The specificity of CTBP dehydrogenase inhibitors MTOB and 4-Cl-HIPP

C-terminal binding proteins (CTBPs) are conserved transcriptional repressors important in cancer and inflammation. Uniquely amongst transcriptional co-regulators, CTBPs possess a functional dehydrogenase domain. Since multiple malignancies display elevated CTBP levels, CTBP inhibitors targeting this dehydrogenase domain have been developed. While the importance of CTBPs dehydrogenase function for transcriptional regulation remains unclear, several studies have relied on CTBP inhibitors. <i>In vitro</i> experiments have confirmed binding of these compounds to CTBP's active site, however evidence for specificity is lacking. To address this, we treated wildtype and <i>Ctbp1</i> , <i>2</i> double knockout J774.1 cells with MTOB or 4-Cl-HIPP and performed RNA-seq. We observed that both inhibitors elicit distinct transcriptional changes indicating non-overlapping modes of action. Moreover, the majority of changes induced by either inhibitor are observed in <i>Ctbp1/2</i> double knockout cells suggesting off-target effects. We hypothesize that those CTBP dehydrogenase inhibitors lack specificity to CTBPs and emphasise careful revaluation of findings inferred from studies using those inhibitors.