title: Tumor delivery and in vivo processing of disulfide-linked and thioether-linked antibody-maytansinoid conjugates.
abstract: Antibody-drug conjugates (ADCs) are designed to eradicate cancer cells that express the target antigen on their cell surface. A key component of an ADC is the linker that covalently connects the cytotoxic agent to the antibody. Several antibody-maytansinoid conjugates prepared with disulfide-based linkers such as those targeting the CanAg antigen have been shown to display more activity in preclinical mouse xenograft models than corresponding conjugates prepared with uncleavable thioether-based linkers. To investigate how the linker influences delivery and activation of antibody-maytansinoid conjugates, we isolated and characterized the [(3)H]maytansinoids from CanAg-positive tumor tissues following a single intravenous administration of 300 microg/kg (based on maytansinoid dose) of anti-CanAg antibody (huC242)-(3)H-maytansinoid conjugates prepared with cleavable disulfide linkers and an uncleavable thioether linker. We identified three target-dependent tumor metabolites of the disulfide-linked huC242-SPDB-DM4, namely, lysine-N(epsilon)-SPDB-DM4, DM4, and S-methyl-DM4. We found similar metabolites for the less hindered disulfide-linked huC242-SPP-DM1 conjugate with the exception that no S-methyl-DM1 was detected. The sole metabolite of the uncleavable thioether-linked huC242-SMCC-DM1 was lysine-N(epsilon)-SMCC-DM1. The AUC for the metabolites of huC242-SMCC-DM1 at the tumor over 7 d was about 2-fold greater than the corresponding AUC for the metabolites of the disulfide-linked conjugates. The lipophilic metabolites of the disulfide-linked conjugates were found to be nearly 1000 times more cytotoxic than the more hydrophilic lysine-N(epsilon)-linker-maytansinoids in cell-based viability assays when added extracellularly. The cell killing properties associated with the lipophilic metabolites of the disulfide-linked conjugates (DM4 and S-methyl-DM4, and DM1) provide an explanation for the superior in vivo efficacy that is often observed with antibody-maytansinoid conjugates prepared with disulfide-based linkers in xenograft mouse models.
authors.affiliation: ImmunoGen, Inc., Waltham, MA 02451, USA. hans.erickson@immunogen.com
authors.forename: Hans K
authors.initials: HK
authors.lastname: Erickson
authors.forename: Wayne C
authors.initials: WC
authors.lastname: Widdison
authors.forename: Michele F
authors.initials: MF
authors.lastname: Mayo
authors.forename: Kathleen
authors.initials: K
authors.lastname: Whiteman
authors.forename: Charlene
authors.initials: C
authors.lastname: Audette
authors.forename: Sharon D
authors.initials: SD
authors.lastname: Wilhelm
authors.forename: Rajeeva
authors.initials: R
authors.lastname: Singh
mesh_terms: D000818:Animals; D000906:Antibodies / Q000737:chemistry / Q000276:immunology / Q000378:metabolism* / Q000627:therapeutic use; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004220:Disulfides / Q000737:chemistry*; D006801:Humans; D018796:Immunoconjugates / Q000737:chemistry / Q000276:immunology / Q000378:metabolism* / Q000627:therapeutic use*; D008453:Maytansine / Q000737:chemistry / Q000276:immunology / Q000378:metabolism* / Q000627:therapeutic use; D051379:Mice; D016513:Mice, SCID; D009369:Neoplasms / Q000188:drug therapy / Q000276:immunology / Q000378:metabolism*; D013440:Sulfides / Q000737:chemistry*; D023041:Xenograft Model Antitumor Assays
chemical_list: D000906:Antibodies; D004220:Disulfides; D018796:Immunoconjugates; D013440:Sulfides; D008453:Maytansine