Wnt/ß-Catenin Small-Molecule Inhibitor CWP232228 Preferentially Inhibits the Growth of Breast Cancer Stem-like Cells.

Breast cancer stem cells (BCSC) are resistant to conventional chemotherapy and radiotherapy, which may destroy tumor masses but not all BCSC that can mediate relapses. In the present study, we showed that the level of Wnt/ß-catenin signaling in BCSC is relatively higher than in bulk tumor cells, contributing to a relatively higher level of therapeutic resistance. We designed a highly potent small-molecule inhibitor, CWP232228, which antagonizes binding of ß-catenin to T-cell factor (TCF) in the nucleus. Notably, although CWP232228 inhibited the growth of both BCSC and bulk tumor cells by inhibiting ß-catenin-mediated transcription, BCSC exhibited greater growth inhibition than bulk tumor cells. We also documented evidence of greater insulin-like growth factor-I (IGF-I) expression by BCSC than by bulk tumor cells and that CWP232228 attenuated IGF-I-mediated BCSC functions. These results suggested that the inhibitory effect of CWP232228 on BCSC growth might be achieved through the disruption of IGF-I activity. Taken together, our findings indicate that CWP232228 offers a candidate therapeutic agent for breast cancer that preferentially targets BCSC as well as bulk tumor cells.

Definition of smad3 phosphorylation events that affect malignant and metastatic behaviors in breast cancer cells.

Smad3, a major intracellular mediator of TGFß signaling, functions as both a positive and negative regulator in carcinogenesis. In response to TGFß, the TGFß receptor phosphorylates serine residues at the Smad3 C-tail. Cancer cells often contain high levels of the MAPK and CDK activities, which can lead to the Smad3 linker region becoming highly phosphorylated. Here, we report, for the first time, that mutation of the Smad3 linker phosphorylation sites markedly inhibited primary tumor growth, but significantly increased lung metastasis of breast cancer cell lines. In contrast, mutation of the Smad3 C-tail phosphorylation sites had the opposite effect. We show that mutation of the Smad3 linker phosphorylation sites greatly intensifies all TGFß-induced responses, including growth arrest, apoptosis, reduction in the size of putative cancer stem cell population, epithelial-mesenchymal transition, and invasive activity. Moreover, all TGFß responses were completely lost on mutation of the Smad3 C-tail phosphorylation sites. Our results demonstrate a critical role of the counterbalance between the Smad3 C-tail and linker phosphorylation in tumorigenesis and metastasis. Our findings have important implications for therapeutic intervention of breast cancer.

PTEN loss-mediated Akt activation increases the properties of cancer stem-like cell populations in prostate cancer.

OBJECTIVE: To demonstrate that the PTEN/PI3K/Akt/NF-κB pathway plays an important role in regulating the prostate cancer stem-like cell population by upregulating ABCG2. METHODS: Targeted PTEN knockdown in human prostate DU145 and 22Rv1 cells using a small interfering RNA were confirmed by immunoblot analysis using antibodies of PTEN, phospho-Akt, Akt, and α-tubulin. Knockdown PTEN DU145 and 22Rv1 cells were augmented, and the stem cell-like properties were examined by cell viability and tumor sphere formation and treated by Akt IV inhibitor to provide the signal transduction pathway. Luciferase activity assays were performed. RESULTS: The knockdown of PTEN in prostate cancer cell lines increased the stem-like properties of the cells, including their sphere-forming ability, stem cell population number, epithelial-mesenchymal transition-related gene expression, and ABCG2 expression. Additionally, PTEN expression was highly associated with elevated expression of phospho-Akt. Treatment with an Akt inhibitor suppressed the PTEN-mediated effects on the properties of these stem-like cells as well as drug resistance, ABCG2 expression, and the NF-κB pathway. CONCLUSION: The loss of PTEN in prostate cancer cells resulted in an increased PI3K/Akt pathway. Due to the Akt activation, PTEN loss may play an important role in prostate cancer by promoting cancer stemness through a mechanism that involves enhanced NF-κB signaling.

High aldehyde dehydrogenase activity enhances stem cell features in breast cancer cells by activating hypoxia-inducible factor-2α.

High aldehyde dehydrogenase (ALDH) activity has been recognized as a marker of cancer stem cells (CSCs) in breast cancer. In this study, we examined whether inhibition of ALDH activity suppresses stem-like cell properties in a 4T1 syngeneic mouse model of breast cancer. We found that ALDH-positive 4T1 cells showed stem cell-like properties in vitro and in vivo. Blockade of ALDH activity reduced the growth of CSCs in breast cancer cell lines. Treatment of mice with the ALDH inhibitor diethylaminobenzaldehyde (DEAB) significantly suppressed 4T1 cell metastasis to the lung. Recent evidence suggests that ALDH affects the response of stem cells to hypoxia; therefore, we examined a possible link between ALDH and hypoxia signaling in breast cancer. Hypoxia-inducible factor-2α (HIF-2α) was highly dysregulated in ALDH-positive 4T1 cells. We observed that ALDH was highly correlated with the HIF-2α expression in breast cancer cell lines and tissues. DEAB treatment of breast cancer cells reduced the expression of HIF-2α in vitro. In addition, reduction of HIF-2α expression suppressed in vitro self-renewal ability and in vivo tumor initiation in ALDH-positive 4T1 cells. Therefore, our findings may provide the evidence necessary for exploring a new strategy in the treatment of breast cancer.

Inhibition of Wnt1 expression reduces the enrichment of cancer stem cells in a mouse model of breast cancer.

Breast cancer is the leading cause of deaths from cancer in women. Cancer recurrence is the most common cause of mortality in breast cancer patients. The cancer stem cell (CSC) hypothesis proposes that CSCs are the center of cancer development and recurrence. Targeting CSCs, in combination with standard chemotherapy, may prevent cancer recurrence and improve long-term survival. Stem cells can be enriched in non-adherent sphere cultures. To identify molecular targets in breast CSCs, we evaluated the transcription levels of stem cell-related genes in 4T1 mouse mammary cancer cells grown as spheres or in a monolayer culture. The most differentially expressed gene was found to be wingless-type MMTV integration site family member 1 (Wnt1) in the 4T1 sphere culture. Functionally, knockdown of Wnt1 in breast cancer cell lines suppressed the in vitro properties of the stem-like cells, including their sphere-forming ability and ALDH activity, whereas the addition of recombinant Wnt1 to breast cancer cell lines enhanced the in vitro properties of these stem-like cells. In addition, knockdown of Wnt1 in 4T1 cells affected the properties of the stem-like cells in vivo, including their tumorigenic potential and tumor initiation ability. Collectively, these results suggest that Wnt1 expression may give rise to the properties of CSCs in breast tumors. Therefore, targeting Wnt1-associated signaling proteins may provide an effective therapeutic approach for the treatment of advanced breast cancer.

Dysadherin expression promotes the motility and survival of human breast cancer cells by AKT activation.

High dysadherin expression has been recognized as a biological predictor of metastasis and poor prognosis for many different cancer types; however, the molecular mechanisms of how dysadherin affects cancer progression are still poorly understood. In this study, we examined whether AKT signaling could link dysadherin expression with downstream events that promote the metastatic potential of human breast cancer cells. Immunohistochemical analysis of breast cancer tissues showed that dysadherin expression was highly associated with elevated expression of phospho-AKT. The introduction of dysadherin cDNA into BT-474, MCF-7 and T-47D breast cancer cell lines enhanced their levels of AKT phosphorylation, while knockdown of dysadherin in MDA-MB-231 and Hs578T breast cancer cell lines suppressed AKT phosphorylation. Treatment with the AKT inhibitor triciribine suppressed dysadherin-mediated pro-metastatic effects, including epithelial-mesenchymal transition, cell motility and drug resistance. These findings suggest that dysadherin might contribute to breast cancer progression through AKT activation.

OCT4 Expression Enhances Features of Cancer Stem Cells in a Mouse Model of Breast Cancer.

The cancer stem cell (CSC) hypothesis proposes that CSCs are responsible for metastasis and disease recurrence. Therefore, targeting CSCs has the potential to significantly improve outcomes for cancer patients. The OCT4 transcription factor gene is a master gene that plays a key role in the self-renewal and pluripotency of stem cells. In this study, we introduced an OCT4 reporting vector into 4T1 mouse breast cancer cells and sorted OCT4 high and OCT4 low cell populations. We then determined whether OCT4 expression is associated with maintenance and expansion of CSCs. We found that OCT4(high) 4T1 cells have an increased ability to form tumorsphere and a high expression of stem cell markers such as Sca-1, CD133, CD34, and ALDH1, when compared with OCT4(low) 4T1 cells. In addition, OCT4(high) 4T1 cells have greater tumorigenic potential in vivo. These findings suggest that OCT4 expression may be a useful target for stem cell-specific cancer therapy.

Dysadherin can enhance tumorigenesis by conferring properties of stem-like cells to hepatocellular carcinoma cells.

BACKGROUND & AIMS: Hepatocellular carcinoma (HCC) is associated with a high potential for metastasis and disease recurrence, even after surgical resection. The cancer stem cell (CSC) hypothesis proposes that CSCs are responsible for chemo-resistance, recurrence, and metastasis. Dysadherin is a prognostic indicator of metastasis and poor survival in many different cancer types. In this study, we investigated the possible link between dysadherin and CSC in HCC. METHODS: We analyzed the functional implications of dysadherin on cancer stemness by modification of the dysadherin gene in HCC cell lines. RESULTS: The transfection of dysadherin cDNA into the liver cancer cell line PLC/PRF/5 enhanced the properties of CSCs, including anti-apoptosis, their sphere-forming ability, side population phenotype, and tumor initiation ability in vivo. Furthermore, knockdown of dysadherin in the liver cancer cell line SK-Hep1 suppressed its stem cell-like properties. CONCLUSIONS: These results show that dysadherin give rise to properties of CSC in HCC. Therefore, these findings suggest that dysadherin may be a potential molecular prognostic marker of HCC and may aid in the development of more effective therapies.

Inhibitor of DNA-binding 4 contributes to the maintenance and expansion of cancer stem cells in 4T1 mouse mammary cancer cell line.

The cancer stem cell (CSC) hypothesis proposes that CSCs are the root of cancer. CSC-targeted therapies may prevent cancer relapse and provide more effective treatment. The expression of aldehyde dehydrogenase 1, as assessed by the Aldefluor assay, has been recognized as a marker of CSCs in breast cancer. Inhibitors of DNA-binding proteins (IDs) have an important role in stem cell differentiation. In this study, we examined IDs necessary for the regulation of stem properties in Aldefluor(pos) 4T1 cells. When the expression profile of IDs in Aldefluor(neg) and Aldefluor(pos) 4T1 cells was compared, qRT-PCR analysis showed that ID4 expression was highly upregulated in Aldefluor(pos) 4T1 cells. In addition, knockdown of ID4 expression suppressed the properties of CSCs, including their sphere-forming ability and side population phenotype. The findings suggest that ID4 may be a therapeutic target for the treatment of advanced breast cancer.

Ras activation contributes to the maintenance and expansion of Sca-1pos cells in a mouse model of breast cancer.

The cancer stem cell (CSC) hypothesis proposes that CSCs are the root of cancer and cause cancer metastasis and recurrence. In this study, we examined whether Ras signaling is associated with stemness of the CSCs population characterized by the stem cell antigen (Sca-1) phenotype in a 4T1 syngeneic mouse model of breast cancer. The Sca-1(pos) putative CSCs had high levels of activated Ras and phosphorylated MEK (p-MEK), compared with counterparts. The Ras farnesylation inhibitor (FTI-277) suppressed the maintenance and expansion of CSCs. Therefore, selective inhibition of Ras activation may be useful for stem-specific cancer therapy.

IL-4-induced AID expression and its relevance to IgA class switch recombination.

Activation-induced cytidine deaminase (AID) is an inducible gene that plays a critical role in Ig class switch recombination and somatic hypermutation in B cells. We explored the mechanisms by which IL-4 induces AID expression in mouse B cells. IL-4 increased AID expression and over-expression of Stat6 further augmented IL-4-induced promoter activity. The involvement of Stat6 in the promoter activity was confirmed using ChIP assays and site-directed mutagenesis. Treatment with H89, a PKA inhibitor, markedly decreased IL-4-induced AID expression, and over-expression of CREB enhanced it. These results indicate that Stat6 and PKA/CREB are involved in IL-4-induced AID expression. The relevance of these signal transducing molecules was verified using the TGFbeta1-induced IgA isotype switching model. Our results indicate that IL-4, through Stat6 and PKA/CREB, induces AID expression leading to Ig isotype switching event.