NSM00158 Specifically Disrupts the CtBP2-p300 Interaction to Reverse CtBP2-Mediated Transrepression and Prevent the Occurrence of Nonunion

The transrepression and transactivation roles of CtBPs in the pathogenesis of different diseases

Gene transcription is strictly controlled by transcriptional complexes, which are assemblies of transcription factors, transcriptional regulators, and co-regulators. Mammalian genomes encode two C-terminal-binding proteins (CtBPs), CtBP1 and CtBP2, which are both well-known transcriptional corepressors of oncogenic processes. Their overexpression in tumors is associated with malignant behavior, such as uncontrolled cell proliferation, migration, and invasion, as well as with an increase in the epithelial-mesenchymal transition. CtBPs coordinate with other transcriptional regulators, such as histone deacetylases (HDACs) and histone acetyltransferases (p300 and CBP [CREBP-binding protein]) that contain the PXDLS motif, and with transcription factors to assemble transcriptional complexes that dock onto the promoters of genes to initiate gene transcription. Emerging evidence suggests that CtBPs function as both corepressors and coactivators in different biological processes ranging from apoptosis to inflammation and osteogenesis. Therapeutic targeting of CtBPs or the interactions required to form transcriptional complexes has also shown promising effects in preventing disease progression. This review summarizes the most recent progress in the study of CtBP functions and therapeutic inhibitors in different biological processes. This knowledge may enable a better understanding of the complexity of the roles of CtBPs, while providing new insights into therapeutic strategies that target CtBPs.

A naturally derived small molecule PSM0537 targets the AF1Q-TCF4 interaction to suppress COX2 expression and inhibit cell proliferation and metastasis in osteosarcoma

ALL1 fused gene from chromosome 1q (AF1Q) functions as an oncogene in several types of cancers, but it has not been observed in osteosarcoma. In this study, we revealed that AF1Q was overexpressed in multiple osteosarcoma cell lines, and its expression level increased with the severity of tumor malignancy in osteosarcoma biopsies. AF1Q was coupled with the transcription factor T cell factor 4 (TCF4) to assemble a complex to bind to the promoter of cyclooxygenase 2 (COX2) and activate its expression. The individual knockdown of AF1Q, TCF4, or COX2 in osteosarcoma cell lines significantly decreased cell proliferation and invasion in vitro. The tumor xenograft model also indicated that the individual knockdown of AF1Q, TCF4, or COX2 could inhibit tumor growth and metastasis. On the basis of these promising results, we established an in vitro AlphaScreen method to identify the compounds that disrupted the AF1Q-TCF4 interaction in a naturally derived small molecule pool. We discovered a compound called PSM0537, which showed a strong ability to inhibit the AF1Q-TCF4 interaction at a low dose of half-maximal inhibitory concentration (IC₅₀) (210.3 ± 15.6 nM). The administration of PSM0537 in vitro and in vivo could dramatically inhibit cell proliferation, invasion, and metastasis. Collectively, our findings reveal that the AF1Q-TCF4 transcriptional complex controls the expression of COX2 and that targeting the AF1Q-TCF4 interaction with PSM0537 could inhibit tumor cell growth and metastasis. Our results provide a new path for chemotherapy of osteosarcoma.

Targeting the CtBP1-FOXM1 transcriptional complex with small molecules to overcome MDR1-mediated chemoresistance in osteosarcoma cancer stem cells

Chemoresistance is a major barrier for the chemotherapy of osteosarcoma. The induction of multidrug resistance protein 1 (MDR1), an ATP-dependent transporter, can efflux anti-cancer drugs, thereby decreasing chemosensitivity. However, an actual involvement of MDR1 in the chemoresistance of osteosarcoma cells has not been established. We obtained two cisplatin (CDDP)-resistant osteosarcoma cancer stem cell (CSC) lines using sphere formation medium supplemented with CDDP. These two CDDP-resistant CSC cell lines showed substantial cell proliferation, colony formation, cell invasion, and in vivo tumor growth in the presence of CDDP. Microarray analysis revealed that three genes, MDR1, FOXM1 (forkhead box M1), and CtBP1 (C-Terminal binding protein 1), showed significant overexpression in both cell lines. Mechanistically, CtBP1 assembled with FOXM1 to form a transcriptional complex, which docked onto the MDR1 promoter to activate MDR1 expression. Knockdown or inhibition of the CtBP1-FOXM1 components with specific small molecules, including NSM00158 and NSC95397 for CtBP1 and RCM1 for FOXM1, significantly repressed MDR1 expression. Administration of these three small molecules also significantly inhibited tumor growth in mouse tumor xenograft model. The MDR1-mediated chemoresistance could be reversed by NSM00158 and RCM1. Collectively, our data revealed that the CtBP1-FOXM1 complex activated MDR1 expression and that targeting this complex with their specific inhibitors could reverse MDR1-mediated chemoresistance both in vitro and in vivo. Our results indicate a new therapeutic strategy for overcoming chemoresistance during osteosarcoma treatment.