Clofarabine exerts antileukemic activity against cytarabine‐resistant B‐cell precursor acute lymphoblastic leukemia with low deoxycytidine kinase expression

Abstract

Cytosine arabinoside (Ara‐C) is one of the key drugs for the treatment of acute myeloid leukemia. It is also used for consolidation therapy of acute lymphoblastic leukemia (ALL). Ara‐C is a deoxyadenosine analog and is phosphorylated to form cytosine arabinoside triphosphate (Ara‐CTP) as an active form. In the first step of the metabolic pathway, Ara‐C is phosphorylated to Ara‐CMP by deoxycytidine kinase (DCK). However, the current cumulative evidence in the association of the Ara‐C sensitivity in ALL appears inconclusive. We analyzed various cell lines for the possible involvement of DCK in the sensitivities of B‐cell precursor ALL (BCP‐ALL) to Ara‐C. Higher DCK expression was associated with higher Ara‐C sensitivity. DCK knockout by genome editing with a CRISPR‐Cas9 system in an Ara‐C‐sensitive‐ALL cell line induced marked resistance to Ara‐C, but not to vincristine and daunorubicin, indicating the involvement of DCK expression in the Ara‐C sensitivity of BCP‐ALL. DCK gene silencing due to the hypermethylation of a CpG island and reduced DCK activity due to a nonsynonymous variant allele were not associated with Ara‐C sensitivity. Clofarabine is a second‐generation deoxyadenosine analog rationally synthesized to improve stability and reduce toxicity. The IC50 of clofarabine in 79 BCP‐ALL cell lines was approximately 20 times lower than that of Ara‐C. In contrast to Ara‐C, although the knockout of DCK induced marked resistance to clofarabine, sensitivity to clofarabine was only marginally associated with DCK gene expression level, suggesting a possible efficacy of clofarabine for BCP‐ALL that shows relative Ara‐C resistance due to low DCK expression.

Association of aberrantASNSimprinting with asparaginase sensitivity and chromosomal abnormality in childhood BCP-ALL

“…We investigated methylation status by sequencing 19 CG dinucleotides of bisulfite PCR products using NGS technology. 32,33 Histograms of the mean percent methylation in each read of NGS revealed an unmethylated pattern in mouse fetal, neonatal, and adult tissues (Figure 1C). We next investigated the methylation status of the human ASNS gene.…”

Clofarabine increases the eradication of minimal residual disease of primary B-precursor acute lymphoblastic leukemia compared to high-dose cytarabine without improvement of outcome. Results from the randomized clinical trial 08-09 of the Cooperative Acute Lymphoblastic Leukemia Study Group

“…Clofarabine is a second-generation purine nucleoside analogue that combines the positive characteristics of first-generation purine nucleosides fludarabine and cladribine by retaining 2-halogenated adenines, resulting in improved resistance against deamination and phosphorolysis. [1][2][3] Several studies have been launched which scrutinized clofarabine in combination with other cytostatic drugs as second-or third-line therapy, or as a bridging regimen to hematopoietic stem cell transplantation. [4][5][6] In Children's Oncology Group (COG) trial AALL1131, clofarabine was administered in combination with etoposide and cyclophosphamide, which were associated with severe infections and persistent myelotoxicity leading to premature closure of the experimental clofarabine arm.…”

IMiDs uniquely synergize with TKIs to upregulate apoptosis of Philadelphia chromosome-positive acute lymphoblastic leukemia cells expressing a dominant-negative IKZF1 isoform

“…[ 3 H]-thymidine uptake assays were performed as described previously 43 . Percentage inhibition was calculated as follows: {[(cpm of treated)/(cpm of untreated)] − 1} × 100.…”