Histone deacetylase inhibitors suppress inducibility of nuclear factor-κB by tumor necrosis factor-α receptor-1 downregulation

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Recently, the inhibition of histone deacetylase (HDAC) enzymes has attracted attention in the oncology community as a new therapeutic opportunity for haematological and solid tumors including non-small cell lung cancer (NSCLC) and several clinical phase I investigations are underway for compounds, such as SAHA and MS275. Moreover, in haematological malignancies, such as diffuse large B-cell lymphoma, SAHA has advanced to phase II and III evaluation. Albeit their apparent anti-tumor efficacy, the mechanism of action of HDAC inhibitors remains far from conclusively understood. We investigated a possible impact of HDAC inhibition on the functionality of the nuclear factor-κB (NF-κB) pathway in NSCLC cell lines. In tumors, this transcription factor plays a pivotal role in the control of pro- and anti-apoptotic stimuli, and interference with its activity could rationalize a possible therapeutic benefit. We found, that in the NSCLC cell lines A549 and NCI-H460, the NF-κB pathway was not in a constitutively active state, but fully inducible, for example by stimulation with tumor necrosis factor-α (TNF-α). Incubation of NSCLC cells with HDAC inhibitors (HDI), however, greatly reduced responsiveness of the pathway to TNF-α stimulation. We observed, that incubation with HDI led to drastically lowered expression of TNF-α receptor 1 (TNFR1) mRNA as well as TNFR1 protein levels. Accordingly, exposure of the receptor at the cell surface was almost completely absent, and HDI treated cells responded to TNF-α treatment with reduced IKK phosphorylation and activation, delayed IκB-α phosphorylation, and attenuated NF-κB nuclear translocation and DNA binding. In consequence, stimulation of NF-κB target gene expression by TNF-α was strongly decreased.This indicates the possibility, that beyond their directly cytotoxic effect on tumor cells, HDI might be beneficial for tumor treatment by reducing the responsiveness of tumor cells to the TNF-α mediated activation of the NF-κB pathway, mainly brought about by stromal cells. The findings also might hint at a possible use of HDI in inflammatory diseases, which are associated with overproduction of TNF-α, such as rheumatoid arthritis or Crohn’s disease.