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    Research Grants Awarded

    Identification And Targeting Of Adipose Stem Cell Markers For Breast Cancer Therapy

    Grant Mechanism:
    Postdoctoral Fellowships

    Scientific Abstract:
    Obesity, marked by outgrowth of white adipose tissue (WAT), is associated with increased breast cancer progression. The mechanism of obesity effect on the morbidity and mortality of cancer is uncertain. WAT has been recognized as a source of adult stem cells of mesenchymal origin, termed adipose stem (stromal) cells (ASC). Circulating vascular precursor cells, similar or identical to ASC, have been recently shown to be capable of homing to tumors and promoting the formation of cancer vasculature, which is required for expansion of tumor mass. We propose that WAT has a direct positive effect on tumor growth as a source of ASC that are recruited by tumors to participate in blood vessel formation as vascular progenitor cells. Our objective is to use clinical patient samples to test the role of ASC in obesity-cancer interaction. We will also use mouse models to determine the effect of WAT content reduction on ASC circulation and breast cancer progression, which will test our hypothesis. As a result of this study, the role of ASC in breast cancer progression will be tested, our understanding of obesity as a cancer risk factor will be advanced, and a novel approaches to breast cancer management will be explored. We will identify and characterize new ASC ligand/receptor systems to build the platform for ASC targeting with the ultimate goal of preventing ASC-mediated induction of cancer progression. These new ASC markers may become universally useful for imaging and prospective isolation of patient stem cells. The mechanism of WAT influence on cancer progression has not been systematically explored. Here, we propose to investigate the role of ASC in breast tumor growth and to design an approach to ASC targeting. Specifically, we will: (1) Explore whether ASC are mobilized from WAT by obesity and breast cancer; (2) Test whether breast caner progression can be modulated through WAT depletion; and (3) Develop an approach to ablate ASC in vivo through peptides targeting ASC markers. For Specific Aim (1), by using patient blood samples, we will explore whether the frequency of ASC in the systemic circulation is elevated by obesity and breast cancer. Multi-parametric flow cytometry on peripheral blood mononuclear cells, combined with culture colony-formation and differentiation assays, will be used. For Specific Aim (2), ?molecular liposuction? with a WAT vasculature-targeted proapoptotic peptide developed by our group (Nat. Med. 2004,10:625-32) will be used to test the effect of WAT on cancer progression. By inducing obesity with high-fat diet in several breast cancer models (MMTV-TGF-alpha transgenic mice, murine EF43.fgf4 mammary breast carcinoma allografts, and human MDA-231breast carcinoma xenografts), we will establish tumors in the obesity background and then perform the experimental WAT depletion. Tumor analysis will be then performed to assess whether obesity reversal via reduction of the amount of WAT inhibits or promotes tumor growth in animals carrying breast carcinoma. In parallel, to determine whether ASC escape the WAT cytoablation treatment and become avalible for tumor vasculogenesis, we will quantify ASC content in blood of mice treated with the proapoptotic peptide. Finally, to isolate ASC-targeting peptides in Specific Aim (3), we will employ our exclusive expertise in selecting combinatorial peptide libraries displayed on bacteriophage to identify molecular interactions that occur at the ASC surface in vivo. As a logical evolution of this study, we are planning to eventually explore ASC as a potential therapeutic target. We will direct the pro-apoptotic peptide with an ASC-targeting ligand to ablate ASC in mouse breast cancer models. The experimental strategy proposed here to deplete WAT and explore the response in the course of breast cancer progression will make it possible to uncouple the presence of WAT in the body from the obesity-inducing factors (diet). This study will, for the first time, directly assign the role of WAT in breast cancer. Furthermore, we will look into possible new biological bases of breast cancer progression by testing the role of ASC in the WAT-tumor crosstalk. Because the possible mobilization of ASC in obesity so far has not been tested or even proposed, this will be the original, highly cited, study measuring ASC in circulation. If observed, inhibition of tumor growth by targeted ASC depletion will strongly support our theory that ASC, rather than adipokines, play the key role in cancer progression. Establishing the role of physiological stem cells in malignant disease could eventually be translated into approaches to surveillance of these cells in circulation for cancer prognosis and their targeting for cancer therapy. Finding out whether ASC are the key component of WAT that is activated upon obesity treatment and engages in tumor vasculogenesis is of detrimental importance. Proving or disproving ASC as a functional link between cancer and obesity, and/or as a potential therapeutic target, is essential for strategizing obesity management. If our hypothesis that WAT-derived adult stem cells directly promote tumor growth in vivo is confirmed, the understanding of cancer risk factors and approaches to breast cancer therapy in obese patients will have to be re-evaluated. It is possible that obesity therapy in breast cancer patients may accelerate tumor growth through ASC mobilization, however, introducing a combination ASC inactivation, prototyped by our work, may overcome this complication. In the future, anti-ASC therapy could become a cancer treatment complementary to drugs directed at tumors.

    Lay Abstract:
    Obesity, manifested by overgrowth of white fat (adipose) tissue, a widespread problem among middle-aged women, has been associated with advanced progression of breast cancer. The mechanism of obesity influence on cancer is not understood. It has been proposed that adipose tissue directly promotes cancer. The study hypothesis: According to our theory, adipose tissue may influence cancer progression through its effect on formation of new blood vessels, the process necessary for expansion of tumor mass. While the involvement of circulating vascular progenitors in tumor vasculogenesis, and their cancer-stimulatory effect, has been demonstrated, the origin of these cells has remained controversial. Here, we propose a novel hypothesis, according to which tumor vasculogenesis relies on adult adipose stem cells (ASC), an abundant population of white fat stromal cells. Because tumors secrete various chemokines (molecules attracting stem cells), it is possible that ASC of obese patients become mobilized and are recruited as a source of vascular precursors for tumor blood vessels. To explore the role of adipose-derived stem cells in promoting breast cancer, we will use patient blood samples and mouse tumor models for several critical experiments that will investigate whether ASC are shed into circulation by pathologically overgrown fat tissue and hijacked by tumors to promote vasculogenesis. By quantifying stem cell content in systemic circulation, we will explore whether ASC are mobilized from fat tissue of patients in response to pathological obesity and breast tumor growth. An experimental approach to reduce body fat content developed by our group (Nature Medicine 2004, 10:625-32) will provide a unique opportunity to assess the influence of adipose tissue on cancer independently from environmental factors. We will test whether such ?molecular liposuction? can change the course of breast caner progression in the mouse model. The tumor response to white fat mass reduction will be correlated with the changes in adipose stem cell circulation. In case if viable ASC are found to be mobilized by obesity reversal and associate with enhanced growth of tumors, our hypothesis will be confirmed. As the final aim of our study, we propose to develop approaches to ablating ASC through peptides targeting their differentially expressed cell surface receptors. Advancing understanding of breast cancer / importance of the research to patients: As a result of this study, the importance of white fat-associated factors for breast cancer progression will be realized. Whether our hypothesis is confirmed or not, as a result of this project, ASC will be better understood as a factor implicated in the pathology of obesity and cancer. In addition, our work will advance the field of basic stem cell biology. There are currently no markers available that would distinguish ASC from adult mesenchymal cells residing in other organs. Identification of ASC markers proposed here will lead to better understanding of the relationship between different types of adult stem cells and of chemotactic gradients controlling their mobilization and tumor homing. Our studies will shift the paradigms in the biology of obesity and cancer, thus setting new directions for subsequent clinical research, and may establish a basis for the development of new approaches to targeting stem cells for therapeutic purposes. Assigning the role for the ASC, or absence of such, in breast cancer progression is critical for strategizing cancer treatment, as it might be realized that obesity therapy in patients could be harmful, rather than beneficial, without a combination measure to inactivate the released ASC. In the future, depletion of adipose vascular progenitor cell pool could become an approach to cancer treatment and possibly a measure for the suppression of breast cancer progression. In addition, our study will help to address the safety of adult stem cells currently being investigated in various pre-clinical trials for potential therapeutic applications in breast cancer patients.