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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