Available online http://breast-cancer-research.com/contents/7/3/113 Meeting report Keystone symposium: The role of microenvironment in tumor induction and progression, Banff, Canada, 5–10 February 2005 Jamie L Bascom and Paraic A Kenny Life Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, USA Corresponding author: Paraic A. Kenny, [email protected] Published: 6 April 2005 Breast Cancer Research 2005, 7:113-118 (DOI 10.1186/bcr1030) This article is online at http://breast-cancer-research.com/content/7/3/113 © 2005 BioMed Central Ltd Abstract detailing crucial interactions between epithelial and stromal The first Keystone symposium on the role of microenvironment in cells during both normal mammary development and tumor induction and progression attracted 274 delegates from 13 tumorigenesis. She described a series of wild-type/knockout countries to Banff in the heart of the Canadian Rockies. The tissue recombination experiments used to dissect the meeting was organized by Mina Bissell, Ronald DePinho and Luis requirements for epithelially and stromally expressed growth Parada, and was held concurrently with the Keystone symposium factors and receptors in mammary gland development. In a on cancer and development, chaired by Matthew Scott and lecture that was both visually and intellectually stimulating, Roeland Nusse. The 30 oral presentations and over 130 posters provided an excellent forum for discussing emerging data in this she showed that intravital imaging technology is a valuable rapidly advancing field. tool with which to interrogate the interactions between stromal and epithelial cells in tumorigenesis. Time-lapse fluorescent videos using mouse mammary tumor virus-polyoma Introduction middle T antigen (MMTV-PyMT) transgenic mice bearing It is now apparent that reciprocal interactions between tumor various fluorescent markers demonstrated the dynamic inter- cells and their microenvironment — extracellular matrix (ECM), actions between the tumor and host cellular components. growth factors, fibroblasts, immune and endothelial cells — play an essential role in the earliest stages of transformation In the second keynote address, Joan Massagué (Memorial to malignant progression and metastasis. By better Sloan Kettering Cancer Center, New York), described a understanding the complex interactions between all of these series of experiments that probed the nature of pre-metastatic factors, it is hoped that therapies might be effectively cells. Cells from primary tumors in specific organs tend to targeted against both epithelial and stromal determinants of have a tropism for successful metastasis to distant sites (e.g. tumor progression. In this regard, there were several breast cancer to bone, lung, liver, and brain; and colon encouraging presentations on novel clinical approaches that cancer to liver). To what extent are these preferences pre- target these processes. specified in the primary tumor cell population? To address this question, Massagué used a metastatic breast cancer cell Skiers and snowboarders among the delegates were blessed line, MDA-MB-231, and used nude mice as a ‘cell sorter’ by with 67 cm of fresh snow just prior to arrival, resulting in a introducing cells and collecting and testing those that stampede for the ski buses each day at 11 am. The quality of established metastatic colonies in particular organs. He the meeting was perhaps best reflected by an equally urgent showed that this cell line is indeed composed of stampede back to the conference center in time for the subpopulations with distinct metastatic characteristics that evening sessions and posters. correlate with particular transcriptional profiles [1]. He has begun to analyze the functional relevance of these Zena Werb (University of California, San Francisco) set the correlations in overexpression and small interfering RNA scene for the meeting with a wide ranging plenary lecture (siRNA) studies. CSF1 = colony stimulating factor 1; ECM = extracellular matrix; ES = embryonic stem; HGF = hepatocyte growth factor; HIF-1α = hypoxia inducible factor 1α; MMP = matrix metalloproteinase; MMTV = mouse mammary tumor virus; MSF1 = migration stimulating factor 1; PyMT = polyoma middle T antigen; SF/HGF = scatter factor/hepatocyte growth factor; siRNA = small interfering RNA; TGCT = testicular germ cell tumor; TGFβ = transforming growth factor β; TGFβR2 = transforming growth factor β receptor 2; TNC = tenascin C; TSP-1 = thrombospondin-1; VEGF = vascular endothelial growth factor. 113 Breast Cancer Research May 2005 Vol 7 No 3 Bascom and Kenny Angiogenesis and microenvironment organize to form ECM-rich fluid conducting ductal networks The Monday morning session focused on the role of the within the tumor, lined by the tumor cells themselves and microenvironment during angiogenesis. The speakers connected to the vasculature of the host. This reorganization described the regulation of angiogenesis, both by of the tumor cells facilitates the supply of oxygen and transcriptional programs and by extracellular pro- and anti- nutrients. Hendrix also showed that these networks are angiogenic factors, and the mechanisms by which tumor resistant to classical inhibitors of angiogenesis, such as angiogenesis might be effectively targeted. endostatin [6]. The first speaker, Luisa Iruela-Arispe (University of California, Microenvironmental influences on metastasis Los Angeles), presented work from her group showing that Interactions between tumor cells and cellular or transgenic overexpression of thrombospondin-1 (TSP-1), an proteinaceous components of their microenvironment may ECM component with anti-angiogenic activity, inhibits angio- inhibit or facilitate metastasis. In this evening session, the genesis and tumor growth in MMTV-Neu mice, and effects a speakers discussed some of the signaling events involved downregulation of matrix metalloproteinase (MMP)-9 and and the identification of pro-metastatic transcriptional decreased expression of vascular endothelial growth factor programs. (VEGF) [2]. Dr Iruela-Arispe’s lab is now working to delineate the different functions of a series of different metallo- Large numbers of tumor-infiltrating macrophages often proteinase cleavage fragments of VEGF in tumor angiogenesis. correlate with poor prognosis. Jeffrey Pollard (Albert Einstein College of Medicine, New York) described his laboratory’s Nancy Boudreau (University of California, San Francisco) work on colony stimulating factor 1 (CSF1), a protein discussed two homeobox transcription factors, HoxD3 and secreted by tumor cells that acts as a potent chemoattractant HoxD10, and their apparently opposing roles in breast cancer for macrophages. Knockout of CSF1 attenuated macrophage (Carrio et al., manuscript submitted). HoxD3, which is not recruitment in the MMTV-PyMT mammary tumor model, expressed in the normal mammary gland, is upregulated resulting in a delayed progression to metastasis of these during breast cancer progression and upregulates several tumors. Conversely, tumor progression and metastasis were ECM remodeling enzymes and angiogenic factors, including accelerated by CSF1 overexpression in the same model. VEGF [3]. In contrast, Hox D10, a potent inhibitor of Thus, CSF1 is implicated in recruiting these VEGF, MMP, angiogenesis, is highly expressed in the normal gland and is and protease secreting pro-angiogenic immune cells to the absent in invasive carcinomas [4]. Currently, Boudreau and tumor, which facilitates tumor progression [7]. colleagues are concentrating on the organizational role that Hox D10 plays in the normal mammary gland using three- Kenneth Pienta (University of Michigan, Ann Arbor) presented dimensional culture assays. gene and protein expression data from primary and metastatic prostate cancers from a series of 32 rapid ‘warm’ Rapidly growing tumors are frequently hypoxic, and autopsies. While bone represented the most common site of neoangiogenesis may be stimulated by hypoxia-dependent metastasis, non-osseous sites included lymph nodes, liver, transcriptional activation. Randall Johnson (University of lung, and adrenal gland. Metastases to different sites (from California, San Diego) described the effect of tissue-specific the same primary tumor) frequently showed significant ablation of hypoxia inducible factor 1α (HIF-1α) in endothelial differences in histology and gene expression [8]. Thus a cells. Loss of HIF-1α blocked neoangiogenesis in in vivo single regimen might not reasonably be expected to treat matrigel plug assays and also resulted in impaired wound such a heterogeneous disease. Pienta outlined an aggressive healing in these mice. Most strikingly, tumor xenografts in multi-targeted chemotherapy approach that he is testing in these mice were smaller and more necrotic than in controls, this patient population. resulting from a greatly reduced microvessel density [5]. Using an approach similar to that outlined by Joan Massagué, A short talk given by Gavin Thurston (Regeneron Richard Hynes (Massachusetts Institute of Technology, Pharmaceuticals, Tarrytown, NY) provided a summary of the Cambridge) isolated lung metastases formed following tail array of drugs in development to target VEGF signaling. He is vein injection of melanoma cell lines [9]. Successive isolation currently studying the efficacy of a decoy receptor for VEGF, and re-injection selected for a highly lung-tropic population. ‘VEGF-TRAP’, against angiogenesis in vivo and has shown Gene expression analysis