Abstract #LB-168: Differences in in vitro azacitidine and decitabine activities in non-small cell lung cancer

AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO The azanucleosides 5-azacytidine (azacitidine; Vidaza; AZA) and 2\#8217;-deoxy-5-azacytidine (decitabine; Dacogen; DAC) are DNA methyltransferase (DNMT) inhibitors that have shown clinical benefit in the treatment of myelodysplastic syndromes (MDS) and are approved by the Food and Drug Administration for the treatment of MDS. While AZA has demonstrated the ability to significantly extend overall survival in MDS patients, DAC failed to show a survival benefit over conventional therapy in a similar trial. The different outcomes of these late-stage clinical studies suggest that AZA and DAC may have different modes of action. To better understand the mechanism of action of these two drugs, we examined the effects of AZA and DAC in a panel of cancer cell lines. We found that AZA and DAC differentially affected the viability of many cell lines, with the greatest difference exhibited in non-small cell lung cancer (NSCLC) cells. Of the six NSCLC lines tested, all were sensitive to AZA (EC50 of 1-6 \#956;M) while only one was sensitive to DAC (EC50 of 5 \#956;M). Both inhibitors caused DNMT1 depletion and DNA demethylation in these cells; however, only AZA induced histone-H2AX phosphorylation (a marker of DNA damage) and PARP cleavage (a marker of cell death), suggesting that mechanisms in addition to, or other than DNA hypomethylation, are important for AZA-mediated reduction of NSCLC cell viability. Consistent with these results, AZA-treated, but not DAC-treated, cells were positive for AnnexinV staining, indicative of cells undergoing apoptosis. Cell cycle analysis indicated that AZA induced an accumulation of cells in the sub-G1 phase whereas DAC mainly caused an increase of cells in G2/M. Gene expression analysis of AZA- and DAC-treated cells revealed strikingly different profiles, with many genes distinctly regulated by each drug. Collectively, these results in NSCLC cell lines suggest that besides the common activities of AZA and DAC on DNMT depletion and DNA hypomethylation, these drugs differ in other aspects, including regulation of gene expression and induction of apoptosis. Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr LB-168.