Traditionally, anti-cancer therapies focus on eliminating cancer cells, viewing them as the core of the problem. While this remains true, we can now consider cancers an elaborate ecosystem. Diseased cells develop in a complex environment known as the tumor microenvironment (TME). In cancer research, this area has become central in the ongoing search for improved therapies.
As a critical component of the TME, tumor stroma comprises:
Non-cancerous cells of the connective tissue, including mesenchymal stromal cells, cancer-associated fibroblasts (CAFs) and other mesenchymal cells.
An extracellular matrix (ECM) deposited by these stromal cells. The tumor stroma regulates tumorigenesis, metastasis and sensitivity/resistance to anti-cancer therapies.
As a result of these latest insights, leading pharmaceutical and biotech companies are now focusing on novel treatment strategies which involve and target the TME (Link). Moreover, international scientific conferences are increasingly attracting researchers from academia and industry to present and discuss the latest results obtained from stroma cell targeting (Link).
Below, you will find an overview of the tumor stroma components and the differences between non-malignant and tumor stroma. We will also briefly describe the main strategies under investigation to target tumor stroma, along with how our 3DProSeed StromaLine technology contributes to this cutting-edge research.
What is a tumor stroma and how is it different from a non-malignant stroma?
The cells of connective tissue that specialize in maintaining and remodeling tissue structure include fibroblasts, mesenchymal stromal cells (MSCs), chondrocytes and osteoblasts. These cells and their ECM constitute the stroma of a tissue.
Cancer research scientists often use a broader definition of stroma – as do we at Ectica in our StromaLine product description – that also includes endothelial cells, adipocytes and immune cells. On the other hand, others point out that these cells are not stromal components, despite being part of the TME and influencing tumor progression. Nonetheless, as we see it, the critical questions are: why is tumor stroma different from that of healthy, i.e., non-malignant tissue? How can this difference direct our research work?
As tumors develop, tell-tale changes occur in the essence of the neighboring stroma. This process, sometimes referred to as activation, creates a fibrotic stroma in which fibroblasts (also called myofibroblasts or CAFs) proliferate. They migrate, secrete more of their ECM than usual and of a different protein composition.
Note: we will cover CAFs and ECM in more detail elsewhere.
These changes generally result in a reorganized and more rigid microenvironment, thus influencing various aspects of tumorigenesis and pharmacology. For instance, research reports suggest that CAFs modulate cancer progression and metastasis by remodeling the ECM. These changes impact the access of anti-cancer drugs and immune cells to the tumor site.
Cells in the tumor stroma also remodel the tumor ECM and secrete elements that lead to the generation of tracks that support cancer cell invasion. Additionally, they produce growth factors and influence angiogenesis, which then supplies nutrients to the tumor and enables dissemination.
Consequently, research now focuses on functionally characterizing these stromal cells. Their role in promoting or suppressing various aspects of tumor progression depends on their tissue origin and sub-types, particularly population heterogeneity.
We should note that tumor-stroma interactions also play a crucial role in chemoresistance and the initiation of blood cancers. By modifying the bone marrow stroma in mouse models (either at the endothelial or mesenchymal level), researchers observed the initiation of myeloproliferative syndromes that may precede leukemia. Logically, elucidating tumor stroma interactions will likely contribute to discovering therapeutic targets and biomarkers for the early detection of cancer.
What are the main strategies to target the tumor stroma?
When we consider the typical mechanism of action of anti-cancer treatment, we tend to think of eliminating the cancer cells either via a cytotoxic effect of the drug or the complex stimulation of the immune system, i.e., immunotherapies. In contrast, numerous trials are now investigating strategies to modulate the tumor stroma, combined with anti-cancer drugs that boost the efficacy of this intervention.
One possible approach is to target the abnormal ECM in the TME by decreasing or inhibiting over-expressed ECM components and normalizing their presence. Prominent examples are the targeting of lysyl oxidase (LOX), which is responsible for cross-linking collagen.
Other strategies involve the degradation of hyaluronic acid and the interference with the fibrotic signaling pathways. In particular, a frequently reported challenge is the risk of interference with the ECM processes necessary for homeostasis in healthy tissues.
A second strategy is to target CAFs because extensive CAF presence correlates with poor prognosis and chemoresistance. Similarly, high levels of fibroblast activation protein (FAP), expressed explicitly by CAFs, are a marker for poor prognosis in certain cancers and a target for their elimination.
As well as eliminating CAFs, researchers seek to revert the fibroblastic activated status to a quiescent level – via TGF-β signaling interference, for instance. At the same time, they want to suppress CAF-derived pro-tumorigenic signaling.
The complexity of this research derives from the heterogeneous CAF phenotypes showing contradictory pro- and anti-tumorigenic functions. For this reason, massive efforts are underway to characterize stromal cell populations of the TME.
Another essential strategy is to target the communication between the perivascular niche, endothelial and mesenchymal cells with blood cancer cells. Not least, the crosstalk between endothelial cells in the bone marrow and leukemia cells contributes to chemoresistance. Furthermore, research in mouse models has proved that the therapeutic blocking of endothelial molecules involved in this process prolongs survival.
Why is 3DProSeed® StromaLine particularly useful in this research?
Ectica Technologies has developed a collection of high-content screening (HCS) compatible primary human stromal models. These stromal cells are cultured in 3D synthetic, animal-free pre-cast hydrogels in 96-well imaging plates (3DProSeed StromaLine collection). As a result, the models come guaranteed to develop according to specifications, using the supplied materials and recommended methods.
Stromal cells currently available include primary human CAFs – standard or expanded – from melanoma, the lungs, pancreas and colon. Basic patient annotations are pre-tested to form αSMA-positive fibroblastic networks in this innovative 3D hydrogel system. Importantly, rigidity levels are fine-tuned and optimal for stromal cell growth.
At Ectica, we remain committed to continuing the characterization of cellular markers and the matrisome. The latest synthetic hydrogel substrates enable the study of the secretion and deposition of endogenous proteins in the TME. Such studies would be notably more complex with animal protein matrices.
In some instances, we offer the possibility to source adenocarcinoma cells, patient-matched to stromal cells. However, if this option is not possible, our CAF matrices still represent an excellent platform to establish tumor stroma co-cultures with non-autologous cancer cells.
We also offer immortalized and GFP-labelled human bone marrow stroma models comprising primary bone marrow MSCs and bone-marrow endothelial cells. These suit co-culture laboratory work with adenocarcinoma cells and various blood cancer cells.
The 3DProSeed® Stromaline series comes with a pre-developed and characterized mesenchymal stromal matrix. Specifically, the product comprises primary stromal cells, optimized hydrogel culture plates, culture media and reagents.
This material originates from adipose tissue or bone marrow in the case of multipotent stromal cells (MSCs) or tumor tissue excisions in the case of CAFs. Once cultured, these stromal cells deposit and remodel extracellular matrix components, secrete signaling molecules and engage in crosstalk with cancer cells.
Summary
In conclusion, Ectica 3DProSeed® is ideal for investigating the role of the stroma in regulating tissue-specific cell behavior such as paracrine signaling, tissue regeneration, tumor growth, metastasis and collective migration models. Crucially, 3DProSeed® facilitates cancer drug screenings in organotypic human models. It is now possible to conduct experiments in the presence of the stromal compartment with minimal adaptation to your existing workflows.
Ectica 3DProSeed® Stromaline hydrogels do not contain animal-derived ingredients.
