Gemcitabine is indicated in combination with cisplatin as first-line therapy for 
solid tumours including non-small cell lung cancer (NSCLC), bladder cancer and 
mesothelioma. Gemcitabine is an analogue of pyrimidine cytosine and functions as 
an anti-metabolite. Structurally, however, gemcitabine has similarities to 
5-aza-2-deoxycytidine (decitabine/Dacogen®), a DNA methyltransferase inhibitor 
(DNMTi). NSCLC, mesothelioma and prostate cancer cell lines were treated with 
decitabine and gemcitabine. Reactivation of epigenetically silenced genes was 
examined by RT-PCR/qPCR. DNA methyltransferase activity in nuclear extracts and 
recombinant proteins was measured using a DNA methyl-transferase assay, and 
alterations in DNA methylation status were examined using methylation-specific 
PCR (MS-PCR) and pyrosequencing. We observe a reactivation of several 
epigenetically silenced genes including GSTP1, IGFBP3 and RASSF1A. Gemcitabine 
functionally inhibited DNA methyltransferase activity in both nuclear extracts 
and recombinant proteins. Gemcitabine dramatically destabilised DNMT1 protein. 
However, DNA CpG methylation was for the most part unaffected by gemcitabine. In 
conclusion, gemcitabine both inhibits and destabilises DNA methyltransferases 
and reactivates epigenetically silenced genes having activity equivalent to 
decitabine at concentrations significantly lower than those achieved in the 
treatment of patients with solid tumours. This property may contribute to the 
anticancer activity of gemcitabine.