• Origin: The MC38 cell line is derived from C57BL/6 murine colon adenocarcinoma cells and is a commonly used murine model for colorectal carcinoma.
• Background Information: CRBN (Cereblon) is encoded on human chromosome 3 and functions as a substrate receptor within the CRL4 E3 ubiquitin ligase complex, playing a central role in targeted protein degradation. CRBN is broadly expressed across multiple tissues, including immune cells, hematopoietic tissues, and the central nervous system, and its expression level can influence cellular sensitivity to CRBN-recruiting degraders. As part of the CRL4^CRBN complex, CRBN recruits substrate proteins for ubiquitination and proteasomal degradation. The binding of IMiDs or molecular glues redirects CRBN to degrade neosubstrates such as IKZF1, IKZF3, and GSPT1. Consequently, CRBN is a key target for IMiDs, molecular glues, and PROTACs that induce selective degradation of disease-associated proteins, with CRBN-based degraders currently being developed for cancer, autoimmune, and inflammatory diseases.
• Gene Targeting Strategy: An expression cassette containing an exogenous promoter and the full-length human CRBN sequence was inserted to replace murine exons 2–4. This insertion disrupts the endogenous murine Crbn gene, resulting in a non-functional transcript.
• Tumorigenicity: Confirmed in B-hCRBN mice.
• Application: B-hCRBN MC38 tumor models can be used for the preclinical evaluation of PROTAC drugs targeting human CRBN.

CRBN expression analysis in B-hCRBN MC38 by western blot. B-hCRBN MC38 tumor cells were harvested and assessed with anti-CRBN antibody (CST, 71810). As the antibody was cross-reactive between human and mice, CRBN was detected in the wild-type MC38 cells as well as in both clones of B-hCRBN MC38 cells. As human CRBN was driven by an exogenous promoter, CRBN expression was higher in the B-hCRBN MC38 cells than in wild-type MC38 cells.

Subcutaneous tumor growth of B-hCRBN MC38 cells. B-hCRBN MC38 (1×10⁶) and wild-type MC38 cells (1×10⁶) were subcutaneously implanted into B-hCRBN mice (female, 9-week-old, n=6). Tumor volume and body weight were measured twice a week. (A) Average tumor volume. (B) Body weight. Volume was expressed in mm³ using the formula: V=0.5 × long diameter × short diameter². Results indicate that B-hCRBN MC38 cells were able to establish tumors in vivo and can be used fo refficacy studies. Values are expressed as mean ± SEM.

B-hCRBN MC38 tumor growth curves from individual mouse. B-hCRBN MC38 (1×106) and wild-type MC38 cells (1×106) were subcutaneously implanted into B-hCRBN mice (female, 9-week-old, n=6). Results indicate that B-CRBN MC38 cells were able to establish tumors in vivo and can be used for efficacy studies. Values are expressed as mean ± SEM.

Human CRBN expression evaluated in B-hCRBN MC38 tumor cells by western blot. B-hCRBN MC38 tumor cells were subcutaneously implanted into B-hCRBN mice (female, 9-week-old). At the end of the experiment, tumor tissues were harvested and protein expression was assessed with an anti-CRBN antibody (CST, 71810). Because the antibody is cross-reactive between human and mouse species, CRBN was detected in wild-type MC38 cells as well as in both clones of B-hCRBN MC38 cells. However, because human CRBN expression is driven by an exogenous promoter, overall CRBN levels were higher in B-hCRBN MC38 cells compared to wild-type MC38 cells. These results confirm that B-hCRBN MC38 cells are suitable for in vivo efficacy studies evaluating CRBN-targeting therapies.