Common resistance mechanisms to deoxynucleoside analogues in variants of the human erythroleukaemic line K562

Abstract

Summary. Resistant variants of the human leukaemic line K562 were developed using selection with the deoxynucleoside analogues cytosine arabinoside, 2-chlorodeoxyadenosine, udarabine and gemcitabine. The resistant lines displayed a high degree of cross resistance to all deoxynucleoside analogues, with little or no cross resistance to other agents. There was a profound accumulation defect of all nucleoside analogues in the resistant variants but no signi®cant defect in nucleoside transport in any of the variants. 5H nucleotidase activity was strongly increased and deoxycytidine kinase activity was moderately reduced in all of the resistant variants, resulting in reduced accumulation of triphosphate analogues. In addition a deletion in one of the alleles of the deoxycytidine kinase was detected in thē udarabine-resistant line. Ribonucleotide reductase activity was found to be strongly increased in the gemcitabineselected line and purine nucleoside phosphorylase was increased in the 2-chlorodeoxyadenosine-selected line. Free nucleotide pools were increased in the 2-chlorodeoxyadenosineselected line. There was no expression of the mdr1 gene by the resistant lines. Karyotypic analysis and FISH experiments using a 6q21 speci®c probe showed alterations in the 6(q16-q22) region which contains the 5 H -nucleotidase gene. Early events in the activation and degradation of deoxynucleoside analogues appear to constitute common mechanisms of resistance to these compounds.

Nucleoside analogues: mechanisms of drug resistance and reversal strategies

“…30,31 The catabolism of ara-C results from rapid deamination by cytidine deaminase (CDD) to the non-toxic metabolite arabinoside uridine while ara-CMP is dephosphorylated by the action of cytoplasmic 5Ј-nucleotidase (5Ј-NU). 32 Ara-C cytotoxicity is believed to result from a combination of DNA polymerase inhibition and from incorporation of ara-CTP into…”

“…[106][107][108][109] Transfection of the dCK gene in dCK-deficient tumor cell lines restores in vitro sensitivity to ara-C. 110,111 Moreover, in vitro models have shown crossresistance between 2-CdA, gemcitabine, fludarabine and ara-C with reduced dCK activity as the underlying determinant of resistance. 109,112 It is noteworthy that in vitro only significant reductions in the levels of dCK activity (10% or less) are associated with a resistant phenotype, suggesting that under baseline conditions dCK is present in excess.…”

“…142,143 In vitro, increased 5Ј-NU activity has been consistently associated with nucleoside drug resistance. 45,58,109 In the clinic, levels of cyto-5Ј-NU activity have been correlated to clinical response in CLL, HCL and AML (Table 4). In CLL and HCL, Kawasaki et al 119 demonstrated that pretreatment levels of high K m 5Ј-NU allowed prediction of 2-CdA responsiveness, since 5Ј-NU levels were significantly lower in responders than in non-responding patients.…”

Genetic factors influencing Pyrimidine-antagonist chemotherapy

“…157 The balance between dCK and 5NT might predict drug toxicity, since strongly increased 5NT activity combined with reduced dCK activity was observed in a human leukaemic cell line, resistant to ara-C and dFdC. 158 Apart from resistance to nucleoside analogues caused by aberrant drug metabolism, altered drug transport may cause decreased chemosensitivity. Recently, overexpression of the human multidrug resistance protein 5 (MRP5), an ABC transporter known to transport nucleotide monophosphates, has been associated with resistance to dFdC in vitro.…”

Gene expression profilers and conventional clinical markers to predict distant recurrences for premenopausal breast cancer patients after adjuvant chemotherapy

“…To find the reporters on our array corresponding to the genes on our pre-defined gene lists, we used the official gene symbol. The gene symbols for the van 't Veer gene list (16) were obtained through ACID (39) using UniGene build 176, and the official gene symbols for the drug-genes were found manually using Gene and Locus Link. All reporters on our array that according to UniGene build 180 had a gene symbol represented on the resulting list were selected.…”