Abstract 3271: The casein kinase 2/IKZF1 axis attenuates ceramide accumulation through up-regulation of acid ceramidase: Implications for use of CK2 inhibitors in high-risk pediatric B-cell acute lymphoid leukemia
Authors: Hengst Jeremy A. , Tukaramrao Diwakar Bastihalli , Fox Todd , Sharma Arati , Desai Dhimant , Dovat Sinisa 
Published: March 2024

Abstract
Casein Kinase II (CK2), a growth-promoting non-oncogene, is frequently over-expressed in pediatric high-risk B-cell acute lymphoblastic leukemia (B-ALL) leading to proliferation and survival. CK2 phosphorylates the tumor suppressor IKZF1 (IKAROS) resulting in a loss-of DNA-binding activity. Loss of IKZF1 function is associated with poor prognosis in high-risk B-ALL. As such, inhibition of CK2 using silmitasertib (CX-4945), to restore IKZF1 function, is being therapeutically investigated in high-risk B-ALL. CK2 also phosphorylates/activates the mammalian ceramide synthases to increase production of the pro-apoptotic sphingolipid, ceramide (Cer). Therefore, we hypothesized that inhibition of CK2 with CX-4945 would exert both pro-death (restoration of IKAROS function) and pro-survival (decreased Cer production) effects on B-ALL cells. Moreover, this suggests that targeting the sphingolipid metabolic pathway in tandem with CX-4945 could be a novel strategy for treatment of high-risk B-ALL. To this end, we examined the effects of CX-4945 on sphingolipid levels and the enzymes of the sphingolipid metabolic pathway. Unexpectedly, we determined that CX-4945 dose-dependently increased expression of ceramide synthase 1 (CERS1) and acid ceramidase (AC) proteins, in an IKZF1 dependent manner. Increased CERS1 expression/production of C18:0 Cer has been linked to enhanced mitophagy (i.e., lysosomal clearance of damaged mitochondria) in head and neck squamous cell carcinoma. Induction of mitophagy by CX-4945 was confirmed by western blot analysis of mitofusin-1 and Drp-1 levels. Up-regulation of AC, a lysosomal protein, metabolizes C18:0 Cer to sphingosine for recycling and prevents Cer-induced lysosomal membrane permeabilization. Thus, induction of mitophagy and metabolic breakdown of Cer could potentially reduce the apoptotic efficacy of CX-4945 in B-ALL cell lines. We, therefore, tested whether inhibition of AC would synergize with CX-4945 to enhance B-ALL cell death. Indeed, synergy was observed with the AC inhibitor, SACLAC, in multiple cell lines. Consistent with the observation of synergy between CX-4945 and SACLAC, the combination also enhanced cleavage of PARP indicating an enhancement of cell death. We are currently testing the efficacy of a combination of CX-4945 and AC inhibitors in cell-line derived xenograft models of human B-ALL. Together, these findings indicate that simultaneous targeting of CK2 and AC represents a rationally selected combinatorial therapeutic strategy that overcomes the ability of cancer cells to adapt to single agent targeted therapies by altering pro- and/or anti-apoptotic pathways.
Citation Format: Jeremy A. Hengst, Diwakar Bastihalli Tukaramrao, Todd Fox, Arati Sharma, Dhimant Desai, Sinisa Dovat. The casein kinase 2/IKZF1 axis attenuates ceramide accumulation through up-regulation of acid ceramidase: Implications for use of CK2 inhibitors in high-risk pediatric B-cell acute lymphoid leukemia [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(6_Suppl):Abstract nr 3271.