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

• Published in: Bioconjugate chemistry Vol. 21; no. 1; pp. 84 - 92
• Main Authors: Erickson, Hans K, Widdison, Wayne C, Mayo, Michele F, Whiteman, Kathleen, Audette, Charlene, Wilhelm, Sharon D, Singh, Rajeeva
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 20-01-2010
• Subjects: Animals; Antibodies - chemistry; Antibodies - immunology; Antibodies - metabolism; Antibodies - therapeutic use; Antigens; Biochemistry; 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; Rodents; Sulfides - chemistry; Tumors; Xenograft Model Antitumor Assays
• ISSN: 1043-1802; 1520-4812
• DOI: 10.1021/bc900315y

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 [3H]maytansinoids from CanAg-positive tumor tissues following a single intravenous administration of 300 μg/kg (based on maytansinoid dose) of anti-CanAg antibody (huC242)-3H-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 ε-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 ε-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 ε-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.