Production of a monoclonal antibody-methotrexate conjugate utilizing dextran T-40 and its biologic activity

Methotrexate (MTX), a folate antagonist and anticancer agent, was linked covalently to murine monoclonal anti-HLA IgG1 antibody (H-1) with the use of dextran T-40 as a multivalent carrier. As determined spectrophotometrically, the conjugate was composed of 9.20 mol MTX per 1 mol antibody. Of the substituted MTX, 46.3% (4.30 mol MTX per 1 mol antibody) exhibited inhibitory activity on dihydrofolate reductase. The MTX conjugated to H-1 [MTX-(H-l)] showed significantly stronger cytotoxicity against HLA-bearing cells than cells lacking HLA (p less than 0.001) in cultivation after a 2-hour exposure to the drugs. In the same experiment, free MTX showed equivalent cytotoxicity to cells both bearing and lacking HLA. When cells were cultivated for 3 days with the drugs, MTX-(H-l) also showed significantly stronger cytotoxicity than free MTX or MTX-control IgG conjugate against HLA-bearing cells (p less than 0.001), and the MTX-(H-l), MTX-control IgG, and free MTX showed equivalent cytotoxicity to cells lacking HLA. Our results indicate that the MTX-(H-l) conjugate binds to the cell surface antigen by its antibody action and exerts greater MTX cytotoxicity than free MTX in vitro.