feration and cell cycle distributions was assessed with the sulforhodamine B assay and flow cytometry, respectively, as previously described . Cell treatment for in vitro MRS PC3 and HT29 cells were treated for 24 hours with belinostat , to obtain TGF-beta a 30% to 50% reduction in cell counts and induction of histone 3 acetylation as a characteristic molecular biomarker of HDAC inhibition . HT29 cells were further treated with 2 mmol/L belinostat for 4 and 16 hours to assess response time dynamics. Control cells were treated with 0.01% dimethyl sulfoxide . For 13C tracer experiments, HT29 cells were treated as above for 16 hours followed by a further 3 hour incubation in fresh medium containing DMSO or 2 mmol/L belinostat and 28 mmol/L choline or 5 mmol/L glucose .
At the end of treatment, cells were extracted with a dualphase method and samples lyophilized for MRS analysis. Quantitative real time PCR Total RNA meropenem was extracted with the RNAeasy Kit , and 500 ng was reverse transcribed with the High Capacity cDNA Reverse Transcription Kit . Samples were diluted 1:5, and 1 mL used in the Taqman assay, using Taqman universal master mix, and the Hs03682798_m1 assay for the ChoKa gene CHKA multiplexed with the 4326314E assay for large ribosomal protein 0 gene LRP0 . mRNA levels of CHKA and LRP0 were determined for each sample in the same well on the ABI 7900HT. CHKA mRNA levels were expressed relative to those of LRP0. HT29 human colon tumor xenograft model HDAC inhibitors are targeted anticancer agents currently approved for cutaneous T cell lymphoma and in mid late stage trials for other cancers .
The development of such agents requires the discovery and validation of biomarkers, and particularly those that are noninvasive, to monitor target modulation and aid treatment planning and evaluation. Imaging of tumor metabolism is a promising approach for surgery biomarker discovery as it exploits the distinct metabolic characteristics of the tumor to inform on its behavior following therapy . Moreover, studying tumor metabolism informs on the metabolic pathways modulated by targeted agents thereby providing a means for investigating potential mechanisms of action. Using MRS, we have previously shown that HDAC inhibition with LAQ824 leads to increased PC levels in HT29 human colon carcinoma cells in vitro and tumors in vivo .
The aims of this study were to confirm this observation with belinostat in HT29 cells in vitro and in vivo in addition to PC3 human prostate cancer cells in vitro and investigate the mechanism underlying this effect. The clinical development of belinostat is now primarily directed toward the use of this drug in combination with chemotherapy. In this study, belinostat served as an alternative chemotype probe to the agents currently in the clinic. Probe compounds have considerable value for interrogating the molecular function of target proteins and the downstream biological processes they mediate, and for biomarker discovery and validation . HT29 and PC3 cells were treated in vitro with belinostat at a concentration and duration that led to target modulation and inhibition of cell proliferation . 31PMRS metabolic analysis under these conditions indicated that the most significant effect observed in both HT29 and PC3 cells after 24 hours.