Resumen de Icam-1 and mannose receptor expressed on the liver sinusoidal endothelium modulate the local immune response and the development of experimental metastasis of c26 colorectal cancer to the liver
Colorectal cancer (CRC) is one of the most prevalent cancers worldwide. Liver metastasis of CRC is, indeed, a very complex scenario that decreases substantially the prognosis of this disease, been the major cause of CRC related deaths. During liver colonization of metastatic cancer cells, adhesion molecules of both cancer and liver sinusoidal endothelial cells play a major role, allowing cells to adhere and invade the tissue. Liver immune system, immunosupressed by tumor cells, act as a tumor growth supporter, favoring a prometastatic microenvironment. In order to put some light on this process, we analyzed the involvement of tumor LFA-1 integrin and endothelial ICAM-1 interaction during liver metastasis, and its involvement in the immune system regulation, mediated by endothelial Mannose receptor. For that purpose, the LFA-1/ICAM-1 interaction was partially blocked by ß2 integrin deficient C26 cell line and by silencing endothelial ICAM-1, by siRNAs.Results extracted from this project revealed impaired in vitro prometastatic features of ß2 deficient colorectal C26 cancer cells, reporting decreased adhesion to LSECs and collagen, along with significant reduction in migration and proliferation. The partial inhibition of the LFA-1/ICAM-1 interaction (by both methods, ß2 integrin deficient cell line or ICAM-1 silencing in LSECs) drove to dropped cancer cell adhesion to endothelial cells in vitro, accompanied by decreased C26 transendothelial migration. Regarding to immune response modulation, the blockage of this interplay resulted in decreased lymphocyte immunotolerance promoted by tumor activated endothelial cells. In other words, lymphocytes were not immunosuppressed by tumor activated endothelial cells when LFA-1/ICAM-1 was abrogated, probably because mannose receptor mediated endocytosis was not increased, as observed by mannan internalization and DQ-OVA processing by tumor activated LSECs.In vivo liver metastasis assays allowed us confirm previous findings, since cancer cell retention in liver sinusoids 24 hours after tumor cell injection revealed a significant decrease in adhered cells when LFA-1/ICAM-1 interaction was partially inhibited. Immune cell recruitment to these livers was also found to be dropped, compared to C26 bearing control mice. With respect to metastatic development 14 days after tumor cell injection, liver with abrogated LFA-1/ICAM-1 interaction showed significant decrease in tumor area, as well as metastatic foci. This reduction in liver colonization was linked with lower immune cell counts, since CD4+ and CD8+ lymphocytes, along with myeloid derived CD11b+, Gr1+ and CD11b+F4/80+ cell numbers were found to be decreased. Consistently, the expression of prometastatic genes like IL-1ß, COX-2, ICAM-1, ManR, VEGF and IL-10 was downregulated in these mice liver. The better status of these mice was confirmed by MMP-9 activity in portal blood serum, which was reported to be also decreased.These data support our hypothesis, where LFA-1/ICAM-1 interaction arises as one of the ways cancer cells not only invade the liver, but also to receive the required immune cell support to further colonize the organ. Our results reveal the involvement of this interaction during cancer cell adhesion to the liver, as well as its collaboration recruiting immunosuppressive cell populations that will create an immunotolerant microenvironment that will favor liver metastasis. Therefore, tumor LFA-1, and more importantly, host endothelial ICAM-1 emerge as potential molecular therapeutic targets for the treatment of colorectal cancer liver metastasis, from its very early stage.
