Abstract
BackgroundCytarabine (ara-C) is the major drug for the treatment of acute myeloid leukemia (AML), but cellular resistance to ara-C is a major obstacle to therapeutic success. The present study examined enhanced anti-apoptosis identified in 3 newly established nucleoside analogue-resistant leukemic cell line variants and approaches to overcoming this resistance.MethodsHL-60 human AML cells were used to develop the ara-C– or clofarabine (CAFdA)-resistant variants. The Bcl-2 inhibitor venetoclax and the Mcl-1 inhibitor alvocidib were tested to determine whether they could reverse these cells’ resistance.ResultsA 10-fold ara-C-resistant HL-60 variant, a 4-fold CAFdA-resistant HL-60 variant, and a 30-fold CAFdA-resistant HL-60 variant were newly established. The variants demonstrated reduced deoxycytidine kinase and deoxyguanosine kinase expression, but intact expression of surface transporters (hENT1, hENT2, hCNT3). The variants exhibited lower expression of intracellular nucleoside analogue triphosphates compared with non-variant HL-60 cells. The variants also overexpressed Bcl-2 and Mcl-1. Venetoclax as a single agent was not cytotoxic to the resistant variants. Nevertheless, venetoclax with nucleoside analogs demonstrated synergistic cytotoxicity against the variants. Alvocidib as a single agent was cytotoxic to the cells. However, alvocidib induced G1 arrest and suppressed the cytotoxicity of the co-administered nucleoside analogs.ConclusionsThree new nucleoside analogue-resistant HL-60 cell variants exhibited reduced production of intracellular analogue triphosphates and enhanced Bcl-2 and Mcl-1 expressions. Venetoclax combined with nucleoside analogs showed synergistic anti-leukemic effects and overcame the drug resistance.
Highlights
Cytarabine is the major drug for the treatment of acute myeloid leukemia (AML), but cellular resistance to ara-C is a major obstacle to therapeutic success
Nishi et al BMC Cancer (2020) 20:984 intracellularly converted to the monophosphate form by deoxycytidine kinase and to the triphosphate form, ara-C 5′-triphosphate, an intracellular active metabolite of ara-C, by pyrimidine kinases
CAFdA is transported by human equilibrative nucleoside transporter 1 (hENT1), Human equilibrative nucleoside transporter 2 (hENT2), and human concentrative nucleoside transporter 3
Summary
Cytarabine (ara-C) is the major drug for the treatment of acute myeloid leukemia (AML), but cellular resistance to ara-C is a major obstacle to therapeutic success. Cytarabine (1-β-D-arabinofuranosylcytosine; ara-C) is the major chemotherapeutic agent for acute myeloid leukemia (AML) [1, 2]. Ara-C, a nucleoside analog, is taken up by leukemic cells via the membrane transporter human equilibrative nucleoside transporter 1 (hENT1) [6, 7]. Clofarabine (2-chloro-9-[2-deoxy-2-fluoro-β-D-arabinofuranosyl] adenine, CAFdA), a nucleoside analog similar to ara-C, is pharmacologically more advantageous than ara-C [10, 11]. CAFdA is transported by hENT1, hENT2, and human concentrative nucleoside transporter 3 (hCNT3). Similar to ara-C, CAFdATP is inserted into DNA, resulting in S-phasespecific cytotoxicity [12]. CAFdA is used widely to treat AML in relapsed/refractory settings [13]
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