Pharmacokinetic data from clinical trials following a twice daily dose of vorinostat determined that src inhibitor dasatinib the half life was in the range of 1 3. 5 h and maximal serum concentrations did not peak over 2 M and rapidly diminished. Of note, the half life of LBH589 was determined to be in the order of 10 14 h and serum concentrations of 400 700 nM are achievable at doses which are well tolerated. There fore, the concentration of LBH589 required to achieve 50% growth inhibition in our colon cancer cells was well within clinically achievable concentrations whereas the concentration of vorinostat was within, but approaching the upper limit of reported serum concentration ranges. The cDNA microarray analysis demonstrated that in each cell line that the gene expression profile was significantly altered after a 24 h exposure to either HDAC inhibitor, vorinostat or LBH589.

Considering the mechanism of action of HDACi including histone acetyla tion induced chromatin remodeling and the acetylation of non histone proteins including transcription factors, it is intriguing that only 5 7% of genes in the colon cancer cell lines analyzed were modulated by HDACi treatment. However, our results are consistent with other microarray profiling experiments which reported as few as 2% and as high as 10% modulated by HDACi. These reports and the data presented herein would indicate that HDACi do not induce global gene expression changes and may instead target specific sets of genes. An important observation in this study was that vorinostat and LBH589 induced very similar transcriptional profiles within each cell line.

As both of these agents are hydroxamate Anacetrapib class HDACi, this observation is somewhat expected. Additional studies have identified very similar transcriptional changes pro duced by the two hydroxamic acid based HDACi, TSA and vorinostat, while also demonstrating a different gene expression profile obtained with the benzamide class HDACi MS 275. The analysis of our data demonstrates that HDACi induce significant cell line specific effects on genes involved in the regulation of a number of critical tumor processes including angiogenesis, mitosis, DNA replication, recom bination and repair and apoptosis. More specifically, the potent anti angiogenic matrix glycoprotein throm bospondin 1, was significantly upregulated 14 fold in HCT116 cells at 24 h. HT29 cells how ever, showed no modulation until 24 h post treatment where only a modest increase of 2 fold was observed by qPCR. HDACi are reported selleckchem to be potent inhibitors of tumor angiogenesis and induction of THBS1 has previ ously been reported following HDAC inhibition.