• CRBN interacts with the DNA damage-binding protein-1 (DDB1), Cullin 4 (Cul4A or Cul4B), and regulator of Cullins1 (RoC1) to form the functional E3 ubiquitin ligase complex. In this complex, CRBN functions as a substrate receptor of E3 ubiquitin ligase complex and targets proteins for proteolysis through a ubiquitin-proteasome pathway.
• The CDS of human CRBN gene that encodes the full-length protein was inserted into the mouse Crbn exons 2-3. The B-NDG hCRBN mice will express the human CRBN protein, while mouse Crbn will no longer be expressed.
• CRBN protein was detected in the lung, liver, kidney, spleen and heart of wild-type B-NDG and homozygous B-NDG hCRBN mice, as the antibody was cross-recognize both human and mouse CRBN.
• Mouse Crbn mRNA was detectable in spleen of wild-type mice (+/+). Human CRBN mRNA was detectable in B-NDG hCRBN mice (H/H) but not in wild-type mice.
• Tumor cell lines inoculated in B-NDG hCRBN mice can be used to study the in vivo efficacy of CRBN small molecule drugs, molecular glue drugs based on CRBN, or PROTAC drugs based on CRBN.

Gene targeting strategy for B-NDG hCRBN mice . The CDS of human CRBN gene that encodes the full-length protein was inserted into the mouse Crbn exons 2-3. The B-NDG hCRBN mice will express the human CRBN protein, while mouse Crbn will no longer be expressed.

Western blot analysis of CRBN protein expression in homozygous B-NDG hCRBN mice. Various tissue lysates were collected from wild-type B-NDG (+/+) mice and homozygous B-NDG hCRBN mice (H/H), and then analyzed by western blot with anti-CRBN antibody. 40 μg total proteins were loaded for western blotting analysis. CRBN protein was detected in the lung, liver, kidney, spleen and heart of wild-type B-NDG and homozygous B-NDG hCRBN mice, as the antibody is cross-recognize both human and mouse CRBN. (There is no β-actin in the heart tissue)

Strain specific analysis of CRBN mRNA expression in wild-type B-NDG mice and homozygous B-NDG hCRBN mice by RT-PCR. Spleen RNA was isolated from wild-type B-NDG mice (+/+) and homozygous B-NDG hCRBN mice (H/H), then cDNA libraries were synthesized by reverse transcription, followed by PCR with mouse or human CRBN primers. Mouse Crbn mRNA was detectable in wild-type B-NDG mice. Human CRBN mRNA was detectable only in homozygous B-NDG hCRBN mice but not in wild-type mice.

Antitumor activity of dBET6 PROTAC (QCA-570) in B-NDG hCRBN mice.(A) dBET6 PROTAC inhibited MV-4-11 cells tumor growth in B-NDG hCRBN mice. Human myelomonocytic leukemia cell line MV-4-11 cells were subcutaneously implanted into homozygous B-NDG hCRBN mice (female, 8-week-old, n=6). Mice were grouped when tumor volume reached approximately 100-150 mm³, at which time they were intraperitoneally injected with dBET6 PROTAC indicated in panel. (B) Body weight changes during treatment. As shown in panel A, In the MV4;11 xenograft model, QCA-570 achieved tumor regression at 1 and 2.5 mg/kg, demonstrating that B-NDG hCRBN mice provide a powerful preclinical model for in vivo efficacy and safe evaluation of dBET6 PROTAC.

Note: The efficacy of the PROTAC can be observed in both wild-type NDG mice and B-NDG hCRBN mice. After administration, the B-NDG hCRBN mice exhibited significant weight loss, lethargy, and even mortality. Additionally, tumor rebound in B-NDG hCRBN mice was slower, indicating broader drug distribution in the humanized mice and better reflection of drug toxicity.