Abstract 4404: Comparative in vivo pharmacokinetic properties of antibody-maytansinoid conjugates with alternative non-cleavable linkers
Authors: Kellogg Brenda , Audette Charlene , Erickson Hans , Mayo Michelle , Okamoto Michael , Pinkas Jan , Sun Xiuxia , Widdison Wayne , Wilhelm Sharon , Chari Ravi , Singh Rajeeva 
Published: February 2011

Abstract
Antibody-maytansinoid conjugates (AMCs) are targeted anticancer agents that deliver a highly potent cytotoxic maytansinoid agent (DM1 or DM4) specifically to tumor cells displaying their target antigen. Multiple AMCs are now in clinical testing for treatment of an array of cancers. AMCs can employ either a reducible (“cleavable”) disulfide linkage or a non-reducible (“non-cleavable”) thioether linkage to tether the thiol-containing maytansinoid agent to the antibody. The most advanced AMC, trastuzumab-DM1 (T-DM1), employs a maleimide based thioether bond made using SMCC (N-succinimidyl-4-(N-maleimido-methyl)-cyclohexane-1-carboxylate) linker to tether DM1 to the trastuzumab antibody.
Given the interest in AMC's with non-cleavable linkers we initiated a study to evaluate alternative non-cleavable antibody-maytansinoid linkages in vivo. This report describes the results of a pharmacokinetic study to evaluate the relative in vivo stability of antibody maytansinoid conjugates with three different non-cleavable linkers: (1) a maleimido-based thioether linkage between the antibody and the thiol-containing maytansinoid DM1 (huC242-MCC-DM1), (2) an iodoacetamido-based thioether linker (huC242-SIA-DM1), or (3) a non sulfur containing link where the maytansinoid is covalently bound directly to the antibody via an amide bond (huC242-Maytansinoid).
The three well characterized conjugates were administered intravenously (10 mg/kg) to CD1 mice and plasma samples were withdrawn via retro-orbital plexus at various time points post injection for determination of concentration of intact conjugate by ELISA methods. The pharmacokinetic data describing conjugate clearance were essentially indistinguishable for all three conjugates, each of which had β phase terminal half-lives of approximately 7.5 days. We did not observe any enhanced instability of the maleimido-based thioether-linked conjugate (huC242-MCC-DM1) compared to the iodoacetamido-based thioether-linked conjugate (huC242-SIA-DM1), as has been reported for auristatin conjugates (Alley et. al. Bioconj. Chem. 2008, 19(3), 759-765). In a separate study, we show that the in vivo half-life of the tritiated conjugate, huC242-MCC-[3H]-DM1, in mouse plasma is similar to the half-life for clearance of total antibody from plasma as measured by ELISA (t1/2,β = 10.5 d vs. 12.6 d, respectively), demonstrating that the huC242-MCC-DM1 conjugate has excellent stability in vivo. We conclude that all three of the non-cleavable conjugate linkages examined here for AMCs (maleimido thioether, acetamido thioether and amide linkage) behave similarly in vivo in terms of plasma stability.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4404.