Wnt/β-catenin signaling has been shown to promote self-renewal in a variety of tissue stem cells, including neuronal stem cells and hematopoietic stem cells. However, activation of the Wnt/β-catenin pathway promoted and inhibition of the pathway prevented differentiation of neuronal precursor cells. A clear explanation for the differential effects of Wnt/β-catenin activation on neuronal precursors is not available at present. Presenilin-1 (PS-1) is a polytopic protein comprised of six to eight transmembrane domains. PS-1, as part of the γ-secretase complex, is required for the intramembrane proteolysis of both amyloid precursor protein (APP) and Notch. Additionally, through interactions with β-catenin, PS-1 is associated with modulation of Wnt/β-catenin signaling. A familial Alzheimer's disease-associated PS-1 mutant, PS-1(L286V), causes a dramatic increase in T cell factor (TCF)/β-catenin transcription in PC-12 cells, which prevents normal nerve growth factor (NGF)-induced neuronal differentiation and neurite outgrowth. Selective inhibition of TCF/β-catenin/cAMP-response element-binding protein (CREB)-binding protein (CBP)-mediated transcription, but not TCF/β-catenin/p300, with the recently described small molecule antagonist ICG-001 corrects these defects in neuronal differentiation, highlighting the importance of Wnt/β-catenin signaling in this process. We propose that increased TCF/β-catenin/CBP-mediated transcription, as well as a failure to switch to TCF/β-catenin/p300-mediated transcription, play an important role in decreasing neuronal differentiation.

Wnt signaling is a major driver of stemness and chemoresistance in ovarian cancer, yet the genetic drivers that stimulate its expression remain largely unknown. Unlike other cancers, mutations in the Wnt pathway are not reported in high-grade serous ovarian cancer (HGSOC). Hence, a key challenge that must be addressed to develop effective targeted therapies is to identify nonmutational drivers of Wnt activation. Using an miRNA sensor-based approach, we have identified miR-181a as a novel driver of Wnt/β-catenin signaling. miR-181ahigh primary HGSOC cells exhibited increased Wnt/β-catenin signaling, which was associated with increased stem-cell frequency and platinum resistance. Consistent with these findings, inhibition of β-catenin decreased stem-like properties in miR-181ahigh cell populations and downregulated miR-181a. The Wnt inhibitor SFRP4 was identified as a novel target of miR-181a. Overall, our results demonstrate that miR-181a is a nonmutational activator of Wnt signaling that drives stemness and chemoresistance in HGSOC, suggesting that the miR–181a–SFRP4 axis can be evaluated as a novel biomarker for β-catenin–targeted therapy in this disease. Significance: These results demonstrate that miR-181a is an activator of Wnt signaling that drives stemness and chemoresistance in HGSOC and may be targeted therapeutically in recurrent disease.

Background: Although canonical Wnt signaling is known to promote tumorigenesis in pancreatic ductal adenocarcinoma (PDAC), a cancer driven principally by mutant K-Ras, the detailed molecular mechanisms by which the Wnt effector β-catenin regulates such tumorigenesis are largely unknown. We have previously demonstrated that β-catenin’s differential usage of the Kat3 transcriptional coactivator cyclic AMP-response element binding protein-binding protein (CBP) over its highly homologous coactivator p300 increases self-renewal and suppresses differentiation in other types of cancer. Aim/methods: To investigate Wnt-mediated carcinogenesis in PDAC, we have used the specific small molecule CBP/β-catenin antagonist, ICG-001, which our lab identified and has extensively characterized, to examine its effects in human pancreatic cancer cells and in both an orthotopic mouse model and a human patient-derived xenograft (PDX) model of PDAC. Results/conclusion: We report for the first time that K-Ras activation increases the CBP/β-catenin interaction in pancreatic cancer; and that ICG-001 specific antagonism of the CBP/β-catenin interaction sensitizes pancreatic cancer cells and tumors to gemcitabine treatment. These effects were associated with increases in the expression of let-7a microRNA; suppression of K-Ras and survivin; and the elimination of drug-resistant cancer stem/tumor-initiating cells.

Background: Triple negative breast cancers (TNBCs) are an aggressive BC subtype, characterized by high rates of drug resistance and a high proportion of cancer stem cells (CSC). CSCs are thought to be responsible for tumor initiation and drug resistance. cAMP-response element-binding (CREB) binding protein (CREBBP or CBP) has been implicated in CSC biology and may provide a novel therapeutic target in TNBC. Methods: RNA Seq pre- and post treatment with the CBP-binding small molecule ICG-001 was used to characterize CBP-driven gene expression in TNBC cells. In vitro and in vivo TNBC models were used to determine the therapeutic effect of CBP inhibition via ICG-001. Tissue microarrays (TMAs) were used to investigate the potential of CBP and associated proteins as biomarkers in TNBC. Results: The CBP/ß-catenin/FOXM1 transcriptional complex drives gene expression in TNBC and is associated with increased CSC numbers, drug resistance and poor survival outcome. Targeting of CBP/β-catenin/FOXM1 with ICG-001 eliminated CSCs and sensitized TNBC tumors to chemotherapy. Immunohistochemistry of TMAs demonstrated a significant correlation between FOXM1 expression and TNBC subtype. Conclusion: CBP/β-catenin/FOXM1 transcriptional activity plays an important role in TNBC drug resistance and CSC phenotype. CBP/β-catenin/FOXM1 provides a molecular target for precision therapy in triple negative breast cancer and could form a rationale for potential clinical trials.

Successfully targeting aberrant Wnt signaling in cancer, and even more so in chronic diseases, requires a fine balancing act, wherein the ‘dark side’ of Wnt signaling in disease can be abrogated without interfering with the crucial roles of Wnt signaling in normal tissue homeostasis and repair. Our identification of small molecule CBP/β-Catenin antagonists revealed (a) the distinctive roles that the Kat3 coactivators CBP and p300 play in Wnt signaling and orchestrating critical cellular decisions, and (b) their therapeutic potential.