Mechanisms of resistance to 5-aza-2′-deoxycytidine in human cancer cell lines

Abstract

5-aza-2-deoxycytidine (DAC) is approved for the treatment of myelodysplastic syndromes, but resistance to this agent is common. In search for mechanisms of resistance, we measured the half maximal (50%) inhibitory concentration (IC 50 ) of DAC and found it differed 1000-fold among a panel of cancer cell lines. The IC 50 was correlated with the doses of DAC that induced the most hypomethylation of long interspersed nuclear elements (LINE; R ‫؍‬ 0.94, P < .001), but not with LINE methylation or DNA methyltransferase 1 (DNMT1), 3a, and 3b expression at baseline. Sensitivity to DAC showed a low correlation (R ‫؍‬ 0.44, P ‫؍‬ .11) to that of 5-azacytidine (AZA), but a good correlation to that of cytarabine (Ara-C; R ‫؍‬ 0.89, P < .001). The 5 cell lines most resistant to DAC had a combination of low dCK, hENT1, and 2 transporters, and high cytosine deaminase. In an HL60 clone, resistance to DAC could be rapidly induced by drug exposure and was related to a switch from heterozygous to homozygous mutation of DCK. Transfection of wild-type DCK restored DAC sensitivity. DAC induced DNA breaks as evidenced by H2AX phosphorylation and increased homologous recombination rates by 7-to 10-fold. These results suggest that in vitro resistance to DAC can be explained by insufficient incorporation into DNA. (Blood. 2009;113:659-667)

Epigenetic cancer therapy: rationales, targets and drugs

“…This was confirmed by the selection and characterization of decitabine-resistant rat leukemic cell lines that revealed mutations in the dCyd kinase gene (Stegmann et al, 1995). Similar results were obtained in more recent studies with human cancer cells, where decitabine sensitivity could be restored by transfection of the wild-type dCyd kinase (Qin et al, 2009). dCyd kinase has also been used to predict in vivo sensitivity and resistance to other cytidine analogs, such as gemcitabine and cytarabine, in patients (Flasshove et al, 1994;Kroep et al, 2002).…”

“…Gene expression analyses that demonstrated a positive correlation between hENT1 expression and 5-azacytidine potency in human cancer cell lines provided a first indication for an important role of hENTs in 5-azacytidine uptake (Huang et al, 2004). Furthermore, low expression levels of hENT1 and hENT2 were detected in cells resistant to decitabine (Qin et al, 2009). As hENT transporters show ubiquitous expression, they can have a major role in the sensitivity and resistance of cancer cells to azanucleoside DNMT inhibitors.…”

Lack of cross‐resistance to FF‐10501, an inhibitor of inosine‐5′‐monophosphate dehydrogenase, in azacitidine‐resistant cell lines selected from SKM‐1 and MOLM‐13 leukemia cell lines

“…2014), and loss of DCK function was also reported in decitabine‐resistant cells (Qin et al. 2009). To characterize the mechanisms of azacitidine resistance, protein expression of UCK2, one of the enzymes to activate azacitidine, and DCK, an enzyme to activate decitabine, was measured in four cell lines.…”

“…Loss of DCK function is reported to be one of the mechanisms of decitabine resistance (Qin et al. 2009, 2011). Unexpectedly, the expression levels of DCK in the azacitidine‐resistant cells in the present study were not changed, although those azacitidine‐resistant cells showed strong cross‐resistance to decitabine.…”

“…2014) and deoxycytidine kinase (DCK) (Qin et al. 2009, 2011) are responsible for the resistance of azacitidine and decitabine, respectively, as the UCKs and the DCK are required for the HMAs to form their phosphorylated active metabolites. These metabolic changes observed in HMA resistance may have an impact on the efficacies of other antimetabolic agents, such as cytarabine, for the treatment of AML, that is, a possible risk of cross‐resistance in the treatment of MDS and/or AML.…”