Abstract 3797: Chromosome instability as a prognostic factor& an immunotherapeutic target in acute myeloid leukemia

Abstract

Abstract Chromosome instability (CIN) is an increased rate of chromosome mis-segregation due to errors in mitosis. CIN generates genetic and karyotypic diversity and is common in hematological malignancies. Low to moderate levels of CIN are well tolerated, and moderate levels can promote cancer proliferation by generating genetic diversity for tumor evolution. However, very high levels of CIN are lethal and enhancing CIN can be therapeutic. Therefore, CIN status could be prognostic for clinical outcomes as well as a therapeutic target. Despite its promise, little is known about CIN in AML. We first determined if CIN is correlated with clinical outcome in patients with acute myeloid leukemia (AML). We quantified the chromosome mis-segregation frequency (lagging chromosomes and chromatin bridges) in dividing AML cells on bone marrow core biopsies. Our study reveals a wide distribution of CIN in AML core biopsy specimens, ranging from 20% to 67%. High CIN correlates with a better overall survival in patients with AML. Recent data suggest that chromosome mis-segregation promotes senescence and initiates immune clearance. Our hypothesis is that chromosome instability is immunogenic due to DNA damage, proteotoxic/oxidative stress with a high mutagenic potential, which can be recognized by immune system. To test this, we used an inhibitor of Monopolar spindle 1 (Mps1) to enhance CIN and tested if that altered immunogenicity. Mps1 is a key component of the mitotic checkpoint and is also involved with chromosome alignment. Inhibition of Mps1 by AZ3146 results in severe chromosome mis-segregation, micronuclei formation, and apoptosis in AML cell lines. In addition, AZ3146 treatment causes activation of γH2AX due to DNA damage, and calreticulin exposure from endoplasmic reticulum stress. This generates danger signals to activate innate immune system (natural killer cells and dendritic cells) and induces immunogenic cell death (ICD) through priming of cytotoxic T cells. This effect is mainly seen in synchronized mitotic cells, suggesting AZ3146 acts specifically on mitosis. Additionally, we observed the overexpression of programed death ligand-1 (PD-L1) after the treatment of AZ3146 in AML cells. As evidence showed, PD-L1 participates in the immune evasion and protects AML blasts from cytotoxic T cells in mouse models of leukemia. Taken together, our observations in Mps1 inhibitor treatment indicate the immunogenicity of CIN in AML. Additionally, these data support combination treatment of mitotic checkpoint inhibitor with immunotherapy to improve therapeutic efficacy in AML patients. Citation Format: Ning Jin, Mark Burkard. Chromosome instability as a prognostic factor& an immunotherapeutic target in acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3797.