Preclinical characterization of TRO-01, a novel CLDN18.2-targeting ADC, with potent anti-tumor efficacy and favorable PK and safety

Claudin 18.2 (CLDN18.2) is a tight junction protein normally restricted to the gastric mucosa. Loss of epithelial polarity during malignant transformation exposes CLDN18.2 on the surface of gastric and gastroesophageal junction (G/GEJ) adenocarcinoma cells. As CLDN18.2 is highly expressed in 30-40% of G/GEJ cancers and is associated with poor prognosis, it has emerged as a promising therapeutic target for gastric cancer, where effective targeted therapies remain limited. We developed TRO-01, an antibody-drug conjugate (ADC) composed of a fully human anti-CLDN18.2 monoclonal antibody conjugated to a topoisomerase I inhibitor via the proprietary TROSIG TM linker. This cleavable, highly stable, and hydrophilic linker enables a high and uniform drug-to-antibody ratio (DAR) of 8. In vitro studies demonstrated that TRO-01 specifically binds to CLDN18.2 but not to CLDN18.1, exhibiting enhanced affinity compared with competitor antibodies, with cell binding affinities in the single nanomolar range across tested cell lines. Additionally, TRO-01 showed efficient internalization and potent cytotoxicity in CLDN18.2-positive cell lines, with IC 50 values ranging from sub-nanomolar to double-digit nanomolar depending on the cell type. In vivo, TRO-01 treatment resulted in significant tumor growth inhibition (TGI) in both cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) models. In the Patu8988s CDX model, a single dose of 3 or 6 mg/kg resulted in 86% and 101% TGI, respectively. In the SNU-601 CDX model, BIW x 4 dosing at 0.3 or 0.5 mg/kg resulted in 109% and 111% TGI. In two gastric and two pancreatic PDX models, TRO-01 treatment (QW x 2, 2.7 mg/kg) resulted in 89% and 93% TGI in gastric, and 75% and 84% TGI in pancreatic PDXs, with no significant body weight loss. Pharmacokinetic studies in monkeys demonstrated favorable PK properties (t 1/2 = 7.2 days, AUC = 13,800 hr·μg/mL, CL = 0.364 mL/hr/kg, Vd = 0.082 L/kg at 5 mg/kg). Toxicology studies in cynomolgus monkeys revealed a favorable safety profile, with a highest non-severely toxic dose (HNSTD) of 40 mg/kg after single dosing. Collectively, these findings highlight TRO-01 as a promising therapeutic candidate for the treatment of CLDN18.2-expressing gastrointestinal cancers.