Abstract 7011: Humanized CRBN knockin mice enable in vivo assessment the efficacy and toxicity of CRBN-targeted protein degraders

Abstract Protein degraders have emerged as a transformative therapeutic approach in the past decade, enabling targeted degradation of proteins, including traditionally undruggable targets, by facilitating the recruitment of E3 ubiquitin ligases. Among these, molecular glues such as thalidomide and its derivatives, and PROteolysis TArgeting Chimeras (PROTACs), have gained significant attention. Cereblon (CRBN), a key component of the Cullin 4 RING E3 ubiquitin ligase (CRL4), is the most extensively studied target in protein degrader research. CRBN interacts with DDB1, Cullin 4 (CUL4A/B), and RBX1 to form the CRL4^CRBN complex, which mediates substrate recognition and degradation. Thalidomide derivatives bind to CRBN, modulating substrate specificity and promoting substrate degradation. However, differences at the V388 and E377 residues between human and mouse CRBN proteins (94% homology) impede the antitumor efficacy and teratogenicity of thalidomide in mice, limiting suitable preclinical models. To address this, we developed a humanized CRBN knockin mouse model by inserting the human CRBN coding region (exon 2-11) and a WPRE/polyA cassette into the mouse Crbn locus using ES cell-based gene targeting. This model expresses full-length human CRBN in targeted cells. We validated human CRBN (hCRBN) expression across multiple tissues, including spleen, liver, brain, and intestines, via RT-PCR and western blot. Lenalidomide and CC-885 treatments of hCRBN splenocytes demonstrated the degradation of substrate proteins CK1α and GSPT1. Pharmacokinetic analysis revealed no significant differences between hCRBN knockin and wild-type C57BL/6 mice. In vivo CC-885 treatment induced on-target toxicity, as evidenced by rapid lethality, GSPT1 degradation, and increased pathological scores in hCRBN knockin mice. Our humanized CRBN mouse model serves as a robust preclinical platform for evaluating the efficacy and toxicity of CRBN-targeted protein degraders, offering valuable insights for drug development. Citation Format: Yi Li, Xiaolei Qiu, Liping Feng, Dongxiao Feng, Ruilin Sun. Humanized CRBN knockin mice enable in vivo assessment the efficacy and toxicity of CRBN-targeted protein degraders [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 7011.