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Summary
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MICROENVIMET is a FP7 granted project built on a network of 9 academic partners from 8 countries.
The participants will combine expertise in genomics, proteomics, bioinformatics, in vivo imaging,
transgenic mice, mouse models of metastasis, genetic manipulation of transplantable tumour cells,
computerized image analysis, virus-mediated gene transfer,
phage display and production of
neutralizing antibodies. This consortium will facilitate shared access to a new microRNA platform,
innovative technologies, human tumour tissue banks, in vivo and in vitro models mimicking
different steps of metastatic dissemination, as well as know how in tumour-host cell interplay,
angiogenesis, lymphangiogenesis, cancer stem cell biology and generation of database.
The MICROENVIMET project proposes innovative approaches for building a comprehensive understanding
of the interplay between cancer cells and their microenvironment both at primary and secondary sites.
The objectives are to identify molecular pathways involved in the regulation of metastatic
dissemination to lung, liver, lymph node and bone. To achieve these objectives, the original
experimental approach proposed is to modulate the production/activity of proteases or their
inhibitors. Proteases are now recognized as key regulators of a complex network of interacting
molecules that modulate the properties of cancer cells and their microenvironment. The project
is intended to identify key molecular pathways underlying early steps of metastatic dissemination
by interfering with the protease network and studying the impact of such experimentally manipulated
microenvironment on metastasis formation. In addition to identifying key regulators of metastasis,
we aim at developing blocking antibodies towards these new candidates, with efficacy for
therapeutic intervention, by using the most advanced state-of-the-art technologies. The study
of cancer stem cells will be integrated into current concepts that consider and attempt to
explain the importance of the microenvironment during cancer progression.
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The Project
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Metastasis is the most serious challenge for cancer treatment. Metastasis still represents
the major death-determinant and causes a significant reduction in the quality of life.
A hallmark of the malignant process is the acquisition of an invasive phenotype that allows
neoplastic cells to invade surrounding tissue and disseminate into specific organs.
The traditionally prevailing explanation of metastasis is that during cancer progression,
tumour cells acquire, through the accumulation of multiple genetic alterations, the ability
to surmount a variety of obstacles including shedding from the primary tumour, entry
(called intravasation) into the blood or lymphatic vessels, survival into circulation,
exit out of the vessels (called extravasation), and growth at a secondary site. For most
carcinomas, progression towards malignancy is accompanied by loss of epithelial differentiation
and a shift towards a mesenchymal phenotype with exacerbated motility and invasiveness.
This epithelial to mesenchymal transition (EMT) is characterized by loss of epithelial markers
such as cadherin and expression of mesenchymal proteins such as for instances vimentin and matrix
metalloprotease-11.
So far, the emphasis has been to reveal the gene expression signatures of primary tumours,
which have been associated with their metastatic potential. Interestingly, these analyses have
hinted at the importance of stroma-related genes, but the significance of the molecular network
and the cell types involved, which determine the susceptibility of distant organs to metastasic
cells is largely unknown. The tumour cell-centered view of the metastatic process has been
recently revisited and the gained information about a variety of cellular and non-cellular
factors in the microenvironment within the primary tumour, support the notion that the
microenvironment is at least as decisive for tumour progression as the intrinsic features
of tumour cells. An additional level of complexity has been provided by studies reporting
on factors secreted by the primary tumours that induce the formation of a pre-metastatic
niche in distant organs, where metastases will ultimately develop.
The tumour microenvironment is a complex ecosystem consisting of cellular and non-cellular
components, where a network of
proteases and protease
inhibitors mediates the signalling
for the respective signature of cellular function. The cellular compartment includes not
only tumour cells but also blood or lymphatic endothelial cells, pericytes, smooth muscle
cells, (myo)fibroblasts, immune and inflammatory cells. In addition, the cellular compartment
also includes a small subpopulation of cancer stem cells (CSC), which are thought to be analogous
to stem cells in normal tissue, dividing both to self-renew and to produce progeny that form
the bulk of the tumour mass. CSC may be the source of metastatic cells as it is hypothesized
that they can easily adopt the invasive genetic programme executed by stem and progenitor
cells during normal organ development.
The non-cellular compartment consists of the various molecules of the extracellular matrix,
whose composition directly and indirectly influences the phenotype of the cellular compartment.
The process of cancer progression and metastatic dissemination is now viewed as a change of the
homeostasis within the tumour microenvironment towards the accumulation of dissemination-promoting
signals at the site of primary tumour formation, as well as in distant organ induced by both
genetic and epigenetic stress.
A. Concept of the present project
Knowledge and control of the immediate microenvironment within the primary tumour, as well
as in the distant organ susceptible to metastases from the primary tumour become as important
as the conventional appreciation of knowledge and control of tumour cells themselves.
In this context, Paget’s concept of tumour cells being seeds that need appropriate soils
(organ environment) to grow and disseminate remains a valid and yet unexplored attractive
concept that requires precise explorations at the molecular level.
In light of this old and underestimated concept, as well as the recent data, our concept
of the process of metastasis clearly needs a major overhaul, and future studies aiming at
understanding and fighting metastasis particularly need to precisely evaluate the contribution
of CSC and the tumour microenvironment in both primary and secondary sites (pre-metastatic niche).
These changes in our view of metastasis will profoundly impact on our understanding of metastatic
dissemination and will have fundamental consequences on the development of new strategies of
cancer treatment and metastasis prevention:
1) CSCs which likely escape the effects of current therapies may represent important targets for
future therapeutic intervention. Investigation of this aspect will then be integrated into current
concepts that attempt to explain and consider the importance of the tumour microenvironment during
the metastatic process and future therapies will aim at increasing the susceptibility of CSCs to medication.
2) Therapeutic modulation of the pre-metastatic niche in the target organ of metastasis may alter
the susceptibility of organs to metastasis so that the devastating progressive spread of tumour
cells can be halted.
The communication between the cellular and non-cellular compartments of the tumour microenvironment
is by large mediated by the so-called protease web. In normal tissue homeostasis, the interacting
network of proteases and their
natural inhibitors maintain a proteolytic balance.
During cancer
progression, this balance is disturbed by overexpression of proteases of (at least) three major
families, proteases (MMPs, ADAM and ADAM-TS), serine proteases, and cysteine proteases (cathepsins).
This imbalance alters the non-cellular compartment, which in turn activates downstream effector
molecules leading to the establishment of a milieu permissive for tumour progression, invasion and
dissemination. Recently, two MMPs (MMP1 and MMP2) have been identified as members of a lung
metastasis gene signature for human breast cancer, playing a key role in vascular remodelling
promoting metastatic progression. In addition, of interest is the finding that the regulation
of the expression of gene clusters can be mediated by microRNA,
a family of small non
coding RNAs which have been recognized as key regulators of development and cell fate determination.
Profiling these regulatory elements should allow the identification of gene-repertoires modulated
simultaneously at specific steps of cancer metastasis.
B. Objectives
Our original experimental approach aims at elucidating early mechanisms of metastatic dissemination
by modulating the production or activities of proteases (metalloproteases, serine proteases and
cysteine cathepsins) both in primary and secondary sites. Proteases are key regulators of a
so-called protease web, a complex network of interacting molecules that modulates the properties
of cancer cells and CSCs as well as permissive feature of their microenvironment.
Any interference with a protease (gene deletion, overexpression, inhibition) has a profound
impact on interacting proteins leading to the modification of the tumour microenvironment
and tumour phenotype (Figure 1). The proposal is intended to identify key molecular pathways
which are fundamental for early steps of metastatic dissemination in both entities (primary
tumour and target organ of metastasis). This will be achieved by investigating the susceptibility
of the experimentally manipulated microenvironment to metastasis. We will focus our interest on
how primary tumours influence the elaboration of a permissive pre-metastatic niche. The validity
of an identified target in primary tumours will be assessed on human samples issued from tumour
banks available in the Consortium in order to evaluate possibilities for therapeutic intervention.
Figure 1: Innovative aspects and relevance to the proposal. The proposal aims at building a
comprehensive understanding of the interplay between
cancer cells,
cancer stem cells (CSC) and
their microenvironment, both at primary and secondary sites, in pre- and post-metastatic phases.
Modulation of tumour microenvironment will be achieved by interfering with
proteases which are
central mediators of a complex molecular network, as well as key regulators of various cell functions.
In addition to this innovative experimental approach, the present project aims at investigating the
contribution of microRNA during
early steps of metastatic dissemination by exploiting a microRNA platform
set up by one partner. Since microRNAs regulate the expression of clusters of genes, microRNA profiling
should allow the identification of gene- repertoires modulated at specific steps of
cancer metastasis.
The development of novel therapeutic strategies to fight metastasis is dependent upon pinpointing
molecules that are responsible for initiating and promoting metastatic dissemination of malignant cells.
The objective of this collective research project is to build a comprehensive understanding of the
interplay between cancer cells and their microenvironment, both at primary and secondary sites, and to
identify possible therapeutic target molecules/pathways.
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