The aim of our study was to evaluate the potential of HDAC8 Blasticidin S as a therapeutic target. Overexpression of HDAC8 has been reported in a considerable number of different cancer entities [26,34,36,37]. In neuroblastoma, in particular, HDAC8 expression was significantly correlated with further poor prognostic markers as well as poor overall and progression-free survival. SiRNA-mediated knockdown and pharmacological inhibition of HDAC8 in neuroblastoma significantly decreased proliferation rate and reduced Tozasertib chemical structure clonogenic growth, cell cycle arrest, and differentiation [34]. In hepatocellular carcinoma HDAC8 knockdown also suppresses cell proliferation and enhances apoptosis via elevated
expression of p53 and acetylation of p53 at Lys382 [36]. As there were indications from our own and other data that HDAC8 is often upregulated in urothelial carcinoma as well [39,44], the question arose whether HDAC8 might be a potential target for anticancer treatment in this tumor. In urothelial cancer cell lines, a variable expression of HDAC8 was observed both at mRNA and protein level [39]. Importantly, mRNA expression levels were comparable to neuroblastoma and breast cancer cells (data not find more shown). An according variability has also been reported
from investigations in further malignomas, e.g. hepatocellular carcinoma cell lines, were also a broad range of HDAC8 expression was observed in cancer cell lines [36]. Differences between mRNA and protein expression indicate that HDAC8 expression and activity in UCCs may be regulated both transcriptionally and on the protein level, e.g. by protein kinase A (PKA) phosphorylation [30,31]. In addition, in our UCC panel, a low HDAC8 expression was predominantly observed in UCCs with an epithelial Aldehyde dehydrogenase phenotype. Therefore, to cover this range both on protein and mRNA
level, we chose to apply a panel of 6 cell lines representing the heterogeneity of the HDAC8 expression instead of focusing on one urothelial cancer cell line. SiRNA targeting of HDAC8 in UCCs caused a significant reduction of proliferation up to 45% and inhibited clonogenic growth in a cell line-dependent manner. These results were comparable to observations in hepatocellular carcinoma (HCC) and neuroblastoma cells [34,36]. Clonogenic growth was most decreased in the mesenchymal cell line SW-1710 which presented the highest HDAC8 protein expression. Treatment with the three different HDAC8 inhibitors c2, c5 and c6 revealed a low sensitivity of UCCs for c2 with a calculated IC50 value greater than 50 μM. In contrast, neuroblastoma cell lines (BE (2)-C) were more sensitive to treatment with c2, presenting IC50 values in a range of 10 to 40 μM. In these cells, the HDAC8 inhibitor c2 yielded an similar phenotype at a concentration similar to the in vitro IC50 of c2 against HDAC8 [41].