Introduction
Angiogenesis is a hallmark of cancer1 and it plays a critical role in tumor development, especially in the proliferation and progression of colorectal cancer (CRC)2,3.
Indeed, tumor vasculature prompts tumor growth and metastasis since it not only provides nutrients and oxygen for the rapid proliferation of cancer cells as well as a route for metastatization, but also affects the infiltration of immune cells to the tumor site. Thus, the targeting of angiogenesis has become an attractive strategy against various human malignancies, including CRC4. In fact, tumor-associated vessels are leaky and poorly efficient due to the dismantlement of the basement membrane and the loss of pericytes, thus preventing proficient drug delivery to the tumor5.
In this context, we demonstrated that Multimerin-2, an extracellular matrix glycoprotein deposited along the blood vessels in juxtaposition between endothelial cells and pericytes, mural cells fundamental in vessels stabilization, is key in the maintenance of vascular homoeostasis6. However, the effects of this molecule on pericytes biology and its putative impact on the immune cells’ recruitment are still poorly understood.
Aims & Methods
Immunohistochemistry analysis on colorectal cancer patients’ biopsies revealed that colon cancer associated vessels display a downregulated expression of Multimerin-2. Thus, we aimed to verify the extent of pericyte recruitment by Multimerin-2-devoid vessels in a colon cancer model and to evaluate how Multimerin-2 loss affects the surrounding tumor microenvironment.
Human umbilical vein endothelial cells (HUVEC) and Human brain vascular pericytes (HBVP) were used as in vitro models for proliferation, functional assays, transcriptomic and proteomics analyses. Wild type and Multimerin-2-/-C57BL/6 mice were subcutaneously injected with the syngeneic colon cancer MC-38 cells and the tumor sections were analysed by immunofluorescence analyses. Animals were then treated with cisplatin six hours prior sacrificing to evaluate the drug delivery.
Results
We demonstrated that Multimerin-2 affects pericytes migration, adhesion, and proliferation. MC-38 xenografts from Multimerin-2-/-mice displayed lower number of pericytes along the vessels as well as increased hypoxia, likely due to vascular inefficiency. The delivery of drug to the tumors was impaired as assessed by the analysis of cisplatin DNA adducts, following the treatment with the chemotherapy drug.
Importantly, tumors from Multimerin-2-/-mice also displayed an altered CD68+ cells infiltrate, suggesting that Multimerin-2 loss can affect macrophages recruitment to the tumor site. These results are in agreement with the finding that Multimerin-2 devoid endothelium was more permissive for the migration of the monocytic cell line THP-1. Finally, the loss of Multimerin-2 also associates with the expression of cytokines involved in macrophages recruitment.
Conclusion
In conclusion, loss of Multimerin-2 in CRC associates with poor pericyte recruitment, compromised delivery of drugs to the tumor, and an altered immune response. Our results suggest that Multimerin-2 expression could represent a promising marker to predict the efficacy of immunotherapy and the outcome of CRC patients.
References
1. Hanahan, D. & Weinberg, R. A. Hallmarks of Cancer: The Next Generation. Cell 144, 646–674 (2011).
2. Weis, S. M. & Cheresh, D. A. Tumor angiogenesis: molecular pathways and therapeutic targets. Nat Med 17, 1359–1370 (2011).
3. Angiogenesis Factors Involved in the Pathogenesis of Colorectal Cancer. Current Health Sciences Journal 5–11 (2013).
4. Rivera, L. B. & Bergers, G. Tumor angiogenesis, from foe to friend. Science 349, 694–695 (2015).
5. Carmeliet, P. & Jain, R. K. Principles and mechanisms of vessel normalization for cancer and other angiogenic diseases. Nat Rev Drug Discov 10, 417–427 (2011).
6. Pellicani, R. et al. Multimerin-2 maintains vascular stability and permeability. Matrix Biology 87, 11–25 (2020).