The combination of IFNwith the HDACI SAHA, already in clinical use, also exerted this co operative anti cancer effects, with little effect on nor mal cells. The combination of IFNwith another HDACI, VPA, was less effective than IFNand TSA, but more effec tive than VPA and rapamycin. These results suggest that HDACI and IFNcombination therapy may be an effec tive anti cancer strategy for future clinical trials. Our data identified p21WAF1 expression as a key factor responsible for cancer cell resistance to the cytotoxic effects of combination HDACI and IFNtherapy. While IFNcan both induce or suppress p21WAF1 gene transcrip tion in different cells, it is the most common tran scriptional target of HDACIs. Previous literature suggested that up regulation of p21WAF1 by HDACIs may mediate HDACI induced cell cycle arrest and growth inhibition.

However, recent publications have cast doubt on the role of p21WAF1 in the action of HDACIs, and, conversely demonstrated that inducible p21WAF1 reduced HDACI induced cell death. Our data suggests p21WAF1 expression in some cancer Inhibitors,Modulators,Libraries cells acts as a resistance factor for the cytotoxic effects of TSA and IFNcombination therapy. The individual effects of HDACIs and IFNon angiogen esis predict a co operative therapeutic role in blocking tumour angiogenesis. Expression of HDACs is often up regulated under angiogenic stimuli such as hypoxia in cancer cells, and HDACIs can suppress HIF1expression and its Inhibitors,Modulators,Libraries down stream targets, including VEGF. HDA CIs have been recently demonstrated to inhibit endothe lial cell migration, Inhibitors,Modulators,Libraries invasion, vascular sprouting in vitro, and vasculature formation in animal models of cancer.

IFNcan repress VEGF and MMP 9 gene expression, endothelial cell functions, and, inhibit tumour driven Inhibitors,Modulators,Libraries angiogenesis in vivo. In our endothelial Inhibitors,Modulators,Libraries cell migration experiments, we found in con trast, that either TSA or IFNalone stimulated migration. We cannot fully explain the discrepancy between our data and previously published migration assays, however, this may be due to different characteristics of the migra tion chamber used. Importantly, the combination of HDACI and IFNsuppressed all endothelial cell func tions, indicating a possible role for this drug combination as a therapy for cancer patients at the point of minimal residual disease.

Conclusion In summary, we have found that the combination of HDACIs, TSA, SAHA and VPA, with IFNhave significant cytotoxic effects on a wide variety of cancer cells, with lit tle toxicity to normal non malignant cells. Inhibition of p21WAF1 expression sensitizes p21WAF1 expressing cancer cells to the combination therapy. selleck chemical Y-27632 Furthermore, HDACI and IFNco operatively suppress pro angiogenic gene expression in cancer cells, multiple endothelial cell func tions in vitro, and tumour driven vasculature formation in vivo. Our results provide a basis for further in vivo studies and eventual clinical trials using the combination of HDACIs and IFN.