Thiele. Neuroblastoma phenotypic switching is blocked by FHD-286, a small molecule inhibitor of the SWI/SNF ATPases SMARCA2/4 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(8_Suppl):Abstract nr LB494.