Therapeutic Potential of an Anti-CD44v6 Monoclonal Antibody in Xenograft Models of Colorectal and Gastric Cancer

CD44 variant (CD44v) isoforms are involved in promoting cancer metastasis, sustaining cancer stem cell (CSC) properties, and conferring resistance to therapeutic interventions. Consequently, the development of monoclonal antibodies (mAbs) targeting CD44v represents a crucial strategy for eliminating CD44v-positive cancer cells. Previously, an anti-CD44v6 mAb, C₄₄Mab-9 (mouse IgG₁, κ), was established. C₄₄Mab-9 recognizes explicitly the epitope encoded by the variant exon 6-encoded region of CD44 and applies to flow cytometry, western blotting, and immunohistochemistry. To assess the therapeutic potential, a mouse IgG_2a isotype of C₄₄Mab-9 (designated C₄₄Mab-9-mG_2a) was generated, and the in vitro and in vivo antitumor activities were evaluated using gastric and colorectal cancer cell lines. C₄₄Mab-9-mG_2a demonstrated specific binding to CD44v3-10-overexpressed Chinese hamster ovary cells (CHO/CD44v3-10), as well as gastric cancer (NUGC-4) and colorectal cancer (COLO201 and COLO205) in flow cytometry. C₄₄Mab-9-mG_2a exerted antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against CHO/CD44v3-10, NUGC-4, COLO201, and COLO205. Moreover, systemic administration of C₄₄Mab-9-mG_2a significantly inhibited tumor growth in CHO/CD44v3-10, NUGC-4, COLO201, and COLO205 xenografts compared with the control IgG_2a. These findings indicate that C₄₄Mab-9-mG_2a could be applied to the mAb-based therapy against CD44v6-positive tumors.