title: Induction of resistance to the lipophilic cytarabine prodrug elacytarabine (CP-4055) in CEM leukemic cells.
abstract: The deoxynucleoside analogs cytarabine (Ara-C) and gemcitabine (dFdC) are widely used in the treatment of cancer. Due to their hydrophilic nature they need the equilibrative (hENT) and concentrative (hCNT) nucleoside transporters to enter the cell. To bypass drug resistance due to decreased uptake, lipophilic 5'elaidic acid esters were synthesized, elacytarabine (CP-4055, from ara-C) and CP-4126 (from gemcitabine), which are currently in clinical development for solid and hematological tumors. We investigated whether resistance can be induced in vitro, and treated the CEM leukemic cell line with weekly increasing elacytarabine concentrations, up to 0.28 microM (10 times IC(50)). The IC(50) of the resistant CEM/CP-4055 was 35 microM, about 1,000 times that of the wildtype CEM, and comparable to that of CEM/dCK- (deoxycytidine kinase deficient) (22 microM). CEM/CP-4055 was also cross-resistant to Ara-C, gemcitabine and CP-4126 (28 and 33 microM, respectively). A low level of mRNA dCK was observed, and similar to CEM/dCK-, CEM/CP-4055 did not accumulate Ara-CTP after exposure to Ara-C or elacytarabine, which is consistent with a deficiency in dCK. In conclusion, elacytarabine induced resistance similar to Ara-C. This resistance was caused by downregulation of dCK.
authors.affiliation: Department of Medical Oncology, VU University Medical Center, Amsterdam, the Netherlands.
authors.forename: A D
authors.initials: AD
authors.lastname: Adema
authors.forename: N
authors.initials: N
authors.lastname: Losekoot
authors.forename: K
authors.initials: K
authors.lastname: Smid
authors.forename: I
authors.initials: I
authors.lastname: Kathmann
authors.forename: F
authors.initials: F
authors.lastname: Myhren
authors.forename: M L
authors.initials: ML
authors.lastname: Sandvold
authors.forename: G J
authors.initials: GJ
authors.lastname: Peters
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D003561:Cytarabine / Q000031:analogs & derivatives* / Q000494:pharmacology; D003564:Cytidine Deaminase; D003841:Deoxycytidine / Q000031:analogs & derivatives / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D006801:Humans; D007938:Leukemia / Q000201:enzymology / Q000235:genetics; D009700:Nucleoside Deaminases / Q000235:genetics / Q000502:physiology; D016133:Polymerase Chain Reaction; D000093542:Gemcitabine
chemical_list: D000970:Antineoplastic Agents; D003561:Cytarabine; D003841:Deoxycytidine; C047645:5'-oleoyl cytarabine; D009700:Nucleoside Deaminases; D003564:Cytidine Deaminase; C011530:deoxycytidine deaminase; D000093542:Gemcitabine