Abstract LT005: Uncovering novel molecular vulnerabilities in PICALM::MLLT10 driven pediatric acute myeloid leukemia

Abstract Pediatric acute leukemia is the most common childhood cancer, and acute myeloid leukemia (AML) represents the second most frequent subtype, with overall survival rates of approximately 70% and relapse rates near 30%. The purpose of this study is to define molecular mechanisms essential for leukemogenesis and uncover potential vulnerabilities in a high-risk subtype of pediatric AML driven by the fusion oncoprotein PICALM::MLLT10. Our laboratory recently performed an integrated transcriptomic and genomic analysis of 887 pediatric AML cases, identifying 23 distinct molecular categories that differ in HOXA/HOXB expression, co-occurring mutations, and clinical outcomes. Among these, PICALM::MLLT10 AML is notable for its HOXA expression pattern similar to KMT2A-rearranged cases, yet it forms a distinct cluster with other immature AMLs on a UMAP projection, suggesting a unique transcriptional program. Leveraging genome-wide CRISPR screening data from the Cancer Dependency Map (DepMap) across 64 AML cell lines, we identified the RNA helicase DDX19A, but not its paralog DDX19B, as a selective genetic dependency in PICALM::MLLT10 models (U937, P31/FUJ) with an average Chronos score of -1.753 compared to -0.278 in all other AML models. Using a dTAG-induced degradation system, acute DDX19A depletion significantly impaired proliferation in PICALM::MLLT10-expressing cells and led to increased apoptosis as measured by Annexin V staining, and overexpression of DDX19A rescued the proliferation defect induced by dTAG13-mediated degradation. Domain-specific mutagenesis revealed that the DDX19A helicase and RNA-binding domains are essential for proliferation, while the NUP214-binding domains are dispensable in the PICALM::MLLT10 context. Next, we sought to define the transcriptional consequences of DDX19A loss in PICALM::MLLT10 cells. RNA-seq was performed on U937 cells expressing a FKBP12F36V-DDX19A allele after treatment with either DMSO or dTAG-13 for 24 hours, and pathway enrichment analysis revealed upregulation of cytoplasmic translation in DDX19A depleted cells. To functionally assess this effect, we measured nascent protein synthesis using O-propargyl-puromycin (OPP) incorporation after 24 hours of either DMSO or dTAG-13 treatment and observed a global reduction of protein synthesis in DDX19A depleted cells. These data establish DDX19A as a selective vulnerability and uncover the role of DDX19A in regulating protein synthesis in PICALM::MLLT10 driven pediatric AML. This work highlights a novel mechanistic vulnerability that may be leveraged for the development of targeted therapeutic strategies for this high-risk pediatric AML subtype. Citation Format: Lauren J. Ezzell, Ryan Hiltenbrand, Elizabeth Arnold, Michael P. Walsh, Melvin E. Thomas III, Tamara Westover, Masayuki Umeda, Jing Ma, Shondra M. Pruett-Miller, Jeffery M. Klco. Uncovering novel molecular vulnerabilities in PICALM::MLLT10 driven pediatric acute myeloid leukemia [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Fusion-Positive Cancer: From Discovery to Therapy; 2026 Jan 13-15; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(1_Suppl):Abstract nr LT005.