A novel therapeutic strategy with anti-CD9 antibody in gastric cancers

CD9 is a member of the tetraspanins, and has been shown to be involved in a variety of cellular activities such as motility, cell signaling, proliferation, adhesion, and metastasis. However, very little is known about the involvement of CD9 in the process of development of primary tumors. In the present study, we investigated whether anti-CD9 monoclonal antibody (ALB6) has antitumor effects in human gastric cancer cell xenografts. Human gastric cancer cell lines (MKN-28) (5 x 10(6) cells/animal) were inoculated subcutaneously into the dorsal region of SCID mice (five mice in each group). After a tumor was visualized, animals were assigned to either the ALB6 treatment group or the control IgG treatment group (100 mu g/body/time, intravenous, three times per week. Day 1, 4, and 7 of first week). Then tumor volumes were monitored every day. Proliferation of tumor was analyzed by 5-bromo-2'-deoxyuridine (BrdU) immunostaining, apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) methods, and angiogenesis was assessed by counting the number of CD34-positive endothelial cells. Tumor volume was significantly suppressed (1,682 +/- A 683 mm(3) versus 4,507 +/- A 1,012 mm(3); P = 0.049), the BrdU labeling indexes were significantly decreased (10.9 +/- A 1.1% versus 17.2 +/- A 1.4%; P = 0.009), the apoptotic indexes were significantly increased (1.98 +/- A 0.48% versus 0.72 +/- A 0.09%; P = 0.034), and tumor microvessel densities were significantly suppressed (671,922 +/- A 34,505 pixels/mm(2) versus 1,135,043 +/- A 36,086 pixels/mm(2); P = 0.037) in the ALB6 treatment group compared with the control IgG treatment group. These results suggest that administration of anti-CD9 antibody to mice bearing human gastric cancer cells successfully inhibits tumor progression via antiproliferative, proapoptotic, and antiangiogenetic effects.