Abstract 7123: Biomarker-targeted alkylator and DNA damage repair inhibitor combination for refractory and relapsed acute myeloid leukemia (AML)

Abstract Isocitrate dehydrogenase 1 and 2 (IDH1/2) convert isocitrate to α-ketoglutarate in the tricarboxylic acid (TCA) cycle. A missense mutation in IDH1/2 leads to accelerated conversion of α-ketoglutarate into 2-hydroxyglutarate (2-HG), an oncometabolite that competitively inhibits α-ketoglutarate-dependent dioxygenases including Ten-Eleven Translocation (TET) enzymes. TET enzymes are DNA demethylases that convert 5-methylcytosine to 5-carboxycytosine and regulate CpG island promoter methylation signatures. In IDH1/2 mutant glioma, inhibition of TET2 enzyme by 2-HG can lead to promoter hypermethylation of O6-methylguanine methyltransferase (MGMT) and reduce its expression. Approximately 10-15% of de novo or treatment-related AML harbor mutually exclusive mutations in IDH1/2 or TET2, and emerging resistance towards clinical IDH1/2 inhibitors, therefore warrants novel therapeutic options. We performed a pan-cancer TCGA analysis and observed MGMT promoter hypermethylation and reduced expression in IDH1/2 AML. Our independent study on 10 AML patients (5 IDH1/2 and 5 TET2 mutant) corroborated the TCGA data and showed a significantly reduced expression of MGMT in comparison to 7 wild-type AML samples. As MGMT resolves O6-alkylguanine lesions during DNA damage, we performed an exhaustive alkylator screen, where temozolomide (TMZ) and our novel compound KL-50 emerged as the top hits that imparted a maximum therapeutic index in multiple MGMT (MGMT+/–) isogenic AML cell line models. Both TMZ and KL-50 induced MGMT-dependent DNA strand breaks and replication stress and activated ATM and ATR DNA damage response pathways in a time-dependent manner. Inhibition of ATR activation with Ceralasertib, an ATR inhibitor (ATRi) currently in clinical trials for chronic myelomonocytic leukemia and myelodysplastic syndromes, imparted a profound MGMT-dependent synergy with TMZ and KL-50. Researchers have established in glioma that mismatch repair (MMR) loss confers resistance to TMZ, and reported studies also show evidence of MMR loss in refractory or relapsed AML patients. Thus, we developed numerous MMR-deficient isogenic AML cell lines in an MGMT+/– background and observed MMR loss-mediated resistance to TMZ and abrogation of its synergy with ATRi. Unlike TMZ, KL-50 retained a profound synergy with ATRi in an MGMT-dependent manner irrespective of MMR status. We are currently investigating our novel KL-50 and ATRi combination in MGMT/MMR isogenic cell line-based in vivo AML models and in AML patient-derived xenografts to establish it as a promising novel biomarker-targeted therapy for AML patients. Citation Format: Prateek Bhardwaj, Ranjini Sundaram, Amro Baassiri, Martin Matthews, Jennifer VanOudenhove, Susan Gueble, Stephanie Halene, Ranjit Bindra. Biomarker-targeted alkylator and DNA damage repair inhibitor combination for refractory and relapsed acute myeloid leukemia (AML) 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 7123.