Dual antitumour effect of 5-azacytidine by inducing a breakdown of resistance-mediating factors and epigenetic modulation

Abstract

BackgroundThe cytokine tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) has shown promising anticancer activity in early clinical settings by selectively inducing apoptosis in different tumour types. However, some tumour entities such as hepatocellular carcinoma (HCC) display an inherent resistance to TRAIL. A huge effort has been made to unravel strategies for a clinically applicable sensitisation of resistant cancer cells to TRAIL. Reversible epigenetic alterations such as DNA methylation play a major role in development, maintenance and resistance phenomena of tumour cells. Currently, several clinical trials are exploiting the potential of epigenetic drugs, such as 5-azacytidine (5-aza-CR) or 5-aza-2 9 -deoxycytidine (5-aza-dC) to break primary or secondary resistance phenomena of cancer cells. Therefore, 5-aza-CR and 5-aza-dC were investigated in the context of TRAIL resistance. Methods Alterations in proliferation, apoptosis, regulatory proteins and toxicity were investigated in TRAIL-resistant hepatoma, and also in renal, colon and pancreatic cancer cells as well as non-transformed human-derived primary hepatocytes, tissue slices isolated from human liver and non-malignant colon cells, all of which had been exposed to demethylating drugs and/or TRAIL. Results Within hours, 5-aza-CR but not 5-aza-dC sensitised in vitro cultured tumour cells to TRAIL, first by activating caspases, followed by a subsequent induction of apoptosis. This surprisingly rapid sensitisation was confirmed in vivo employing a chorioallantoic membrane assay. As a major mechanism, a 5-aza-CR-induced inhibition of cellular protein synthesis was found which led to a breakdown of tumour-protecting factors such as the antiapoptotic factor FLICE inhibitory protein (FLIP). Importantly, TRAIL and 5-aza-CR did not induce relevant toxicity or apoptosis in primary hepatocytes, liver slices from different human donors and in normal colon cells. Conclusions Molecular evidence is provided for a novel 5-aza-CR-based translational approach enabling a twofold treatment of apoptosis-resistant tumour entities, not only by an epigenetic reversion of the malignancy-associated phenotype but also by an efficient resensitisation to apoptosis-inducing substances such as TRAIL.

Epigenetic Impacts of Ascorbate on Human Metastatic Melanoma Cells

“…Epigenetic alterations that induce multiple changes in gene expression profiles are substantial features of cancer (88–90). Several epigenetic mechanisms have been described so far and the investigation of this complex molecular machinery is ongoing.…”

Differential Induction of Apoptosis and Senescence by the DNA Methyltransferase Inhibitors 5-Azacytidine and 5-Aza-2′-Deoxycytidine in Solid Tumor Cells

“…Unlike 5-aza-dC, 5-aza-CR is known to block RNA synthesis (3,30), followed by inhibition of protein synthesis, which might especially affect short-lived proteins, such as p53 (3,4). For this reason, the protein levels of p53 in HepG2 cells were determined by Western blotting after 5-aza-CR or 5-aza-dC treatment (Fig.…”

“…For a purposeful combination of DNMTi substances with other anticancer principles it is of utmost importance to exactly define the individual tumor cell response pattern to each distinct DNMTi compound. Although both DNMTi only minimally differ in their molecular structure, there are important differences in their molecular mode of action (3,4).…”

Hepatoepigenetic Alterations in Viral and Nonviral-Induced Hepatocellular Carcinoma

“…Combination therapy with decitabine and suberoylanilide hydroxamic acid (SAHA) significantly reduces cell growth and proliferation in a xenograft hepatoma model [157]. On the other hand, azacytidine induces apoptosis by inhibiting protein biosynthesis when used in combination with tumour necrosis factor related apoptosis inducing ligand (TRAIL) [158]. Guadecitabine is a hypomethylating agent that has been formulated as a dinucleotide antimetabolite of a decitabine that is linked to a guanosine through a phosphodiester bond.…”