An Anti-α-Fetoprotein Antibody-Daunorubicin Conjugate With a Novel Poly-l-glutamic Acid Derivative as Intermediate Drug Carrier

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Abstract
In studies on antitumor antibody-cytotoxic drug conjugates as potential antitumor agents with improved tumor specificity, daunorubicin [(DM) daunomycin] was conjugated with an affinity-purified horse antibody to rat α-fetoprotein (AFP) with a novel derivative of poly-l-glutamic acid (PLGA) as the intermediate drug carrier. A single masked thiol group first was introduced by PLGA, and the thiol group was generated from it after the linking of DM to PLGA at the carboxyl groups of PLGA. The thiol group was used selectively for binding PLGA-DM to antibody that had been modified so as to have the maleimide groups. The conjugates (DM:PLGA:immunoglobulin molar ratio, 19.6:2.8:1 or 11.8:1.1:1) were more potent than DM in in vitro cytotoxicity against the AFP-producing rat ascites hepatoma cell line AH66. In therapeutic experiments, the conjugates were more efficacious in prolonging the lives of AH66 hepatoma-bearing DONRYU rats than DM, antibody, a mixture of DM and antibody, or a conjugate similarly prepared with normal horse immunoglobulin.