Abstract LB-252: Enzymology of the mechanism of action for MDX-1203 antibody drug conjugate

MDX-1203 is an antibody drug conjugate under clinical evaluation by Bristol-Myers Squibb. The antibody portion is MDX-1115, a fully human anti-CD70 IgG. The drug portion is MED-2460, a small molecule which itself is composed of the releasable prodrug MED-2284, a cleavable di-peptide linker, and a maleimide reactive group intended to facilitate protein attachment. The mechanism of action of MDX-1203 involves tumor specific delivery and cellular uptake of ADC, followed by the intervention of two different enzymatic pathways. Release of prodrug is accomplished through proteolysis of a citruline-valine di-peptide linker, presumably by Cathepsin B activity in the acidic environment of the lysosome. Activation of released prodrug, MED-2284, occurs in the endoplasmic reticulum via esterase cleavage in the of the piperazine protecting group by the enzyme human Carboxylesterase 2. Michaelis Menten methodologies are used to probe activity of each enzymatic pathway and their relative role in the activity of the drug. Proteolysis is investigated through the use of Human Liver Cathepsin B protease. A kinetic model is constructed for a cysteine modified analogue MED-2460, and then applied to the more complex system involving antibody conjugated drug. Enzymatic activation of released prodrug MED-2284 is investigated with recombinant Human Carboxylesterase 2. For each pathway, the kinetic parameters Km, kcat, and enzymatic efficiency are measured and reported. Parameters are compared in an effort to define the enzymatic rate limiting step in the activation MDX-1203, and define their respective roles in the overall activity of the drug. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-252. doi:1538-7445.AM2012-LB-252