Abstract 5592: HMGA1 modulates chromatin state and transcriptional networks involved in plasticity in refractory myeloid leukemia

Abstract Although High Mobility Group A1 (HMGA1) chromatin regulators are overexpressed in refractory acute myeloid leukemia (AML) and diverse solid tumors, targetable mechanisms underlying HMGA1 remain elusive. HMGA1 is highly expressed in stem cells and poorly differentiated cancers where it modulates chromatin structure to activate developmental gene networks. In AML arising from JAK2V617F myeloproliferative neoplasms (MPN), HMGA1 is required for leukemogenesis by inducing transcriptional networks that drive aberrant proliferation and cell fate. Like MPN AML, KMT2A-rearranged (KMT2A-r) AML is refractory to therapy and highly lethal. KMT2A-r AML is caused by rearrangements of the KMT2A gene, which encode abnormal fusion proteins that induce pro-leukemogenic genes, including HOX genes. While prior work identified KMT2A fusion partners and protein complexes, this has not led to better therapies for most patients. We therefore sought to examine HMGA1 function in KMT2A-r AML. We hypothesized that: 1) HMGA1 drives plasticity in KMT2A-r AML by altering chromatin state and transcriptional networks, and, 2) Targeting HMGA1 will enhance sensitivity to therapy. In two KMT2A-r AML patient cohorts, HMGA1 is highly overexpressed compared to CD34+ stem and progenitors from healthy controls, suggesting it drives leukemogenesis. To define HMGA1 function, we silenced HMGA1 using CRISPR or short hairpin RNA in KMT2A-r cell lines (MOLM-14, THP-1, MV4-11). Strikingly, silencing HMGA1 disrupts proliferation and clonogenicity in vitro, while prolonging survival in immunosuppressed mice transplanted with KMT2A-r AML cells. Intriguingly, leukemic cells that engraft in the bone marrow from the pool of cells with HMGA1 silencing express higher levels of HMGA1, suggesting that escape from gene silencing and a specific level of HMGA1 is required for leukemic engraftment and expansion. HMGA1 also increases in KMT2A-r AML cells that become resistant to cytarabine (AraC), suggesting that HMGA1 endows AML cells with the capacity to survive and expand after AraC. Because repression of tumor suppressors was recently defined as a mechanism of therapy resistance in AML, we also examined tumor suppressor pathways in both JAK2V617F and KMT2A-r AML. Intriguingly, HMGA1 occupies the promoter region of the CDKN1A locus by chromatin immunoprecipitation and represses its expression in KMT2A-r and JAK2V617F AML cells. To define additional mechanisms underlying HMGA1 in KMT2A-r AML, multi-omics studies are underway. In preliminary work thus far, we also found that HMGA1 induces HOX genes. Together, these findings implicate HMGA1 as a promising therapeutic target and novel epigenetic regulator in KMT2A-r AML by altering chromatin state and downstream gene expression. Citation Format: Bailey E. West, Jung-Hyun Kim, Audrey-Ann Supreme, Iliana Herrera, Zanshé Thompson, Li Z. Luo, Faiza Shaik, Joseph Kim, Hyunsung Woo, Soheil Meshinchi, Rhonda E. Ries, Linda M. Resar. HMGA1 modulates chromatin state and transcriptional networks involved in plasticity in refractory myeloid leukemia 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 5592.