title: Pharmacological basis for cladribine resistance in a human acute T lymphoblastic leukaemia cell line selected for resistance to etoposide.
abstract: Cross-resistance between different classes of anti-neoplastic agents can jeopardize successful combination cancer chemotherapy. In this study, we observed an unexpected cross-resistance between the podophyllotoxine derivative etoposide (VP) and the nucleoside analogue cladribine (CdA) in CCRF-CEM cells developed for resistance to VP. The resistant cells also displayed 14- and twofold resistance to cytarabine (ara-C) and gemcitabine respectively. Closer analysis of these cells showed that they contained lower amounts of topoisomerase (topo) IIalpha (P < 0.001) and beta protein (P < 0.026), formed substantially lower amounts of the topo II-DNA complex, and had a markedly decreased level of Fas (CD95/APO-1)-ligand mRNA expression. Interestingly, Fas expression in the resistant cells did not differ from that in the parental cell line. No differences were observed in the accumulation/efflux of daunorubicin or in the gene expressions of P-glycoprotein, multidrug resistance-associated protein and the lung resistance-related protein. The activity of deoxycytidine kinase (dCK), responsible for activation of CdA and ara-C, was the same for resistant and wild-type cells. However, there was an increase in the activity of the cytosolic 5'-nucleotidases (5'-NT), responsible for deactivation of nucleotides, amounting to 206% (P < 0.001) for the high Km and 134% (P < 0.331) for the low Km 5'-NT in resistant cells. The high Km 5'-NT is probably responsible for the decreased amount of the active metabolite CdA 5'-triphosphate [40% decreased (P < 0.045)], as well as for other purine ribonucleosides and deoxyribonucleosides triphosphates in the resistant cells. In contrast, a significantly higher deoxycytidine triphosphate (dCTP) level (167%, P < 0.001) was observed in the resistant cells. Thus, this study suggests that the major cause of resistance to the nucleoside analogues CdA and ara-C in cells selected for resistance to VP is a result of metabolic alterations producing increased activity of 5'-NT and higher dCTP levels. Furthermore, these results indicate that there is a common factor in the regulation of nucleotide-degrading enzymes and DNA topoisomerases, which may be altered in cross-resistant cells.
authors.affiliation: Department of Medicine and Care, Clinical Pharmacology, Faculty of Health Sciences, Linköping, Sweden. koulo@imv.liu.se
authors.forename: K
authors.initials: K
authors.lastname: Lotfi
authors.forename: E
authors.initials: E
authors.lastname: Månsson
authors.forename: J
authors.initials: J
authors.lastname: Chandra
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: D
authors.initials: D
authors.lastname: Xu
authors.forename: E
authors.initials: E
authors.lastname: Knaust
authors.forename: T
authors.initials: T
authors.lastname: Spasokoukotskaja
authors.forename: E
authors.initials: E
authors.lastname: Liliemark
authors.forename: S
authors.initials: S
authors.lastname: Eriksson
authors.forename: F
authors.initials: F
authors.lastname: Albertioni
mesh_terms: D015720:5'-Nucleotidase / Q000378:metabolism; D015153:Blotting, Western; D002460:Cell Line; D017338:Cladribine; D003561:Cytarabine; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D003842:Deoxycytidine Kinase / Q000378:metabolism; D003845:Deoxycytosine Nucleotides / Q000378:metabolism; D004352:Drug Resistance, Microbial; D005047:Etoposide; D053222:Fas Ligand Protein; D019450:Genes, MDR; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics
chemical_list: D003845:Deoxycytosine Nucleotides; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D007527:Isoenzymes; D008562:Membrane Glycoproteins; D003561:Cytarabine; C024107:2'-deoxycytidine 5'-triphosphate; D017338:Cladribine; D005047:Etoposide; D003842:Deoxycytidine Kinase; D015720:5'-Nucleotidase; D004250:DNA Topoisomerases, Type II