Tumor Delivery and in Vivo Processing of Disulfide-Linked and Thioether-Linked Antibody-Maytansinoid Conjugates

Bioconjug Chem. 2010 Jan;21(1):84-92. doi: 10.1021/bc900315y.

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.

MeSH terms

  • Animals
  • Antibodies / chemistry
  • Antibodies / immunology
  • Antibodies / metabolism*
  • Antibodies / therapeutic use
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Disulfides / chemistry*
  • Humans
  • Immunoconjugates / chemistry
  • Immunoconjugates / immunology
  • Immunoconjugates / metabolism*
  • Immunoconjugates / therapeutic use*
  • Maytansine / chemistry
  • Maytansine / immunology
  • Maytansine / metabolism*
  • Maytansine / therapeutic use
  • Mice
  • Mice, SCID
  • Neoplasms / drug therapy
  • Neoplasms / immunology
  • Neoplasms / metabolism*
  • Sulfides / chemistry*
  • Xenograft Model Antitumor Assays

Substances

  • Antibodies
  • Disulfides
  • Immunoconjugates
  • Sulfides
  • Maytansine