Abstract 3866: Inactivation of p53/PTEN confers a specific epigenetic profile regulated by IL6-SOCS3 signaling

Recent studies by us and others suggested that activation of inflammatory feedback loop play critical role in metastasis and therapeutic resistance by regulating EMT/CSC phenotype. Of these cytokines, IL6 is a key regulator of inflammatory responses and orchestrates these physiological functions by controlling the Stat3/NF-kB pathway which is negatively regulated by the suppressor of cytokine signaling 3 (SOCS3). Consistent with these reports, we demonstrated in our preliminary data that SOCS3 is abundantly expressed in non-malignant MCF10A cells as well as in luminal and HER2+ tumors where it negatively regulates the IL6/Stat3/NF-kB signaling. In contrast, SOCS3 protein was undetectable in basal cluadin-low breast cancer cell lines and primary tumors which express substantially higher levels of IL6. We developed transformed MCF10A model by simultaneous knockdown of p53 and PTEN. In this model single p53 and PTEN deletions result in hyperplasia or DCIS-like lesions. Interestingly, SOCS3 protein expression was undetectable in MCF10A-p53-PTEN- cells compared to parental MCF10A, single p53 (MCF10A-p53-) or PTEN (MCF10A-PTEN-) deleted cells. We demonstrated that IL6 mediated Stat3/NF-kB signaling is negatively regulated by SOCS3 that strongly inhibited the IL6/Stat3/NF-kB pathway when overexpressed in MCF10A-p53-PTEN- cells. Moreover, enforced SOCS3 expression in these cells reduced the tumor growth and inhibited metastasis. Furthermore, loss of SOCS3 expression is strongly associated with increased risk of recurrent disease in breast cancer patients. We hypothesized that loss of SOCS3 in TNBCs results in activation of IL6 feedback loop which drives aggressive metastatic phenotype. Interestingly Stat3/NF-kB signaling drives expression of SOCS3 in response to inflammation and serves as negative feedback loop, although molecular mechanism of SOCS3 expression in cancer has not been investigated. IL6 signaling has been previously reported to be involved in epigenetic regulation. We therefore correlated the gene expression and methylation profile after enforced SOCS3 expression. Our analysis revealed that expression levels of a significant number of genes involved in transcription, migration and metabolism were reverted to those of the parental non transformed cells and their transcription was regulated by methylation. These results suggest that interplay between genetic and epigenetic changes during malignant transformation of mammary epithelial cells may activate multiple signaling cascades and reconstitution of SOCS3 may have therapeutic utility in TNBC.

Citation Format: Maria Ouzounova, Gwangil Kim, April Davis, Ahmed A. Quraishi, Nader Tawakkol, Shalini Kota, Max S. Wicha, Hasan Korkaya. Inactivation of p53/PTEN confers a specific epigenetic profile regulated by IL6-SOCS3 signaling. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3866. doi:10.1158/1538-7445.AM2014-3866

Abstract 3869: SOCS3-mediated regulation of inflammatory cytokines in triple-negative breast cancer

We demonstrated that knock-down of tumor suppressors p53 and PTEN in mammary epithelial MCF10A cells (called MCF10A-p53-PTEN-) results in generation of aggressive tumors. Furthermore MCF10A-p53-PTEN- cells also display an increased EMT phenotype as well as expansion of cancer stem cell (CSC) population. Utilizing Affymetrix gene expression analyses, we confirmed that malignant MCF10Ap53-PTEN- cells displayed a gene expression pattern which closely resembled that of the basal/claudin molecular subtype with the TN. This subtype is previously characterized by the expression of EMT and stem cell genes.

The Inflammatory cytokines IL6 and TGF-β have been found to regulate stem cells and EMT. Consistent with these data, we found that MCF10A-p53-PTEN- cells secreted significantly higher levels of IL6 (>1000 fold) and TGF-β (>200 fold) compared to parental or single gene deleted cells. Furthermore combined deletion of p53 and PTEN compared to single gene knockdown resulted in transformation of MCF10A cells generating aggressive metastatic tumors in NOD/SCID mice.

IL6 is a key regulator of inflammatory responses and orchestrates these physiological functions by controlling the SOCS3 mediated Stat3/NF-κB pathway. Consistent with these reports, we demonstrated that SOCS3 is abundantly expressed in MCF10A cells where it negatively regulates the IL6 feedback loop. Unexpectedly, we found that SOCS3 protein was undetectable in MCF10A-p53-PTEN- cells. Basal/claudin-low breast cancer cell lines that display an activated IL6 feedback loop also had low SOCS3 protein levels. Furthermore, we found a similar discordance between SOCS3 protein and mRNA levels in primary basal/claudin-low breast cancer samples as demonstrated by immunochemistry utilizing a primary breast cancer tissue array. Together these findings suggest that loss of SOCS3 protein expression allows for maintenance of the IL6 mediated inflammatory feedback loop in aggressive/metastatic TN breast cancers. We found that MCF10A-p53-PTEN- cells displayed increased proteasome activity as evidenced by SOCS3 protein accumulation upon proteasome inhibition. Proteolytic degradation of SOCS3 protein in turn is controlled by constitutive activation of the IL6 mediated Stat3/NF-κB pathway.

We demonstrate that enforced expression of SOCS3 or IL6 pathway inhibition interfering with this loop through IL6R blockade repress the CSC population, reducing the tumor growth and metastasis in mouse xenografts. These studies provide a strong rationale for development of IL6 pathway-targeting agents for the treatment of TNBC, an aggressive disease that currently lacks molecularly targeted therapeutics.

Citation Format: Hasan Korkaya, Maria Ouzounova, Gwangil Kim, Ali Quraishi, April Davis, Nader Tawakkol, Sumeyye Korkaya, Max S. Wicha. SOCS3-mediated regulation of inflammatory cytokines in triple-negative breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3869. doi:10.1158/1538-7445.AM2014-3869

SOCS3-mediated regulation of inflammatory cytokines in PTEN and p53 inactivated triple negative breast cancer model

Somatic mutations or deletions of TP53 and PTEN in ductal carcinoma in situ (DCIS) lesions have been implicated in progression to invasive ductal carcinomas. A recent molecular and mutational analysis of breast cancers revealed that inactivation of tumor suppressors, p53 and PTEN are strongly associated with triple negative breast cancer. In addition, these tumor suppressors play important roles in regulating self-renewal in normal and malignant stem cells. To investigate their role in breast carcinogenesis, we knocked down these genes in human mammary cells and in non-transformed MCF10A cells. p53 and PTEN knockdown synergized to activate pro-inflammatory IL6/Stat3/NF-κB signaling. This resulted in generation of highly metastatic EMT-like cancer stem cells (CSCs) resulting in tumors whose gene expression profile mimicked that found in basal/claudin-low molecular subtype within the triple negative breast tumors. Constitutive activation of this loop in transformed cells was dependent on proteolytic degradation of SOCS3 resulting in low levels of this protein in basal/claudin low cell lines and primary tumors. In non-transformed cells, transient activation of the IL6 inflammatory loop induced SOCS3 expression leading to pathway inactivation. In transformed cells, enforced expression of SOCS3 or interfering with IL6 pathway via IL6R blockade inhibited tumor growth and metastasis in mouse xenograft models. Furthermore, circulating tumor cells were significantly reduced in tumor bearing animals when treated with anti-IL6R antibodies. These studies uncover important connections between inflammation and carcinogenesis and suggest that blocking pro-inflammatory cytokines may be utilized as an attractive strategy to target triple negative breast tumors which currently lacks molecularly targeted therapies.

HER2 drives luminal breast cancer stem cells in the absence of HER2 amplification: implications for efficacy of adjuvant trastuzumab

Although current breast cancer treatment guidelines limit the use of HER2-blocking agents to tumors with HER2 gene amplification, recent retrospective analyses suggest that a wider group of patients may benefit from this therapy. Using breast cancer cell lines, mouse xenograft models and matched human primary and metastatic tissues, we show that HER2 is selectively expressed in and regulates self-renewal of the cancer stem cell (CSC) population in estrogen receptor-positive (ER(+)), HER2(-) luminal breast cancers. Although trastuzumab had no effects on the growth of established luminal breast cancer mouse xenografts, administration after tumor inoculation blocked subsequent tumor growth. HER2 expression is increased in luminal tumors grown in mouse bone xenografts, as well as in bone metastases from patients with breast cancer as compared with matched primary tumors. Furthermore, this increase in HER2 protein expression was not due to gene amplification but rather was mediated by receptor activator of NF-κB (RANK)-ligand in the bone microenvironment. These studies suggest that the clinical efficacy of adjuvant trastuzumab may relate to the ability of this agent to target the CSC population in a process that does not require HER2 gene amplification. Furthermore, these studies support a CSC model in which maximal clinical benefit is achieved when CSC targeting agents are administered in the adjuvant setting. Cancer Res; 73(5); 1635-46. ©2012 AACR.

Activation of an IL6 inflammatory loop mediates trastuzumab resistance in HER2+ breast cancer by expanding the cancer stem cell population

Although inactivation of the PTEN gene has been implicated in the development of resistance to the HER2 targeting antibody trastuzumab, the mechanisms mediating this resistance remain elusive. We generated trastuzumab resistant cells by knocking down PTEN expression in HER2 overexpressing breast cancer cell lines and demonstrate that development of trastuzumab resistance in these cells is mediated by activation of an IL6 inflammatory feedback loop leading to expansion of the cancer stem cell (CSC) population. Long term trastuzumab treatment generates highly enriched CSCs which display an EMT phenotype secreting over 100-fold more IL6 than parental cells. An IL6 receptor antibody interrupted this inflammatory feedback loop reducing the cancer stem cell population resulting in decreased tumor growth and metastasis in mouse xenographs. These studies demonstrate that trastuzumab resistance may be mediated by an IL6 inflammatory loop and suggest that blocking this loop may provide alternative strategy to overcome trastuzumab resistance.

Abstract 3470: HER2 drives luminal breast cancer stem cells in the absence of HER2 amplification: Implications for efficacy of adjuvant trastuzumab

Although current breast treatment guidelines limit the use of HER2 blocking agents such as trastuzumab to women whose tumors display HER2 gene amplification, recent retrospective analysis by Paik et al., have suggested that a wider group of patients may benefit from this therapy. Utilizing breast cancer cell lines, mouse xenograft models and primary human tumors and metastatic tissues, we provide a potential molecular explanation for these unanticipated clinical finding by demonstrating that HER2 is selectively expressed in the cancer stem cell (CSC) population in luminal ER+ breast cancers that do not display HER2 amplification. Furthermore, we demonstrate that the effects of trastuzumab on mouse tumor xenografts are highly dependent on the timing of administration. While the effects of trastuzumab on established tumors are limited to those with HER2 amplification, when this HER2 blocker is given immediately after tumor inoculation simulating an adjuvant setting, it significantly inhibits the growth of luminal tumors in the absence of HER2 amplification. In addition, HER2 expression is increased in luminal tumors propagated in mouse tibias as compared to primary tumors grown in mammary fat pads. Utilizing co-culture experiments with human osteocytes, we provide evidence that this regulated expression of HER2 is mediated by RANK ligand present in the bone microenvironment. The clinical relevance of these studies is demonstrated in breast cancer tissues by the co-expression of HER2 and CSC marker ALDH1 in a subset of cells which are selectively found at the invasive tumor front in luminal breast cancers. Recapitulating the mouse xenograft studies, we demonstrate increased expression of HER2 in bone metastasis compared to matched primary tumors in 8 patients with luminal breast cancer. Our results have significant clinical implications since they suggest that the benefits of adjuvant HER2 targeting therapies may extend to patients with luminal breast cancers who are currently classified as HER2-negative. Furthermore, these results support the cancer stem cell hypothesis and emphasize the clinical importance of targeting cancer stem cells in the adjuvant setting.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3470. doi:1538-7445.AM2012-3470

Abstract 3349: Transformation of mammary epithelial cells by inactivation of p53 and PTEN generates cancer stem cells driven by an IL-6/TGF-beta inflammatory loop

The PTEN and p53 tumor suppressor genes, frequently inactivated in human breast cancers have been shown to be regulators of normal and malignant breast stem cell self-renewal. In addition, inactivation of tumor suppressors in preneoplastic lesions are implicated in tumor progression from ductal situ in carcinoma (DCIS) to invasive ductal carcinoma. To determine the relationship between stem cell self-renewal and carcinogenesis, we examined the effects of PTEN and p53 knockdown on normal mammary epithelial cells obtained from reduction mammoplasties, as well as in the non-transformed mammary cell line MCF10A. Simultaneous knockdown of PTEN and p53 in normal mammary epithelial cells generated hyperplastic and DCIS-like lesions when these cells were transplanted into the humanized mammary fat pads of NOD/SCID mice. In MCF10A cells knockdown of PTEN and p53 synergized to expand the stem cell compartment transforming these cells and generating highly metastatic tumors in NOD/SCID mice. Stem cell expansion was driven by activation of an inflammatory loop involving both IL-6 and TGF-b. This inflammatory loop was mediated by both AKT/b-Catenin and Stat3/NF-kB pathways. Conversely collective inhibition of these pathways including TGF-b, IL-6 and Wnt/b-Catenin and Stat3/NF-kB was necessary to revert back this stem cell phenotype. This may suggest that synergistic activity of these pathways may contribute to the expansion and transformation of mammary stem cells. The expanded cancer stem cells were highly metastatic and invasive and displayed properties of EMT. The IL6-R antibody tocilizumab blocked this loop resulting in a reduction of CSCs and thus inhibiting tumor growth in mouse xenografts. These studies suggest that loss of PTEN and p53 transforms mammary epithelial cells by activating an inflammatory loop mediated by IL-6 and TGF-b, generating CSCs with an EMT phenotype. Since CSCs drive tumor growth and metastasis, targeting the self-renewal by interfering with this CSC, inflammatory loop represents a rational strategy for breast cancer prevention and therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3349. doi:1538-7445.AM2012-3349