The niche under siege: novel targets for metastasis therapy

Metastasis is an inefficient process and most cancer cells fail to colonize secondary sites. There are several possible reasons for this. First, the nature of the infiltrating cells is important as a small population of cancer stem cells has been shown to have exclusive metastasis-initiating potential. Secondly, supportive niches are required to promote the outgrowth of disseminated tumour cells. S uch niches are either produced prior to the arrival of cancer cells in the target organ or are induced ad hoc upon cell infiltration. Components of the extracellular matrix (ECM) have been found to play a role in establishing these niches. This has highlighted the importance of the ECM for metastatic progression, and suggests that such components may provide alternative targets for treatment of metastastic disease. © 2012 The Association for the Publication of the Journal of Internal Medicine.

Interactions between cancer stem cells and their niche govern metastatic colonization

Hans-Anton Lehr, Ilaria Malanchi, Albert Santamaria Martinez

Metastatic growth in distant organs is the major cause of cancer mortality. The development of metastasis is a multistage process with several rate-limiting steps. Although dissemination of tumour cells seems to be an early and frequent event, the successful initiation of metastatic growth, a process termed 'metastatic colonization', is inefficient for many cancer types and is accomplished only by a minority of cancer cells that reach distant sites. Prevalent target sites are characteristic of many tumour entities, suggesting that inadequate support by distant tissues contributes to the inefficiency of the metastatic process. Here we show that a small population of cancer stem cells is critical for metastatic colonization, that is, the initial expansion of cancer cells at the secondary site, and that stromal niche signals are crucial to this expansion process. We find that periostin (POSTN), a component of the extracellular matrix, is expressed by fibroblasts in the normal tissue and in the stroma of the primary tumour. Infiltrating tumour cells need to induce stromal POSTN expression in the secondary target organ (in this case lung) to initiate colonization. POSTN is required to allow cancer stem cell maintenance, and blocking its function prevents metastasis. POSTN recruits Wnt ligands and thereby increases Wnt signalling in cancer stem cells. We suggest that the education of stromal cells by infiltrating tumour cells is an important step in metastatic colonization and that preventing de novo niche formation may be a novel strategy for the treatment of metastatic disease.

2012

Intestinal stem cells differentiation and its application in cancer therapy

Maxim Norkin

Colorectal cancer (CRC) is one of the deadliest cancers worldwide. Despite extensive research in the field, new therapies targeting CRC are in urgent need. CRC is a highly heterogeneous disease with high levels of intra- and inter-patient heterogeneity. Cancer stem cells are the driving force of tumor development and metastasis. One of the approaches to treat CRC is differentiation therapy thereby induction of cancer stem cell differentiation may lead to tumor regression. Intestinal normal and cancer organoids represent an ideal model for studying the differentiation process ex vivo. Gene expression profiling of drug-treated organoids can be used for quantification of the differentiation process with high precision. RNA-seq based drug-screening platforms in organoids are not yet established. Here we developed a high-throughput high-content targeted RNA-seq-based platform (TORNADO-seq) for monitoring gene expression of large gene signatures in intestinal organoids which allowed us to quantify and evaluate complex cellular phenotypes and cellular alterations upon drug treatment. We applied TORNADO-seq in drug screening in wt and cancer intestinal organoids. We found many differentiation-inducing drugs in wt organoids, including some drugs specifically enriching for certain cell phenotypes, e.g. enteroendocrine cells. Further, we applied identified differentiation-inducing drugs to cancer organoids (APClof;KRASG12D;TP53lof) and discovered that the majority of those differentiation-inducing drugs also targeted cancer organoids. Differentiation induction seems to be a common mode of action of cancer-targeting drugs. Based on gene expression profiles of treated cancer organoids, we were able to propose and confirm the mechanism of action of several drugs indicating that cancer cells may to be sensitive to alterations in the cholesterol biosynthesis pathway. In general, utilization of TORNADO-seq allows predicting connections between cellular phenotypes and signaling pathways in organoids which can be used for hypothesis generation in a variety of biological systems. The second part of the thesis is devoted to the investigation of mechanisms underlying the accumulation of genetic alterations in CRC tumors. It is not known whether cancer driver genes affect the rate of mutation acquisition. Here we performed exome sequencing of single cell-derived organoids obtained from tumors with either APClof, APClof;KRASG12D or APClof;KRASG12D;TP53lof mutation phenotypes that reflect early stages of CRC development. We discovered that presence of KRAS and P53 mutations didn't affect the number of single nucleotide substitutions (SNSs) in tumors, while the latter was increased in APC mutated tumors compared to wt cells and was highly correlated with the tumor age. P53 inactivation was highly correlated with the presence of large-scale (>10 Mb) copy number alterations (CNAs).

EPFL2021

Immunosuppressive roles of Activin-A in melanoma and characterization of its precursor cleavage

Katarina Pinjusic

Activin-A, a transforming growth factor êµ family member, is a pleiotropic cytokine with diverse functions in development, fertility, adult tissue homeostasis, and aging. Accordingly, deregulation of Activin-A signaling has been associated with many pathological conditions, including cancer and cancer-associated muscle wasting (cachexia). Activin-A was shown to signal in endocrine, but also local autocrine and paracrine manner. Its secretion in many cancer types is associated with a poor prognosis. Previous studies suggest that Activin-A expression in melanoma promotes tumor growth and metastasis indirectly by inhibiting adaptive anti-tumor immunity, leading to a decrease in the intratumoral frequency of cytotoxic CD8+ T cells (CTLs). However, the underlying mechanisms and the relevant direct target cells of Activin-A and their significance for cancer therapies remained unknown. Similar to other TGFêµ-related ligands, proActivin-A is cleaved by proprotein convertases (PCs) to release mature ligands. However, unlike other family members whose signaling is tightly regulated, Activin-A apparently does not have latency.In this thesis, I characterize proActivin-A cleavage and show that one prodomain can be cleaved independently of known PCs. The resulting hemi-cleaved Activin-A can bind activin type II receptors and induce SMAD3 signaling in reporter cells. A protein interactome screen and analysis of cleavage intermediates in plasma revealed that the hemi-cleaved Activin-A likely interacts with extracellular matrix proteins via the remaining prodomain where it promotes local signaling and regulates trafficking. Luciferase reporter assay showed that hemi-cleaved Activin-A can avoid, at least partially, inhibition by endogenous inhibitors FSTL3 and FST, and enable parallel activation of BMP and Activin signaling pathways. Finally, analysis of B16-F1 melanoma models revealed that only fully cleaved Activin-A in source cells increased tumor growth by acting locally in the tumor microenvironment suggesting that the context of Activin-A precursor processing regulates its tumor growth-promoting effect.The second part of this thesis addresses the mechanisms of Activin-induced immunosuppression in melanoma. We found that Activin-A impairs CTL function indirectly and independently of CD4+ T cell, CSF1R+ macrophages, and IL4 signaling. At least in part, anti-tumor CTL responses are impaired by the inhibitory effects of Activin-A on the secretion of critical CTL-recruiting chemokines CXCL9 and CXCL10 by macrophages and dendritic cells (DCs). Furthermore, Activin-A conferred resistance to immune checkpoint blockade therapy. Characterization of Activin-induced changes in the gene expression of tumor-infiltrating cells by Single cell RNA sequencing revealed that INHBA expression induced the most changes in DCs and least in T cells. Interestingly, the most prominently induced hallmark in Activin-secreting tumors across cell types was the IFN signature. In vitro analyses showed that Activin-A increases IFNÎ³-induced activation of STAT1 and confers resistance to cytostatic IFN signaling in cancer cells.Altogether, the findings of this thesis expand our knowledge on the regulation of Activin-A signaling by precursor cleavage and offer insights into mechanisms of Activin-induced immunosuppression in melanoma. Inhibition of Activin-A maturation thus emerges as a potential new strategy to improve responses to immunotherapies in melanoma and likely other cancers