Abstract 6825: Novel therapeutic strategies targeting MECOM rearranged AMLs discovered by unbiased drug screen

Abstract The MECOM locus at chromosome 3q26.2 encodes for the transcriptional regulator EVI1. In ∼10% of de novo AML, aberrant overexpression of EVI1 is observed. In approximately 50% of these it is due to inv(3)(q21;q26.2) or due to the chromosomal rearrangement [3q26.2-r], in which GATA2 enhancer is dislocated and drives EVI1 overexpression. 3q26.2-r AMLs tend to be more stem-like, exhibit therapy resistance and poor patient survival. To determine potential druggable targets, we conducted an unbiased drug screen in 3q26.2-r AML cell lines. We screened a library of over 2400 mechanistically annotated drugs (NCATS Mechanism Interrogation Plates), against seven AML cell lines (four 3q26.2-r and three non-3q26.2-r AML). Exploiting the mechanistic redundancy in the library, we identified target-level sensitivities in 3q26.2-r AML cells and relative activity as compared to other AML subtypes. Corroborating previous studies, in 3q26.2-r AMLs, BET protein inhibitors showed absolute sensitivity. We conducted RNA-seq and mass spectrometry analyses after BET inhibitor (BETi) mivebresib (ABBV-075) treatment. The findings revealed a significant overlap with the expression signature determined by RNA-seq and mass spectrometry performed after CRISPR knockout (KO) of EVI1. The dysregulated proteins included MYC, mTOR and TNF-alpha, indicating them to be potential targets or co-targets with BETi in 3q26.2-r AMLs. Since mTOR, PIK3CA, XIAP and Bcl-xL were also identified as druggable sensitivities in 3q26.2-r AML, we tested the activity of the combined mTOR/PI3K inhibitor dactolisib (BEZ235). Exposure to BEZ235 for 48 hours induced moderate levels of apoptosis in 3q26.2-r AML cell lines and patient-derived (PD) AML cells. This was associated with a decrease in the levels of the EVI1 targets, ERG, Bcl-xL, and c-Myc, as well as of c-Myb and EVI1, with simultaneous increase in the cleaved PARP levels. Combination of dactolisib with mivebresib exerted synergistic in vitro lethality in 3q26.2-r AML cell lines and PD AML blasts. Co-targeting with BETi and other identified sensitivities such as the IAP family inhibitor (LCL161) or Bcl-xL inhibitor (navitoclax or A1155463) also exhibited synergistic lethality in 3q26.2-r AML cell lines and PD AML cells. Importantly, compared to the vehicle control, monotherapy with mivebresib (BETi), dactolisib or LCL161 significantly reduced the AML burden and improved survival of the NSG mice in the xenograft models of 3q26.2-r AML. Co-treatment of mivebresib with dactolisib or LCL161 was superior than each drug alone in reducing AML burden and improving survival. These findings demonstrate promising preclinical activity of novel BETi-based combination with IAP or Bcl-xL inhibitor against AML with EVI1 overexpression. Citation Format: Christine E. Birdwell, Warren C. Fiskus, Christopher P. Mill, Tapan M. Kadia, Naval Daver, Courtney D. DiNardo, Koji Sasaki, John A. Davis, Kaberi Das, Hanxi Hou, Surbhi Sharma, Rashmi K. Shamanna, Michele Ceribelli, Kapil N. Bhalla. Novel therapeutic strategies targeting MECOM rearranged AMLs discovered by unbiased drug screen [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 6825.