Abstract 6730: Oncogenic ASPP2kappa (k) drives leukemic transformation and disease progression

Abstract Introduction: Despite tremendous efforts and new therapeutics, acute myeloid leukemia (AML) remains difficult to treat and therapy outcome is far from satisfactory for many patients. We have recently identified a novel, oncogenic isoform of the tumor suppressor ASPP2, named ASPP2k, which is expressed in >50% of AMLs, and have demonstrated that deregulation of the ASPP2/ASPP2k - p53 axis associates with drug resistance and a more aggressive tumor biology. We now show that ASPP2k drives leukemic transformation and disease progression in vivo and proves to be a potent therapeutic target. Methods: Isogenic AML ASPP2κ silenced (KD) (Molm14, HL60 and ex vivo patient blasts) were established and xenotransplanted into NSG mice. Ba/F3 interleukin-3 dependent pro-B cells, engineered to overexpress ASPP2k were transplanted into immunocompetent C3H mice to study the influence of ASPP2k on the tumor microenvironment. Disease development and progression were monitored using an IVIS Lumina imaging system. In addition, we designed and tested novel, fully chemically modified ASPP2k-specific siRNAs for in vivo application. Results: All in vivo models demonstrate earlier leukemia development and engraftment as well as a more aggressive course of disease in dependency of ASPP2k expression (lifespan 30 vs 42 days pi for EV and KD, 22d for KI, p<0,001), underlined by higher WBC count (p<0,001), spleno- and hepatomegaly (p<0,0001) early weight loss (p<0,01) and dissemination into brain and lungs (p<0,001). Importantly, Ba/F3 cells lost their IL-3 dependency upon over-expression of ASPP2k, considered a first step of malignant transformation (proliferation +120 fold-change at 96h for KI vs EV). C3H mice transplanted with ASPP2k overexpressing Ba/F3 cells demonstrated higher organ infiltration (eg liver p<0,001) and a strong immune response, as evidenced by upregulation of secretion of pro-inflammatory cytokines like MIP-2, STNFRI, VCAM-1, PF-4, L-selectin, OPG, CD26, MIG proteins, among others as well as significant T-cell infiltration (p<0,01). Most importantly, employing novel, fully chemically modified ASPP2k-specific siRNAs, we were able to silence ASPP2k in vivo and again attenuate leukemia progression. Summary: In summary, we here show that ASPP2k directly contributes to aggressiveness of the disease in vivo and provide a first rational to further develop ASPP2k specific siRNAs as a novel therapeutic approach to combat leukemia. Future studies evaluating ASPP2k as a potential target for therapy are warranted. Citation Format: Alessia Ruiba, Anna-Lena Ahrens, Vanessa Aellig, Reka Haraszti, Marcus M. Schittenhelm, Kerstin Maria Kampa-Schittenhelm. Oncogenic ASPP2kappa (k) drives leukemic transformation and disease progression [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 6730.