Cellular Resistance Against Troxacitabine in Human Cell Lines and Pediatric Patient Acute Myeloid Leukemia Blast Cells

Abstract

Troxacitabine is a cytotoxic deoxycytidine analogue with an unnatural L-configuration, which is activated by deoxycytidine kinase (dCK). The configuration is responsible for differences in the uptake and metabolism of troxacitabine compared to other deoxynucleoside analogues. To determine whether troxacitabine has an advantage over other nucleoside analogues several cell lines resistant to cladribine and gemcitabine were exposed to troxacitabine, while blast cells from pediatric leukemia patients were tested for cross-resistance with other deoxynucleoside analogues. The gemcitabine resistant AG6000 (IC50: >3000 nM), and the cladribine resistant CEM (IC50: 150 nM) and HL-60 (IC50: >3000 nM) cell lines, all with no or decreased dCK expression, were less sensitive to troxacitabine than their wild type counterparts (IC50; A2780: 410, CEM: 71 and HL-60: 158 nM). dCK protein expression in CEM was higher than in HL-60, which, in turn, was higher than in A2780. Catalytically inactive p53 seems to increase the sensitivity to troxacitabine. The patient samples showed a large range of sensitivity to troxacitabine, similar to other deoxynucleoside analogues. Cross-resistance with all other deoxynucleoside analogues was observed.

Metabolism, Biochemical Actions, and Chemical Synthesis of Anticancer Nucleosides, Nucleotides, and Base Analogs

“…However, removal of the incorporated troxacitabine-5′-monophosphate from DNA can occur by the APE-1 excision repair mechanism . Resistance to troxacitabine 48 exposure can arise by decreased expression of 2′-deoxycytidine kinase in vitro …”

“…Troxacitabine 48 initially showed promising anticancer activity against solid tumors and leukemias. ,,− Tumor cells with catalytically inactive p53 have increased sensitivity to troxacitabine 48 exposure . In addition, pancreatic cell lines were shown to have increased sensitivity to troxacitabine prodrugs bearing N 4 single carbon chain amides to increase drug lipophilicity .…”

“…Clofarabine 12 is usually administered intravenously; however, the increased stability of the glycosidic bond also allows for oral administration. ,, Clofarabine 12 enters the cell via hENT1, hENT2, and hCNT2, and to a much lesser extent by passive diffusion . 2′-Deoxycytidine kinase generates clofarabine-5′-monophosphate; however, the enzyme has a lower K m for clofarabine 12 than cladribine 8 .…”

“…The negatively charged fludarabine-5′-monophosphate 7 is dephosphorylated in the plasma by ecto-5′-nucleotidase, and fludarabine 291 is transported into cells by nucleoside transporters hENT1, hENT2, and hCNT3. , Although fludarabine-5′-monophosphate 7 is adenosine deaminase resistant, the drug is susceptible to glycosidic bond cleavage, which results in the formation of 2-fluoroadenine, a precursor to the toxic 2-fluoroadenosine-5′-triphosphate (see section ). After entering the cell, fludarabine 291 is initially phosphorylated by cellular 2′-deoxycytidine kinase, although it is a relatively poor substrate for the enzyme. , Deoxyguanosine kinase has also been reported to phosphorylate fludarabine .…”

Anti proliferative activity of ELACYT™ (CP-4055) in combination with cloretazine (VNP40101M), idarubicin, gemcitabine, irinotecan and topotecan in human leukemia and lymphoma cells

“…The 20-fold difference in sensitivity in HL-60 versus U937 to both drugs was notable. The relative resistance of HL-60 cells was not due to lack of immunoreactive deoxycytidine kinase in this cell line [ 28 ], however other metabolic factors could be involved, including 5′-nucleotidase, cytidine deaminase and DNA polymerase [ 2 ].…”