Therapeutic targeting of soluble CD146/MCAM with the M2J-1 monoclonal antibody prevents metastasis development and procoagulant activity in CD146-positive invasive tumors.

Initially discovered in human melanoma, CD146/MCAM is expressed on many tumors and is correlated with cancer progression and metastasis. However, targeting CD146 remains challenging since it is also expressed on other cell types, as vessel cells, where it displays important physiological functions. We previously demonstrated that CD146 is shed as a soluble form (sCD146) that vectorizes the effects of membrane CD146 on tumor angiogenesis, growth and survival. We thus generated a novel monoclonal antibody, the M2J-1 mAb, which specifically targets sCD146, but not membrane CD146, and counteracts these effects. In our study, we analyzed the effects of sCD146 on the dissemination and the associated procoagulant phenotype in two highly invasive human CD146-positive cancer cell lines (ovarian and melanoma). Results show that sCD146 induced epithelial to mesenchymal transition, favored the generation of cancer stem cells and increased the membrane expression of tissue factor. Treatment of cancer cells with sCD146 in two experimental models (subcutaneous xenografting and intracardiac injection of cancer cells in nude mice) led to increased tumor dissemination and procoagulant activity. The M2J-1 mAb drastically reduced metastasis but also procoagulant activity, in particular by decreasing the number of circulating tumor microparticles, and blocked the relevant signaling pathways as demonstrated by RNA expression profiling experiments. Thus, our findings demonstrate that sCD146 mediates important pro-metastatic and procoagulant effects in two CD146-positive tumors. Targeting sCD146 with the newly generated M2J-1 mAb could constitute an innovative strategy for preventing dissemination and thromboembolism in many CD146-positive tumors.

Expression of the Neuroblastoma-Associated ALK-F1174L Activating Mutation During Embryogenesis Impairs the Differentiation of Neural Crest Progenitors in Sympathetic Ganglia.

Neuroblastoma (NB) is an embryonal malignancy derived from the abnormal differentiation of the sympathetic nervous system. The Anaplastic Lymphoma Kinase (ALK) gene is frequently altered in NB, through copy number alterations and activating mutations, and represents a predisposition in NB-genesis when mutated. Our previously published data suggested that ALK activating mutations may impair the differentiation potential of neural crest (NC) progenitor cells. Here, we demonstrated that the expression of the endogenous ALK gene starts at E10.5 in the developing sympathetic ganglia (SG). To decipher the impact of deregulated ALK signaling during embryogenesis on the formation and differentiation of sympathetic neuroblasts, Sox10-Cre;LSL-ALK-F1174L embryos were produced to restrict the expression of the human ALK-F1174L transgene to migrating NC cells (NCCs). First, ALK-F1174L mediated an embryonic lethality at mid-gestation and an enlargement of SG with a disorganized architecture in Sox10-Cre;LSL-ALK-F1174L embryos at E10.5 and E11.5. Second, early sympathetic differentiation was severely impaired in Sox10-Cre;LSL-ALK-F1174L embryos. Indeed, their SG displayed a marked increase in the proportion of NCCs and a decrease of sympathetic neuroblasts at both embryonic stages. Third, neuronal and noradrenergic differentiations were blocked in Sox10-Cre;LSL-ALK-F1174L SG, as a reduced proportion of Phox2b+ sympathoblasts expressed ßIII-tubulin and almost none were Tyrosine Hydroxylase (TH) positive. Finally, at E10.5, ALK-F1174L mediated an important increase in the proliferation of Phox2b+ progenitors, affecting the transient cell cycle exit observed in normal SG at this embryonic stage. Altogether, we report for the first time that the expression of the human ALK-F1174L mutation in NCCs during embryonic development profoundly disturbs early sympathetic progenitor differentiation, in addition to increasing their proliferation, both mechanisms being potential crucial events in NB oncogenesis.