Preclinical Evaluation of AHT-102, a CLDN18.2 × CD3 Bispecific Antibody: Pharmacokinetics, Anti-Tumor Efficacy, Tissue Distribution, and Safety Profile.

[BACKGROUND AND OBJECTIVES] Claudin18.2 (CLDN18.2) is a promising therapeutic target overexpressed in various tumor tissues. While CD3-engaging bispecific antibodies show great potential, their clinical application is often limited by poor efficacy in solid tumors and significant safety risks, such as cytokine release syndrome (CRS). The objective of this study was to comprehensively evaluate the preclinical anti-tumor efficacy, pharmacokinetics, tissue distribution, and safety profile of AHT-102, a novel Fc-free CLDN18.2 × CD3 bispecific antibody with a low-affinity CD3 arm, to determine its potential for clinical development.

[METHODS] This study evaluated the anti-tumor efficacy of AHT-102 in CLDN18.2-positive gastric cancer mouse models (NUGC4-CLDN18.2). We further assessed its pharmacokinetic characteristics, quantitative tissue distribution using I-labeling, and long-term toxicity in human CD3EDG transgenic mice.

[RESULTS] AHT-102 (0.1, 0.3, and 1 mg/kg) demonstrated significant dose-dependent anti-tumor effects, with tumor weight inhibition reaching 51% at the 1-mg/kg dose. Pharmacokinetic analysis in CD3EDG mice revealed linear characteristics with refined terminal half-lives of 0.762 h, 3.05 h, and 4.25 h for doses of 0.1, 0.5, and 2.5 mg/kg, respectively. Tissue distribution studies confirmed superior targeting specificity; the tumor-to-muscle ratio exceeded 15, and the molecule successfully bypassed the 'T-cell sink' by showing lower accumulation in the lymph nodes compared with the tumor. In vitro, AHT-102 did not induce target-independent cytokine release from peripheral blood mononuclear cells (PBMCs). The maximum tolerated dose (MTD) in human CD3EDG mice reached 13.65 mg/kg, a 136.5-fold margin over the projected clinical starting dose. Observed gastric tissue damage was dose-dependent and reversible upon drug discontinuation.

[CONCLUSIONS] AHT-102, a novel Fab-like bispecific antibody, achieves an optimized therapeutic balance through its low-affinity CD3 arm and Fc-free format. It demonstrates significant anti-tumor efficacy and exceptional targeting specificity while avoiding systemic immunotoxicity typically associated with CD3-targeting agents. These findings provide a robust scientific rationale for the clinical translation of AHT-102 in patients with CLDN18.2-positive cancers.