Work

133 In vitro comparison of the stability and biotransformation of sac-TMT and control antibody-drug conjugates in human plasma

Year: 2026

Type: conference-abstract

Abstract: Background Sacituzumab tirumotecan (sacTMT) is a TROP2-directed antibody–drug conjugate (ADC) currently being developed for multiple common cancers. It employs methylsulfonyl pyrimidine-based conjugation chemistry, enabling an irreversible coupling in the connection between linker-payload and the antibody relative to conventional ADCs. SacTMT also incorporates a pHsensitive connection in the linker–payload designed to enhance stability in circulation and maximize intratumoral payload release via pHdependent cleavage. Here, we evaluated the pHdependent payload release, irreversible coupling moiety of linker-payload to the antibody, and biotransformation of sacTMT alongside sacituzumab govitecan (SG) and trastuzumab vedotin (TRA-V).Methods pHdependent payload release was assessed by quantifying free payload via LC–MS following incubation of sacTMT in buffers across physiologically relevant pH conditions. For biotransformation, sacTMT, SG, and TRA-V were incubated in human plasma for up to 14 days. Biotransformation pathways, DAR reduction, and cysteinetrapped deconjugated linker-payload were studied using immunoaffinity capture followed LC–MS analysis.Results During the pH-dependent payload release assay, sac-TMT payload release increased with longer incubation time and decreasing pH. During plasma incubation, payload mass balance was not observed for TRA-V, indicating that the deconjugated linker-payload binds to albumin via maleimide exchange.In cysteinespiked plasma, sacTMT did not form cysteinyl adducts, whereas SG and TRA-V did. Intact mass analysis confirmed that sacTMT DAR value reduction occurred via linker cleavage (amide hydrolysis), with no evidence of reverse Michael deconjugation, consistent with irreversible coupling to the antibody.In contrast, SG exhibited DAR value reduction and payload release via both linker cleavage and reverse Michael deconjugation. TRA-V showed rapid DAR value reduction with slower payload release, predominantly driven by reverse Michael deconjugation.Conclusions SacTMT was shown to have a unique bifunctional linker in that it combines a pHsensitive connection between linker–payload and has an irreversible coupling between the antibody and linker-payload, enabling controlled payload release. The absence of cysteinetrapped adducts confirms the irreversibility of its coupling to the antibody, distinguishing it from SG and TRA-V, where reverse Michael deconjugation contributes to reduction of the DAR value. Altogether, these data indicate that the sac-TMT linker provides stability in circulation and enables efficient payload release in low pH environments, such as intracellular lysosomes, thereby potentially optimizing tumor targeting and therapeutic index.

Source: Journal for ImmunoTherapy of Cancer

DOI: 10.1136/jitc-2026-sitc2026.0133