Abstract 1794: Preclinical development of TGW101, a first in class click-cleavable ADC with MMAE against non-internalizing pan-carcinoma marker TAG72

Abstract Current ADCs typically rely on intracellular drug release. However, the number of suitable internalizing receptors in solid cancers is limited while there are suitable non-internalizing tumor markers, provided effective extracellular cleavage can be achieved. To expand the ADC target scope, Tagworks is pioneering a radically new approach to ADCs based on its Click-to-Release platform, which centers on selective payload release from a trans-cyclooctene (TCO) linker upon click reaction with a tetrazine molecule (the trigger). In this approach, following tumor accumulation and blood clearance of the click-cleavable ADC, a tetrazine trigger molecule is administered i.v. that rapidly releases the payload from the extracellular ADC, allowing it to distribute into surrounding cells, maximizing the bystander effect. The first in class click-cleavable ADC therapy TGW101 combines a tetrazine trigger (TRG001) with a click-cleavable ADC, TGW101-ADC, targeting non-internalizing tumor marker TAG72, expressed by many adenocarcinomas. The ADC comprises a 60 kD diabody, site specifically conjugated with TCO-linked MMAE at a drug to antibody ratio of 3.8. TGW101 uses a new TCO / tetrazine combination with 100-fold higher reactivity than in previous versions, allowing markedly lower trigger doses, as low as 3 mg/kg, for complete ADC conversion in mice. The purpose of this study was to characterize the anticancer activity of TGW101, and its tolerability and pharmacokinetics (PK) in the rat and non-human primate (NHP). In vitro, TGW101-ADC showed fast and quantitative release of MMAE upon reaction with TRG001. Cell killing was dependent on binding to TAG72 on the cell and extracellular reaction with TRG001. In vivo, TGW101 gave high and stable free intratumor MMAE concentrations (300 nM at 2 mg/kg ADC) and showed strong dose dependent activity in several TAG72-positive xenografts in single and repeated cycles, using a 2-day interval between TGW101-ADC and TRG001, without TGW101-related toxicity. TGW101-ADC alone was stable and very well tolerated in NHPs at repeated doses at 50 mg/kg (NOAEL) with a clearance half-life of 25h. Similarly, TRG001 was very well tolerated, with HNSTD/NOAEL of 700 mg/kg and 300 mg/kg in rat and NHP, respectively, with a half-life of 0.6h in NHP. When used in combination in NHPs, biweekly cycles of ADC followed 4 days later by a high dose of trigger (75 mg/kg) afforded an HNSTD of 5 mg/kg for TGW101-ADC (which equates to 12.5 mg/kg for mAb size), with reversible and non-adverse effects consistent with free MMAE released from residual circulating ADC by Trigger. In conclusion, TGW101 demonstrated potent and specific in vitro and in vivo anti-tumor activity, while it was well tolerated in rats and NHPs at doses at or higher than current MMAE ADCs. This warrants clinical development of this promising click-cleavable ADC with the aim to expand the ADC target scope. Citation Format: Raffaella Rossin, Martijn H. den Brok, Lieke W. Wouters, Joep Houkes, Ron M. Versteegen, Marleen H. van Stevendaal, Luc H. Zijlmans, Maria Cincotta, Jay M. Feingold, laurens H. Kleijn, Marc S. Robillard. Preclinical development of TGW101, a first in class click-cleavable ADC with MMAE against non-internalizing pan-carcinoma marker TAG72. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1794.