Paula D. Bos

Genes that mediate breast cancer metastasis to lung

By means of in vivo selection, transcriptomic analysis, functional verification and clinical validation, here we identify a set of genes that marks and mediates breast cancer metastasis to the lungs. Some of these genes serve dual functions, providing growth advantages both in the primary tumour and in the lung microenvironment. Others contribute to aggressive growth selectively in the lung. Many encode extracellular proteins and are of previously unknown relevance to cancer metastasis.

Metastasis: from dissemination to organ-specific colonization

Metastasis to distant organs is an ominous feature of most malignant tumours but the natural history of this process varies in different cancers. The cellular origin, intrinsic properties of the tumour, tissue affinities and circulation patterns determine not only the sites of tumour spread, but also the temporal course and severity of metastasis to vital organs. Striking disparities in the natural progression of different cancers raise important questions about the evolution of metastatic traits, the genetic determinants of these properties and the mechanisms that lead to the selection of metastatic cells.

Endogenous human microRNAs that suppress breast cancer metastasis

A search for general regulators of cancer metastasis has yielded a set of microRNAs for which expression is specifically lost as human breast cancer cells develop metastatic potential. Here we show that restoring the expression of these microRNAs in malignant cells suppresses lung and bone metastasis by human cancer cells in vivo. Of these microRNAs, miR-126 restoration reduces overall tumour growth and proliferation, whereas miR-335 inhibits metastatic cell invasion. miR-335 regulates a set of genes whose collective expression in a large cohort of human tumours is associated with risk of distal metastasis. miR-335 suppresses metastasis and migration through targeting of the progenitor cell transcription factor SOX4 and extracellular matrix component tenascin C. Expression of miR-126 and miR-335 is lost in the majority of primary breast tumours from patients who relapse, and the loss of expression of either microRNA is associated with poor distal metastasis-free survival. miR-335 and miR-126 are thus identified as metastasis suppressor microRNAs in human breast cancer.

Genes that mediate breast cancer metastasis to the brain

The molecular basis for breast cancer metastasis to the brain is largely unknown. Brain relapse typically occurs years after the removal of a breast tumour, suggesting that disseminated cancer cells must acquire specialized functions to take over this organ. Here we show that breast cancer metastasis to the brain involves mediators of extravasation through non-fenestrated capillaries, complemented by specific enhancers of blood–brain barrier crossing and brain colonization. We isolated cells that preferentially infiltrate the brain from patients with advanced disease. Gene expression analysis of these cells and of clinical samples, coupled with functional analysis, identified the cyclooxygenase COX2 (also known as PTGS2), the epidermal growth factor receptor (EGFR) ligand HBEGF, and the α2,6-sialyltransferase ST6GALNAC5 as mediators of cancer cell passage through the blood–brain barrier. EGFR ligands and COX2 were previously linked to breast cancer infiltration of the lungs, but not the bones or liver, suggesting a sharing of these mediators in cerebral and pulmonary metastases. In contrast, ST6GALNAC5 specifically mediates brain metastasis. Normally restricted to the brain, the expression of ST6GALNAC5 in breast cancer cells enhances their adhesion to brain endothelial cells and their passage through the blood–brain barrier. This co-option of a brain sialyltransferase highlights the role of cell-surface glycosylation in organ-specific metastatic interactions.

Mediators of vascular remodelling co-opted for sequential steps in lung metastasis

Metastasis entails numerous biological functions that collectively enable cancerous cells from a primary site to disseminate and overtake distant organs. Using genetic and pharmacological approaches, we show that the epidermal growth factor receptor ligand epiregulin, the cyclooxygenase COX2, and the matrix metalloproteinases 1 and 2, when expressed in human breast cancer cells, collectively facilitate the assembly of new tumour blood vessels, the release of tumour cells into the circulation, and the breaching of lung capillaries by circulating tumour cells to seed pulmonary metastasis. These findings reveal how aggressive primary tumorigenic functions can be mechanistically coupled to greater lung metastatic potential, and how such biological activities may be therapeutically targeted with specific drug combinations.

Lung metastasis genes couple breast tumor size and metastatic spread

The association between large tumor size and metastatic risk in a majority of clinical cancers has led to questions as to whether these observations are causally related or whether one is simply a marker for the other. This is partly due to an uncertainty about how metastasis-promoting gene expression changes can arise in primary tumors. We investigated this question through the analysis of a previously defined “lung metastasis gene-expression signature” (LMS) that mediates experimental breast cancer metastasis selectively to the lung and is expressed by primary human breast cancer with a high risk for developing lung metastasis. Experimentally, we demonstrate that the LMS promotes primary tumor growth that enriches for LMS+ cells, and it allows for intravasation after reaching a critical tumor size. Clinically, this corresponds to LMS+ tumors being larger at diagnosis compared with LMS− tumors and to a marked rise in the incidence of metastasis after LMS+ tumors reach 2 cm. Patients with LMS-expressing primary tumors selectively fail in the lung compared with the bone or other visceral sites and have a worse overall survival. The mechanistic linkage between metastasis gene expression, accelerated tumor growth, and likelihood of metastatic recurrence provided by the LMS may help to explain observations of prognostic gene signatures in primary cancer and how tumor growth can both lead to metastasis and be a marker for cells destined to metastasize.

Transient regulatory T cell ablation deters oncogene-driven breast cancer and enhances radiotherapy.

Transient ablation of regulatory T cells in a murine model of breast carcinogenesis inhibits primary tumor and lung metastatic growth and enhances the therapeutic effect of radiotherapy, but not immune checkpoint blockade.

IL-2–dependent adaptive control of NK cell homeostasis

T reg cells restrain IL-2–mediated expansion of immature CD127+ NK cells.

Modeling metastasis in the mouse

Metastasis is a complex clinical and biological problem presently under intense study, and several model systems are in use to experimentally recapitulate and dissect the various steps of the metastatic process. Genetically engineered mouse models provide faithful renditions of events in tumor progression, angiogenesis, and local invasion that set the stage for metastasis, whereas engrafting of human or mouse tumor tissues into mouse hosts has been successfully exploited to investigate metastatic dissemination and colonization of distant organs. Real-time, high-resolution microscopy in live animals, and comprehensive genetic and molecular profiling are effective tools to interrogate diverse metastatic cancer cell phenotypes as well as the metastatic tumor microenvironment in different organs. By integrating the information obtained with these complementary approaches the field is currently obtaining an unprecedented level of understanding of the biology, molecular basis, and therapeutic vulnerabilities of metastasis.

Treg Cells in Cancer: A Case of Multiple Personality Disorder

Foxp3+ RORγt–expressing T cells expand in colorectal cancer and contribute to pathogenesis in a mouse model of polyposis. Foxp3+ RORγt–expressing T cells expand in colorectal cancer and contribute to pathogenesis in a mouse model of polyposis.