Introduction
Tumor angiogenesis is considered as a hallmark of cancer1 and plays a critical role in colorectal cancer (CRC) development and progression2,3. Tumor vasculature promotes 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. Since, many vessels associated with CRC lose Multimerin-2 expression, thus we aimed at verifying the effects of this loss in pericyte recruitment, vascular stability, and the surrounding tumor microenvironment.
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 at verifying the extent of pericyte recruitment by Multimerin-2-devoid vessels in a colon cancer model and at evaluating 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 pericyte coverage and microenvironmental features were assessed in tumor sections by immunofluorescence as well as drug delivery following cisplatin treatment six hours prior sacrifice.
Results
We demonstrated that Multimerin-2 promotes pericytes migration, adhesion, and proliferation. Consistently, MC-38 xenografts from Multimerin-2 mice displayed a decreased pericytes coverage along the vessels as well as increased intratumoral hypoxia, suggestive of vascular inefficiency. In fact, upon treatments we counted less DNA \cisplatin adducts in tumors from Multimerin-2-/- mice. Interestingly, 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. Accordingly, a higher number of the monocytic-like cells THP-1 migrated through a Multimerin-2-depleted endothelium. Furthermore, we observed that the loss of Multimerin-2 also associates with the expression of cytokines involved in macrophages recruitment.
Conclusion
These results suggest that Multimerin-2 loss impairs the pericyte recruitment, adhesion and proliferation. As a result, the vasculature lacking Multimerin-2 is utterly destabilized leading to increased intratumoral hypoxia and poorly efficient drug delivery. Importantly, the absence of Multimerin-2 also impairs the immune response suggesting that different Multimerin-2 expression in CRC tumor associated vessels could represent a promising biomarker to predict the efficacy of chemotherapy and/or immune therapy in CRC patient treatment
References
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