The Hdac Inhibitor Belinostat Downregulates Survivin In The Fet Colon Cancer Cell Line By A Tgf#946, Signaling Dependent Mechanism

Survivin is a member of the IAP family and is ubiquitously expressed in tumor cells. This \#8220;cancer specific\#8221; gene also functions to promote angiogenesis, cell division and is a marker of poor prognosis. Histone deacetylase inhibitors (HDACi) induce apoptosis and re-expression of epigenetically silenced tumor suppressor genes (TSG) in cancer cells. In association with increased expression of the TSG transforming growth factor \#946; receptor II (TGFsRII) induced by the HDACi belinostat, we have observed decreased survivin expression. HDACi are in clinical trial. Identification of the targets and molecular mechanisms involved in their effects will identify both the therapeutically important HDAC\#8217;s and the most effective combination therapies. Therefore, we are currently investigating the molecular mechanisms involved in survivin downregulation by the HDACi belinostat in the FET colon carcinoma cell line. We have identified two mechanisms involved in the belinostat induced repression of survivin. Firstly, at early time points following belinostat treatment (0-4h), the survivin protein half life is significantly decreased. The proteasome is involved in this increased degradation as determined by the use of MG132 and lactacystin. Significantly, the decrease in survivin half life is delayed in FET cells stably transfected with dominant negative TGFsRII. Secondly, at late time points (24-72h) following treatment with belinostat, the level of survivin mRNA is decreased. The transcriptional activity of the survivin promoter construct p1430-luciferase stably transfected into FET cells is similarly decreased 48h post treatment. This suppression of transcriptional activity by belinostat also demonstrates some dependence on TGF\#946; signaling. At pharmacologically low doses of belinostat, blocking the TGF\#946; pathway by the ALK5i inhibitor or using FET cells stably transfected with dominant negative TGFsRII partially rescued survivin transcription. We also treated FET Smad 2 knockdown cells with belinostat and found that survivin downregulation by belinostat was partially rescued. DNA fragmentation assay revealed that belinostat induced cell death is through the activation of caspase 3 and 9 and blocking the TGF\#946; pathway reduced cell death. Similar results were obtained with the HDACi trichostatin A. Belinostat also induced expression of epigenetically silenced TGFsRII in the MCF7L breast cancer cell line which resulted in TGF\#946; mediated survivin repression. Therefore, induction of TGFsRII with concomitant survivin repression may represent significant mechanisms in the anti-cancer effects of this drug. Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr LB-209.