Stromal expression of long Pentraxin-3 impairs tumor growth and metastasis

Long Pentraxin-3 (PTX3) is a soluble pattern recognition receptor expressed by endothelial and immune cells in inflammatory contexts. We have previously demonstrated that PTX3 binds to different members of the FGF family, thus inhibiting their biological activity. The FGF/FGFR system strongly contributes to cancer progression by inducing tumor growth and neovascularization. To date, recombinant PTX3 protein or PTX3-overexpressing tumor cell lines have been exploited to assess the antitumor effects of this natural FGF trap. Here we generated C57BL/6 transgenic mice expressing human (h)PTX3 under the control of the endothelial specific Tie2/Tek transcription regulatory sequences. These animals were used to investigate the impact of PTX3 overexpression by the host stroma on tumor growth, vascularization and metastasis. Transgenic Tie2-hPTX3 mice were generated by cloning the hPTX3 cDNA into the late-generation, self-inactivating lentiviral vector Tie2p/e to obtain the Tie2-hPTX3 lentiviral transfer vectors that were injected into fertilized oocytes. Expression of the transgene was confirmed by RT-PCR and western blot analyses of different organs from Tie2-hPTX3 mice that showed increased levels of circulating PTX3 (80-180 ng/ml) when compared to wild type (wt) animals (<1.8 ng/ml). Also, histological analysis confirmed the perivascular accumulation of hPTX3 in transgenic animals. To assess the anti-angiogenic activity of endothelium-derived hPTX3, we performed ex vivo aorta ring and in vivo matrigel plug assays. Both assays revealed a significant inhibition of FGF2-driven angiogenesis in Tie2-hPTX3 mice that maintained their responsiveness to VEGF-A, thus confirming the specificity of the effect. Next, different syngeneic FGF-dependent tumor cell lines, including TRAMP-C2 prostate carcinoma, B16-F10 melanoma and Lewis Lung carcinoma cells, were subcutaneously injected in Tie2-hPTX3 mice. Notably, the growth of all tumor grafts was significantly reduced in Tie2-hPTX3 mice when compared to wt animals. Also, histological analysis of TRAMP-C2 tumors grown in Tie2-hPTX3 mice showed a strong perivascular expression of hPTX3 and a significant reduction of FGFR1 phosphorylation. This was paralleled by a significant decrease of tumor vascularity and tumor cell proliferation whereas no difference in tumor growth was observed for TRAMP-C2 grafts expressing a constitutively activated form of FGFR1. Finally, B16-F10 melanoma and M5076 ovarian sarcoma cells showed a dramatic decrease of their capacity to form experimental metastases in the lung and liver, respectively, after intravenous injection in Tie2-hPTX3 mice. PTX3 is a natural FGF ligand trap. Our findings demonstrate for the first time that the production of PTX3 by the host stroma may exert a dramatic impact on tumor growth, vascularization and metastasis with potential exploitation for the therapy of FGF-dependent tumors.