Specific Inhibition of the VEGFR-3 Tyrosine Kinase by SAR131675 Reduces Peripheral and Tumor Associated Immunosuppressive Myeloid Cells.

Myeloid derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) represent prominent components in cancer progression. We previously showed that inhibition of the VEGFR-3 pathway by SAR131675 leads to reduction of TAM infiltration and tumor growth. Here, we found that treatment with SAR131675 prevents the accumulation of immunosuppressive blood and splenic MDSCs which express VEGFR-3, in 4T1 tumor bearing mice. Moreover we showed that soluble factors secreted by tumor cells promote MDSCs proliferation and differentiation into M2 polarized F4/80+ macrophages. In addition, cell sorting and transcriptomic analysis of tumor infiltrating myeloid cells revealed the presence of a heterogeneous population that could be divided into 3 subpopulations: (i) immature cells with a MDSC phenotype (GR1+/CD11b+/F4/80-); (ii) "immuno-incompetent" macrophages (F4/80high/CD86neg/MHCIILow) strongly expressing M2 markers such as Legumain, CD206 and Mgl1/2 and (iii) "immuno-competent"-M1 like macrophages (F4/80Low/CD86+/MHCIIHigh). SAR131675 treatment reduced MDSCs in lymphoid organs as well as F4/80High populations in tumors. Interestingly, in the tumor SAR131675 was able to increase the immunocompetent M1 like population (F4/80low). Altogether these results demonstrate that the specific VEGFR-3 inhibitor SAR131675 exerts its anti tumoral activity by acting on different players that orchestrate immunosuppression and cancer progression in a tumoral context: MDSCs in peripheral lymphoid organs and TAMs infiltrating the tumor.

SAR131675, a potent and selective VEGFR-3-TK inhibitor with antilymphangiogenic, antitumoral, and antimetastatic activities.

SAR131675 is a potent and selective VEGFR-3 inhibitor. It inhibited VEGFR-3 tyrosine kinase activity and VEGFR-3 autophosphorylation in HEK cells with IC(50) values of 20 and 45 nmol/L, respectively. SAR131675 dose dependently inhibited the proliferation of primary human lymphatic cells, induced by the VEGFR-3 ligands VEGFC and VEGFD, with an IC(50) of about 20 nmol/L. SAR131675 was found to be highly selective for VEGFR-3 versus 107 receptors, enzymes, ion channels, and 65 kinases. However, it was moderately active on VEGFR-2 with a VEGFR-3/VEGFR-2 ratio of about 10. SAR131675 had no antiproliferative activity on a panel of 30 tumors and primary cells, further showing its high specificity and indicating that SAR131675 is not a cytotoxic or cytostatic agent. SAR131675 was very well tolerated in mice and showed a potent antitumoral effect in several orthotopic and syngenic models, including mammary 4T1 carcinoma and RIP1.Tag2 tumors. Interestingly, it significantly reduced lymph node invasion and lung metastasis, showing its antilymphangiogenic activity in vivo. Moreover, treatment of mice before resection of 4T1 primary tumors was sufficient to prevent metastasis. Tumor-associated macrophages (TAM) play an important role in tumor growth and metastasis. The expression of VEGFR-3 on TAMs has been recently described. F4/80 immunostaining clearly showed that SAR131675 significantly reduced TAM infiltration and aggregation in 4T1 tumors. Taken together, SAR131675 is the first highly specific VEGFR-3-TK inhibitor described to date, displaying significant antitumoral and antimetastatic activities in vivo through inhibition of lymphangiogenesis and TAM invasion.

Neuropilin-2 interacts with VEGFR-2 and VEGFR-3 and promotes human endothelial cell survival and migration.

Neuropilin 2 (NRP2) is a receptor for the vascular endothelial growth factor (VEGF) and the semaphorin (SEMA) families, 2 unrelated ligand families involved in angiogenesis and neuronal guidance. NRP2 specifically binds VEGF-A and VEGF-C, although the biological relevance of these interactions in human endothelial cells is poorly understood. In this study, we show that both VEGF-A and VEGF-C induce the interaction of NRP2 with VEGFR-2. This interaction correlated with an enhancement of the VEGFR-2 phosphorylation threshold. Overexpression of NRP2 in primary human endothelial cells promoted cell survival induced by VEGF-A and VEGF-C. In contrast, SEMA3F, another ligand for NRP2, was able to inhibit human endothelial cell survival and migration induced by VEGF-A and VEGF-C. Moreover, a siRNA targeting specifically NRP2 was a potent inhibitor of human endothelial cell migration induced by VEGF-A and VEGF-C. Thus, our data indicate that NRP2 acts as a coreceptor that enhances human endothelial cell biological responses induced by VEGF-A and VEGF-C.

Heterodimerization with vascular endothelial growth factor receptor-2 (VEGFR-2) is necessary for VEGFR-3 activity.

VEGFR-3 is essential for vascular development and maintenance of lymphatic vessel's integrity. Little is known about its cooperative effect with other receptors of the same family. Contrary to VEGFR-2, stimulation of VEGFR-3 by VEGF-C and -D failed to enhance its phosphorylation either in HEK293T or in PAE cells. These ligands were unable to induce angiogenesis of PAEC expressing VEGFR-3 alone. In the presence of VEGFR-2, VEGF-C and -D induced heterodimerization of VEGFR-3 with VEGFR-2. This heterodimerization was associated with enhanced VEGFR-3 phosphorylation and subsequent cellular responses as evidenced by the formation of capillary-like structures in PAE cells and proliferation of primary human endothelial cells expressing both receptors. Taken together, these results show for the first time that VEGFR-3 needs to be associated to VEGFR-2 to induce ligand-dependent cellular responses.