Antibody-Maytansinoid Conjugates Are Activated in Targeted Cancer Cells by Lysosomal Degradation and Linker-Dependent Intracellular Processing

Abstract

Antibody-drug conjugates are targeted anticancer agents consisting of a cytotoxic drug covalently linked to a monoclonal antibody for tumor antigen-specific activity. Once bound to the target cell-surface antigen, the conjugate must be processed to release an active form of the drug, which can reach its intracellular target. Here, we used both biological and biochemical methods to better define this process for antibody-maytansinoid conjugates. In particular, we examined the metabolic fate in cells of huC242-maytansinoid conjugates containing either a disulfide linker (huC242-SPDB-DM4) or a thioether linker (huC242-SMCC-DM1). Using cell cycle analysis combined with lysosomal inhibitors, we showed that lysosomal processing is required for the activity of antibody-maytansinoid conjugates, irrespective of the linker. We also identified and characterized the released maytansinoid molecules from these conjugates, and measured their rate of release compared with the kinetics of cell cycle arrest. Both conjugates are efficiently degraded in lysosomes to yield metabolites consisting of the intact maytansinoid drug and linker attached to lysine. The lysine adduct is the sole metabolite from the thioether-linked conjugate. However, the lysine metabolite generated from the disulfide-linked conjugate is reduced and S-methylated to yield the lipophilic and potently cytotoxic metabolite, S-methyl-DM4. These findings provide insight into the mechanism of action of antibodymaytansinoid conjugates in general, and more specifically, identify a biochemical mechanism that may account for the significantly enhanced antitumor efficacy observed with disulfide-linked conjugates. (Cancer Res 2006; 66(8): 4426-33)

Anetumab Ravtansine: A Novel Mesothelin-Targeting Antibody–Drug Conjugate Cures Tumors with Heterogeneous Target Expression Favored by Bystander Effect

“…MF-T was conjugated to the maytansinoid DM4 via a hindered disulfide linker (SPDB) at ImmunoGen, following published procedures (32)(33)(34). An average drug to antibody ratio of 3.2 was achieved, which is in agreement with the previously described optimal range of 2 to 4 (35).…”

“…Once BAY 94-9343 is bound and internalized by a tumor cell, degradation of the BAY 94-9343 disulfide-based linker releases a cell permeable toxophore metabolite with bystander killing potential (33). This bystander effect was demonstrated, for the first time in vivo, using a xenograft model with different proportions of mesothelin-positive and -negative cells within the inoculated tumors.…”

Antibody-drug conjugates targeted to CD79 for the treatment of non-Hodgkin lymphoma

“…Typically, the drug to antibody ratio was between 2.5 and 4.5. Although the linker after conjugation is MCC, these ADCs are described in other publications as Antibody-SMCC-DM1, 19,20 we describe them here as MCClinked ADCs to more accurately reflect the chemical structure.…”

La montée en puissance des immunoconjugués en oncologie

“…L'antigène peut être dégradé dans le lysosome (4a) ou recyclé à la membrane plasmique (4b). L'agent cytotoxique est ensuite libéré dans le cytosol de la cellule tumorale sous la forme de métabolites dont la composition dépend de l'agent de liaison (5) [25][26][27]. Les métabolites peuvent alors inhiber la polymérisation de la tubuline (6a) ou induire des cassures double brin de l'ADN après migration au noyau (6b), ce qui conduit à l'arrêt du cycle cellulaire, puis à la mort par apoptose.…”