combinations in HCT116 and HT29 tumour xenografts HCT116 tumour bearing mice were treated as described in the methods section with PXD101 and 5 FU . At these concentrations Tasocitinib each compound alone produced reductions in tumour volume over the measured period . When PXD101 and 5 FU were administered together there was a further inhibition of tumour growth, with a signiWcant reduction in volume at days 28 and 31 compared to the single compound treated groups . At day 24, there was a signiWcant reduction in tumour growth with co administration compared to 5 FU alone only. No signiWcant eVect on body weight was observed for any of the treated groups . In a subsequent xenograft experiment, using HT29 cells, the dose of 5 FU was increased to 30 mg/kg in an attempt to achieve an enhanced eVect over that found using 15 mg/kg 5 FU in the HCT116 study.
Only one cycle, however, of 5 FU treatment was administered at this level due to toxicity. The combination of 100 raltegravir molecular weight mg/ kg PXD101 with 30 mg/kg produced four mice with toxic weight loss, two of which subsequently died. This group was, therefore, excluded from subsequent study. Some tumour inhibition was observed in the 60 mg/ kg PXD101 and 30 mg/kg 5 FU single treatment groups, with increased tumour growth inhibition in the PXD101/5 FU group . The eVect of the combination is larger when data is normalised to the pre treatment tumour volume , with the tumour reduction by the combination signiWcantly greater than the control and 5 FU alone groups at days 24, 28, 31 and 35. Statistical signiWcance was not achieved compared to the PXD101 alone group at any measurement time.
It should be noted that toxic weight chemical screening loss was observed in mice from both the 5 FU Dasatinib ic50 alone and in the group treated with the combination . Owing to this, the 5 FU treatment was halted after only the Wrst weekly cycle allowing body weight recovery, even though they were treated with the second cycle of PXD101. Discussion The Wnding that treatment of cell lines with HDACi in vitro, as demonstrated by others , only appears to regulate a relatively small subset of genes is surprising given the lack of HDAC isoform selectivity that most HDACi demonstrate see ref. for an overview of the classical HDAC family). Commonly included in the subset of genes that are regulated by HDACi is TS.
It has been nausea previously demonstrated that HDACi, including trichostatin A , suberoylanilide hydroxamic acid , MS275, FK228 and BL1521, can down regulate the expression of TS in vitro . Down regulation of TS is likely to be a fundamental response to histone acetylation induced by HDACi treatment since it was not found to be species or cell line/type speciWc .As discussed in the introduction, over expression of TS in colorectal cancer in vitro is implicated in the mechanism of resistance to 5 FU and is a marker of poor prognosis clinically . Therefore any reduction in TS levels in patient colorectal tumours may translate into a clinical advantage. It has been demonstrated here that PXD101, in common with other HDACi, can down regulate TS expression both at the mRNA and protein level. Similar to other HDACi, it is likely that PXD101 regulates TS levels via eVects on histone acetylation and downstream transcription. This led to the hypothesis that combining .