Abstract Purpose: While antibody-drug conjugates (ADCs) are generally assumed to preserve the pharmacokinetic/pharmacodynamic (PK/PD) properties of their payloads, the extent to which conjugation alters their mechanism of action remains underexplored. This study investigated whether ADC conjugation can fundamentally reprogram payload pharmacology and clarified the downstream consequences for antitumor efficacy and immune activation beyond conventional delivery advantages. Experimental Design: Using MORAb-202, an ADC consisting of the clinically approved eribulin linked to a folate receptor alpha (FRα)-targeting antibody, we performed intratumoral pharmacokinetic/pharmacodynamic (PK/PD) and pharmacometabolomic analyses in xenograft models with varying FRα expression. Intratumoral concentrations of released eribulin and phospholipid profiles were quantified by liquid chromatography-mass spectrometry. We compared effects of MORAb-202 and free eribulin on ferroptosis, immunogenic cell death (ICD), and tumor immune infiltration. Therapeutic efficacy was tested as monotherapy and in combination with pembrolizumab in a human peripheral blood mononuclear cells co-implantation model. Results: ADC-conjugated eribulin achieved 20-fold higher intratumoral retention of eribulin compared to the free eribulin in AUC value. Metabolomics analysis revealed that MORAb-202 robustly induced ferroptosis, characterized by ACSL4 upregulation, GPX4 depletion, lipid peroxidation, and arachidonic acid remodeling. Unlike free eribulin, MORAb-202 triggered ICD, evidenced by HMGB1 expression and enhanced recruitment of total/activated/PD-1+ T cells and dendritic cells. Furthermore, ferroptosis responses induced by free eribulin were reversible, whereas ADC-conjugated eribulin induced irreversible and sustained responses. The combination of MORAb-202 with pembrolizumab enhanced tumor control beyond either monotherapy. Conclusions: ADC conjugation reprograms payload’s pharmacodynamics, inducing ferroptosis and ICD unattainable with free payload, even at clinically equivalent doses. This highlights a pharmacodynamic threshold unique to the ADC formulation. These findings stress the need for intratumoral PK/PD evaluation and identify ferroptosis-linked lipid remodeling as a novel ADC mechanism, supporting rational combination with immunotherapy in precision oncology. Citation Format: Shigehiro Koganemaru, Hirobumi Fuchigami, Hiroshi Tsugawa, Hiroko Shinohara, Yasutoshi Kuboki, Toshimitsu Uenaka, Toshihiko Doi, Masahiro Yasunaga. ACSL4 mediated ferroptosis and its potential role in enhancing the efficacy of antibody-drug conjugates abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1816.
Koganemaru et al. (Fri,) studied this question.