CBX4 acetoacetylation as an inhibitory mechanism of HIF-1α activity.

HIF-1α transcriptional activity is enhanced through SUMOylation mediated by CBX4. Despite the recognized importance of the CBX4-HIF-1α axis, the molecular mechanisms governing its regulation remain largely unclear. In this study, phenotypic screening of a 101,254-compound library followed by structural optimization led to the identification of XZA-1, a small molecule capable of disrupting CBX4-mediated HIF-1α transcriptional activation. Mechanistic investigations revealed that XZA-1 activates HADH, a key enzyme in fatty acid β-oxidation, resulting in increased intracellular levels of acetoacetyl-CoA. This metabolite promotes acetoacetylation of CBX4 at lysine 106, thereby reducing its SUMO E3 ligase activity. In a CBX4-overexpressing xenograft model, XZA-1 demonstrated antitumor effects by enhancing CBX4 K106 acetoacetylation. Additionally, elevated levels of CBX4 K106 acetoacetylation were observed in clinical HCC tissues from patients with better overall survival. These findings suggest that acetoacetyl-CoA functions as a potential antitumor metabolite and establish a novel pharmacological approach for modulating HIF-1α transcriptional activity in cancer.