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P015. The VEGFC/VEGFR3 pathway controls colitis associated cancer formation and progression through lymphangio-genesis and lymphatic endothelial VE-cadherin

C. Tacconi, S. D'Alessio, C. Correale, A. Gandelli, S. Vetrano, S. Danese, Humanitas Research Hospital, IBD Center, Rozzano, Milan, Italy

Background

Chronic intestinal inflammation occurring in Inflammatory Bowel Disease (IBD) predisposes to colitis-associated colorectal cancer (CAC). Tumor-induced lymphangiogenesis is one of the processes taking place in cancer, but no mechanistic data is available on the molecules modulating lymphangiogenesis in CAC. VEGFC is a key player in lymphangiogenesis that signals through its cognate receptor VEGFR3 and its blockade has been used in several models of metastatic cancer. However, little is known about the role played by adherens' junction proteins, such as Vascular Endothelial (VE)-cadherin, on the lymphatic endothelium during the metastatic process. We hypothesized that lymphatics-targeted therapy may be effective in CAC formation and would abate metastasis dissemination by maintaining lymphatic vessel junctions' integrity.

Methods

The azoxymethane (AOM)/dextran sulfate sodium (DSS) CAC model was used. In addition, colitic mice were orthotopically injected with CT26 colon cancer cells. Modulation of lymphangiogenesis was obtained by systemic inhibition of VEGFR3 or adenoviral overexpression of VEGFC. Tumor density and size were measured at the end of the AOM/DSS protocol by visual, endoscopic and histological inspection. In the xenotransplantation model, liver, lung and draining lymphnodes were processed for metastasis quantification by FACS analysis. Whole mounts of colons were stained to analyse area density and dimension of lymphatic vessels (LVs) within peritumoral and tumoral regions. Moreover, VE-cadherin distribution and expression were studied in vivo on LVs and in vitro on Human intestinal lymphatic endothelial cells (HILEC) stimulated with VEGFC or with a VEGFR3 inhibitor.

Results

In both the AOM/DSS and the xenotransplantation models, systemic inhibition of VEGFR3 inhibited lymphangiogenesis in peritumoral and tumoral regions, reducing both area density and LVs dimension. In addition, it reduced tumor density and size, together with an abatement of metastatic dissemination, when compared to untreated animals. In contrast, tumor density and growth, including metastasis formation was enhanced by VEGFC, which in turn increased lymphangiogenesis within the same regions. Whole mount staining showed that VEGFC altered VE-cadherin expression both in vivo and in vitro, whereas VEGFR3 inhibitor kept endothelial junction integrity, thus linking the VEGFC/VEGFR3 pathway to VE-cadherin-dependent metastasis dissemination.

Conclusion

Our findings demonstrate that VEGFC/VEGFR3-dependent lymphangiogenesis plays a key role both in CAC growth and metastasis dissemination. Our study reveals a novel mechanism of control of lymphatic junction integrity which may be a promising target for the treatment of CAC and the associated metastatic process.