Dynamic Tumor Microenvironment Research Articles

Abstract B27: Osteoprotegerin's key role in inflammatory breast cancer: Bane or Boon.

Abstract Inflammatory breast cancer (IBC), the most aggressive form of breast cancer is presented with a rapidly enlarging erythematous breast, often with no discernible breast mass. IBC is lethal, highly metastatic and accounts for less than 5% of all diagnosed breast cancers; although in young African-American women recurrence rates are as high as 50%. Despite multimodality treatments such as systemic chemotherapy, adjuvant therapy, surgery and radiation, there is dismal prognosis with a 3-year survival rate of only about 40% compared to 85% among patients with non-IBC. Our long-term goal is to understand IBC biology, to evaluate its unique tumor microenvironment (TME), and to use that information to improve diagnosis, management, and survival rate in IBC patients. A proactive, complex and dynamic TME adds to the grim scenario of the disease by accumulating inflammatory and angiogenic growth factors and creating a niche for tumor cells. These cells rely on their TME which can drive a latent tumor to grow into different from the gross metastasis. Here, we performed thorough analysis and comparison of cytokine levels in the conditioned media obtained from inflammatory breast cancer (SUM149PT, SUM1315MO2; cells obtained from primary inflammatory ductal carcinoma of the breast) and normal cell lines (Primary human mammary epithelial cells; HMEC, 184B5; cells of normal mammary tissue obtained from a normal reduction mammoplasty). Inflammatory breast cancer cell lines secrete higher levels of cytokines such as osteoprotegerin (OPG), GRO, GRO-α, MIF, and MIP-1α. To fully comprehend the role of inflammatory cytokines in breast cancer tumorigenesis, we used “mammospheres” also known as tumorspheres or multicellular spheroids. Mammospheres represents an in vitro cultivation system which allows undifferentiated human mammary epithelial cells in suspension to propagate and form non-adherent colonies which recapitulate the in vivo spatial orientation. We compared the composition of conditioned media obtained from inflammatory breast cancer cell line and primary human mammary epithelial cell mammospheres. We observed striking differences in the level of osteoprotegerin (OPG) in the inflammatory breast cancer mammosphere conditioned medium as compared the one obtained from primary human mammary epithelial cells. We focused our study on OPG, a secreted member of the TNF superfamily that acts as a decoy receptor for the receptor activator of nuclear factor kappa B ligand (RANKL). Our work highlights the potential involvement of OPG in IBC tumor cell survival, metastases and reprogramming of mammosphere characteristics (size, number and, proliferation index) thus adding to the severity of disease. Collectively, our study significantly contributes to the understanding the role of OPG in cellular and molecular events involved in IBC progression and opens new avenues for strategic targeting of OPG and the development of novel therapeutic modalities for IBC. Citation Format: Sudeshna Goswami, Neelam Sharma-Walia. Osteoprotegerin's key role in inflammatory breast cancer: Bane or boon. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B27.

Tumor Hypoxia as a Modifier of DNA Strand Break and Cross-Link Repair

Hypoxia is a common characteristic of many solid tumors and is associated with poor prognosis. Cells with low oxygen levels can have altered sensitivity to radiotherapy and chemotherapy secondary to changes in the incidence of DNA single- and double-strand breaks (DNA-ssb, DNA-dsb), DNA base damage, DNA-DNA cross-links and DNA-protein cross-links. Recent evidence also supports that cells exposed to chronic hypoxia have a decreased capacity of DNA-dsb repair. This review will examine the influence of short-term and prolonged hypoxia on the two major pathways of DNA-dsb repair: homologous recombination (HR) and non-homologous end-joining (NHEJ). Novel treatment strategies designed to exploit the hypoxic tumor microenvironment are also discussed. Modification of DNA damage sensing and repair due to fluctuating oxygen levels within a dynamic tumor microenvironment may have profound implications for tumor progression and treatment.

Spontaneous immune responses to sporadic tumors: tumor-promoting, tumor-protective or both?

Cancer cells cannot develop into invasive cancers without interactions with cells and soluble mediators present in the tumor microenvironment. Accumulating evidence indicates that the immune system is a critical determinant of malignant outgrowth; however, the tumor-modulating effects of spontaneous immune responses towards nascent malignancies are rather paradoxical. Both cancer-protective and cancer-promoting features of the immune system have been described. This review will discuss the role of the dynamic inflammatory tumor microenvironment during cancer development and progression, and will focus on the intriguing question: "Do malignancies develop in spite of-or because of-spontaneous immune responses?" Special emphasis will be put on recent progress in our understanding of the immune system's double-edged sword function during de novo carcinogenesis.

Phosphorylation of eIF2α is required for mRNA translation inhibition and survival during moderate hypoxia

Human tumors are characterized by temporal fluctuations in oxygen tension. The biological pathways that respond to the dynamic tumor microenvironment represent potential molecular targets for cancer therapy. Anoxic conditions result in eIF2alpha dependent inhibition of overall mRNA translation, differential gene expression, hypoxia tolerance and tumor growth. The signaling pathway which governs eIF2alpha phosphorylation has therefore emerged as a potential molecular target. In this study, we investigated the role of eIF2alpha in regulating mRNA translation and hypoxia tolerance during moderate hypoxia. Since other molecular pathways that regulate protein synthesis are frequently mutated in cancer, we also assessed mRNA translation in a panel of cell lines from different origins. Immortalized human fibroblast, transformed mouse embryo fibroblasts (MEFs) and cells from six cancer cell lines were exposed to 0.2% or 0.0% oxygen. We assayed global mRNA translation efficiency by polysome analysis, as well as proliferation and clonogenic survival. The role of eIF2alpha was assessed in MEFs harboring a homozygous inactivating mutation (S51A) as well as in U373-MG cells overexpressing GADD34 (C-term) under a tetracycline-dependent promoter. The involvement of eIF4E regulation was investigated in HeLa cells stably expressing a short hairpin RNA (shRNA) targeting 4E-BP1. All cells investigated inhibited mRNA translation severely in response to anoxia and modestly in response to hypoxia. Two independent genetic cell models demonstrated that inhibition of mRNA translation in response to moderate hypoxia was dependent on eIF2alpha phosphorylation. Disruption of eIF2alpha phosphorylation caused sensitivity to hypoxia and anoxia. Disruption of eIF2alpha phosphorylation is a potential target for hypoxia-directed molecular cancer therapy.