Protocatechuic Aldehyde Represses Proliferation and Migration of Breast Cancer Cells through Targeting C-terminal Binding Protein 1

PURPOSE: C-terminal binding protein 1 (CtBP1) is a transcriptional co-repressor that is overexpressed in many cancers. CtBP1 transcriptionally represses a broad array of tumor suppressors, which promotes cancer cell proliferation, migration, invasion, and resistance to apoptosis. Recent studies have demonstrated that CtBP1 is a potential target for cancer therapy. This study was designed to screen for compounds that potentially target CtBP1. METHODS: Using a structure-based virtual screening for CtBP1 inhibitors, we found protocatechuic aldehyde (PA), a natural compound found in the root of a traditional Chinese herb, Salvia miltiorrhiza, that directly binds to CtBP1. Microscale thermophoresis assay was performed to determine whether PA and CtBP1 directly bind to each other. Further, clustered regularly interspaced short palindromic repeats associated Cas9 nuclease-mediated CtBP1 knockout in breast cancer cells was used to validate the CtBP1 targeting specificity of PA. RESULTS: Functional studies showed that PA repressed the proliferation and migration of breast cancer cells. Furthermore, PA elevated the expression of the downstream targets of CtBP1, p21 and E-cadherin, and decreased CtBP1 binding affinity for the promoter regions of p21 and E-cadherin in breast cancer cells. However, PA did not affect the expression of p21 and E-cadherin in the CtBP1 knockout breast cancer cells. In addition, the CtBP1 knockout breast cancer cells showed resistance to PA-induced repression of proliferation and migration. CONCLUSION: Our findings demonstrated that PA directly bound to CtBP1 and inhibited the growth and migration of breast cancer cells through CtBP1 inhibition. Structural modifications of PA are further required to enhance its binding affinity and selectivity for CtBP1.