Abstract 397: Combinatorial use of VHL and KEAP1-based PROTACs reveals unexpected synergy and hook effect relief

Abstract Proteolysis-targeting chimeras (PROTACs) are bifunctional molecules bridging a target protein with an E3 ubiquitin ligase, promoting its ubiquitylation and degradation. Unlike traditional inhibitors, PROTACs exploit transient interactions, enabling the selective degradation of “undruggable” proteins, thereby expanding the landscape of druggable targets. However, PROTACs are not without limitations. The “hook effect”—a phenomenon where high PROTAC concentrations reduce efficacy due to inactive binary complex formation—compromises their clinical utility. Additionally, single PROTACs may fail to achieve complete degradation due to insufficient polyubiquitination or suboptimal E3 ligase recruitment, limiting their therapeutic efficacy. These challenges highlight the need for strategies to enhance PROTAC performance and so therapeutic applicability. In this study, we introduce a novel dual-PROTAC strategy that recruits two distinct E3 ligases, such as KEAP1 and VHL, to cooperatively degrade KRAS(G12D) and Androgen Receptor (AR). Our data demonstrate that combining KEAP1- and VHL-recruiting PROTACs synergistically enhances target degradation, reduces the required dosing, and minimizes off-target effects. Notably, KEAP1 recruitment offers the unique advantage to favour polyubiquitin chains elongation, thereby improving proteasomal recognition. In conclusion, dual-targeting approach represents a promising avenue for optimizing PROTAC-based therapeutics. Citation Format: Sehbanul Islam, Haihong Jin, Dong Liu, Dan Lu, Yunkai Zhang, Renxu Chang, Joel Austin, Thomas Beer, Hsin-Yao Tang, Lan Huang, James Tonra, Luca Busino. Combinatorial use of VHL and KEAP1-based PROTACs reveals unexpected synergy and hook effect relief [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 397.