[Tetraspanins: a new target for antiangiogenic therapy?]. / Les tétraspanines : une nouvelle cible pour la thérapie anti-angiogénique ?

Inhibition of the vascular endothelial growth factor A or inhibition of its receptors are currently used for the treatment of cancer. However, the results are still modest, especially because of the multitude and redundancy of angiogenic factors. It can be hypothesized that therapies targeting directly endothelial cells themselves could be more effective. The tetraspanins are transmembrane molecules, which are devoid of intrinsic enzymatic activity but can associate with each other and with other molecules such as integrins or proteins of the immunoglobulin superfamily to form a network. The tetraspanins are present on the surface of endothelial cells and in vitro, inhibition of these molecules by antibodies or small interfering RNA suggests that tetraspanins play a role in angiogenesis. These preliminary data have been confirmed by the study of cancer xenografts in tetraspanin-deficient mice, which have a significant decrease in tumor size and tumor angiogenesis. In vivo, it has been shown that intravenous administration of a monoclonal antibody (ALB6) directed against CD9 decreases the tumor growth and angiogenesis and that intravitreal injection of a small interfering RNA decreasing CD9 significantly inhibits choroidal neovascularization induced by laser. Finally, anti-angiogenic effects and potent anti-tumor activity are observed by the intraperitoneal administration of GS-168AT2, a peptide derived from CD9-Partner 1, a molecule belonging to the immunoglobulin superfamily, which interacts strongly with the CD9 and CD81. These data suggest that the pharmacological modulation of the tetraspanin web could play a new promising anti-angiogenic strategy.

A truncated form of CD9-partner 1 (CD9P-1), GS-168AT2, potently inhibits in vivo tumour-induced angiogenesis and tumour growth.

BACKGROUND: Tetraspanins are transmembrane proteins known to contribute to angiogenesis. CD9 partner-1 (CD9P-1/EWI-F), a glycosylated type 1 transmembrane immunoglobulin, is a member of the tetraspanin web, but its role in angiogenesis remains to be elucidated. METHODS: We measured the expression of CD9P-1 under angiogenic and angiostatic conditions, and the influence of its knockdown onto capillary structures formation by human endothelial cells (hECs). A truncated form of CDP-1, GS-168AT2, was produced and challenged vs hEC proliferation, migration and capillaries' formation. Its association with CD9P-1, CD9, CD81 and CD151 and the expressions of these later at hEC surface were analysed. Finally, its effects onto in vivo tumour-induced angiogenesis and tumour growth were investigated. RESULTS: Vascular endothelial growth factor (VEGF)-induced capillary tube-like formation was inhibited by tumour necrosis factor α and was associated with a rise in CD9P-1 mRNA expression (P<0.05); accordingly, knockdown of CD9P-1 inhibited VEGF-dependent in vitro angiogenesis. GS-168AT2 dose-dependently inhibited in vitro angiogenesis, hEC migration and proliferation (P<0.05). Co-precipitation experiments suggest that GS-168AT2 corresponds to the sequence by which CD9P-1 physiologically associates with CD81. GS-168AT2 induced the depletion of CD151, CD9 and CD9P-1 from hEC surface, correlating with GS-168AT2 degradation. Finally, in vivo injections of GS-168AT2 inhibited tumour-associated angiogenesis by 53.4±9.5% (P=0.03), and reduced tumour growth of Calu 6 tumour xenografts by 73.9±16.4% (P=0.007) without bodyweight loss. CONCLUSION: The truncated form of CD9P-1, GS-168AT2, potently inhibits angiogenesis and cell migration by at least the downregulation of CD151 and CD9, which provides the first evidences for the central role of CD9P-1 in tumour-associated angiogenesis and tumour growth.