Abstract 392: Targeting drug-resistant acute myeloid leukemia (AML) clone using casein kinase II inhibitor
Authors: Mercer Katherine , Duke Koby , Rajaiah Rajesh , Daniyal Muhammad , Qiu Yi , Dovat Sinisa , Uzun Yasin , Zhang Lijun , Huang Suming , Klink Morgann , Gowda Chandrika 
Published: April 2023

Abstract
Introduction: Resistance to frontline cytotoxic therapy is rampant in AML. Molecular mechanisms promoting drug resistance are being identified to develop an effective strategy to overcome resistance. Protein kinase CK2 (casein kinase II) is a constitutively active, serine-threonine kinase that promotes cell survival and resistance to apoptosis in AML. A selective inhibitor of CK2, CX-4945 shows in vivo therapeutic efficacy in AML patient-derived xenografts. Here we report that CK2 kinase activity is high in AML cells resistant to cytarabine. Cytarabine-resistant cells are enriched for leukemia stem cells (CD34+/38-) and expansion of TP53 mutant clones. Specific inhibitors of CK2, CX4945 show selective cytotoxicity against the cytarabine-resistant cells.
Methods: We developed cytarabine-resistant AML cell lines (MOLM-13, MV4-11, U937, Kasumi-1). We used TP53 mutant clone isolated and expanded from cytarabine resistant MV4-11 cell line. Gene expression of cytarabine-resistant AML cells and that of cell lines with and without CX-4945 treatment was analyzed using RNA sequencing. mRNA expression of genes was measured using qPCR and protein level was measured using western blot. Drug response and drug synergy were assessed using MTT assay. AML patient-derived xenograft was used to evaluate in vivo therapeutic efficacy of the combination of cytarabine and CX-4945.
Results: Cytarabine-resistant cells have high expression of CK2. Gene expression analysis shows that the cytarabine metabolism gene is significantly altered in cytarabine-resistant cells and CX4945-treated AML cells. NT5C2 is a cytosolic nucleotidase that dephosphorylates monophosphates, preventing cytarabine from being phosphorylated to active form. hENT1 is a nucleoside transporter that brings cytarabine into the cells for metabolism. In cytarabine resistant cells, NT5C2 has been found to be high while hENT1 is low, preventing ideal cytarabine metabolism. CX4945 treatment decreased the expression of NT5C2 and increases expression of hENT1. Cytarabine sensitivity is restored following genetic inhibition (shRNA) or treatment with a CK2 inhibitor. AML xenograft mice treated with a combination of CX-4945 and cytarabine have decreased leukemia burden and prolonged survival compared to either drug alone.
Conclusion: These results suggest that: 1) Overactive CK2 promotes AML drug resistance in leukemia stem cells; 2) CK2 inhibitor CX-4945 selectively targets cytarabine-resistant cells; 3) The potential role of CK2 in leukemia stem cell survival and drug resistance in vivo needs further evaluation.
Citation Format: Katherine Mercer, Koby Duke, Rajesh Rajaiah, Muhammad Daniyal, Yi Qiu, Sinisa Dovat, Yasin Uzun, Lijun Zhang, Suming Huang, Morgann Klink, Chandrika Gowda. Targeting drug-resistant acute myeloid leukemia (AML) clone using casein kinase II inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 392.