Disulfide-Linked Antibody-Maytansinoid Conjugates: Optimization of In Vivo Activity by Varying the Steric Hindrance at Carbon Atoms Adjacent to the Disulfide Linkage

ImmunoGen, Inc. , 830 Winter Street, Waltham, Massachusetts 02451, United States.
Bioconjugate Chemistry (Impact Factor: 4.51). 03/2011; 22(4):717-27. DOI: 10.1021/bc100480a
Source: PubMed


In this report, we describe the synthesis of a panel of disulfide-linked huC242 (anti-CanAg) antibody maytansinoid conjugates (AMCs), which have varying levels of steric hindrance around the disulfide bond, in order to investigate the relationship between stability to reduction of the disulfide linker and antitumor activity of the conjugate in vivo. The conjugates were first tested for stability to reduction by dithiothreitol in vitro and for plasma stability in CD1 mice. It was found that the conjugates having the more sterically hindered disulfide linkages were more stable to reductive cleavage of the maytansinoid in both settings. When the panel of conjugates was tested for in vivo efficacy in two human colon cancer xenograft models in SCID mice, it was found that the conjugate with intermediate disulfide bond stability having two methyl groups on the maytansinoid side of the disulfide bond and no methyl groups on the linker side of the disulfide bond (huC242-SPDB-DM4) displayed the best efficacy. The ranking of in vivo efficacies of the conjugates was not predicted by their in vitro potencies, since all conjugates were highly active in vitro, including a huC242-SMCC-DM1 conjugate with a noncleavable linkage which showed only marginal activity in vivo. These data suggest that factors in addition to intrinsic conjugate potency and conjugate half-life in plasma influence the magnitude of antitumor activity observed for an AMC in vivo. We provide evidence that bystander killing of neighboring nontargeted tumor cells by diffusible cytotoxic metabolites produced from target cell processing of disulfide-linked antibody-maytansinoid conjugates may be one additional factor contributing to the activity of these conjugates in vivo.

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    • "The fact that epirubicin-(C 3 -amide)-SS-[anti- HER2/neu] also did not exert an enhanced level of cytotoxic anti-neoplastic activity against chemotherapeutic -resistant mammary adenocarcinoma (SKBr-3) may therefore reflect a cell biology related variable that explains a lack of enhanced efficacy. Interestingly, minimal or no correlation frequently exists between the in-vitro and in-vivo potency of covalent immunochemotherapeutics with synthetically introduced disulfide bond structures (Kellogg et al., 2011) which is in marked contrast to covalent immunochemotherapeutics devoid of this same internal chemical structure. Differences in cytotoxic anti-neoplastic potency to this degree in-vivo have been attributed to the influence of hepatic metabolization and variations in the creation of lipophilic and hydrophilic metabolites that determine the extent of distribution within fluid compartments and penetration across intact cancer cell membranes (Erickson et al., 2010) . "

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    • "AMC preparations with stable thioether linkages generally use N-succinimidyl 4-(N-maleimidomethyl ) cyclohexane-1-carboxylate (SMCC) as the linker, with the maytansinoid moiety most commonly being DM1. For disulfide-containing reducible linkages, numerous linker-maytansinoid pairs have been evaluated for AMC preparations with varying degrees of steric hindrance adjacent to the disulfide, either stemming from the linker itself, as in the case of Nsuccinimidyl 4-(2-pyridyldithio)pentanoate (SPP), or from the maytansinoid moiety, as in the case of DM3 and DM4 (Erickson et al., 2006; Lewis Phillips et al., 2008; Kellogg et al., 2011). Erickson et al. (2006, 2010) reported differential in vitro and in vivo processing in mice bearing CanAg-positive COLO 205 tumors of □ S The online version of this article (available at "
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    ABSTRACT: The in vitro characterization of the inhibition potential of four representative maytansinoid species observed upon hepatic and/or tumor in vivo processing of antibody-maytansine conjugates (AMCs) with cleavable and noncleavable linkers is reported. We investigated the free maytansinoid species N(2')-deacetyl-N(2')-(3-mercapto-1-oxopropyl)-maytansine (DM1), (S)-methyl-DM1, and N(2')-deacetyl-N(2')-(4-mercapto-4-methyl-1-oxopentyl)-maytansine (DM4) as representative cleavable linker catabolites and Lysine-N(ε)-N-succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate-DM1 (Lys-MCC-DM1) as the representative noncleavable linker catabolite. Studies with recombinant human cytochromes P450 (P450s) indicate CYP2D6, CYP3A4, and CYP3A5 are the primary isoforms responsible for the oxidative metabolism of DM1, (S)-methyl-DM1, and DM4. Lys-MCC-DM1 was not metabolized by any of the P450 isoforms studied. DM1 was shown to be a reversible inhibitor of CYP2C8 (K(i) = 11 ± 3 μM) and CYP2D6 (K(i) = 14 ± 2 μM). Lys-MCC-DM1 and (S)-methyl-DM1 showed no reversible or time-dependent inactivation of any of the P450s studied. DM1 and DM4 inactivated CYP3A from human liver microsomes with K(i)/k(inact) values of 4.8 ± 0.9 μM/0.035 ± 0.002 min(-1) and 3.3 ± 0.2 μM/0.114 ± 0.002 min(-1), respectively. DM1 and DM4 inactivated recombinant CYP3A4 with K(i)/k(inact) values of 3.4 ± 1.0 μM/0.058 ± 0.005 min(-1) and 1.4 ± 0.3 μM/0.117 ± 0.006 min(-1), respectively. Because of instability in plasma, further characterization of the DM1 and DM4 intramolecular and intermolecular disulfide conjugates observed in vivo is required before an accurate drug-drug interaction (DDI) prediction can be made. AMCs with noncleavable thioether-linked DM1 as the cytotoxic agent are predicted to have no potential for a DDI with any of the major human P450s studied.
    Preview · Article · Jun 2012 · Drug metabolism and disposition: the biological fate of chemicals
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    ABSTRACT: Biodegradability can be incorporated into cationic polymers via use of disulfide linkages that are degraded in the reducing environment of the cell cytosol. In this work, N-(2-hydroxypropyl)methacrylamide (HPMA) and methacrylamido-functionalized oligo-l-lysine peptide monomers with either a non-reducible 6-aminohexanoic acid (AHX) linker or a reducible 3-[(2-aminoethyl)dithiol] propionic acid (AEDP) linker were copolymerized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Both of the copolymers and a 1:1 (w/w) mixture of copolymers with reducible and non-reducible peptides were complexed with DNA to form polyplexes. The polyplexes were tested for salt stability, transfection efficiency, and cytotoxicity. The HPMA-oligolysine copolymer containing the reducible AEDP linkers was less efficient at transfection than the non-reducible polymer and was prone to flocculation in saline and serum-containing conditions, but was also not cytotoxic at charge ratios tested. Optimal transfection efficiency and toxicity were attained with mixed formulation of copolymers. Flow cytometry uptake studies indicated that blocking extracellular thiols did not restore transfection efficiency and that the decreased transfection of the reducible polyplex is therefore not primarily caused by extracellular polymer reduction by free thiols. The decrease in transfection efficiency of the reducible polymers could be partially mitigated by the addition of low concentrations of EDTA to prevent metal-catalyzed oxidation of reduced polymers.
    Full-text · Article · Aug 2011 · International Journal of Pharmaceutics
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