Abstract 1792: Comprehensive identification of factors involved in the resistance mechanism of a novel cereblon modulator in multiple myeloma cells

Abstract Background: Multiple myeloma (MM) is a hematologic malignancy characterized by clonal proliferation of plasma cells. Although novel agents such as antibody-based drugs and T cell engagers have improved outcomes, MM remains incurable and relapse is inevitable. Immunomodulatory drugs (IMiDs), including lenalidomide and pomalidomide, are central to MM therapy, but resistance frequently develops with long-term use. Cereblon modulators (CELMoDs), a new generation of IMiDs, are expected to overcome such resistance mechanisms. Mezigdomide, a novel CELMoD, demonstrated an overall response rate of approximately 40% in patients with relapsed/refractory MM (Richardson et al., N Engl J Med, 2023). However, early relapse after an initial response remains a clinical concern. Methods: To elucidate the mechanisms of mezigdomide resistance, we utilized MM cell lines with differential sensitivity to the drug. Expression levels of cereblon (CRBN), IKZF1, and IKZF3—key mediators of IMiD and CELMoD activity—were analyzed by Western blotting. RNA sequencing was then performed to identify gene expression changes associated with resistance. Candidate resistance genes were further validated by RT-PCR, and comparative analyses were conducted with lenalidomide- and pomalidomide-treated cells. Results: CRBN, IKZF1, and IKZF3 expression levels did not differ between mezigdomide-sensitive and -resistant cells. RNA sequencing revealed several differentially expressed genes potentially associated with resistance. Validation studies confirmed distinct gene expression patterns between resistant and sensitive cell lines. Conclusions: This study provides the first insights into molecular mechanisms underlying mezigdomide resistance in MM. Identification of these candidate resistance factors may contribute to the development of predictive biomarkers and strategies to overcome CELMoD resistance. Citation Format: Sho Osawa, Tomofumi Yamamoto, Rina Tamaru, Natsumi Seki, Maiko Matsushita. Comprehensive identification of factors involved in the resistance mechanism of a novel cereblon modulator in multiple myeloma cells 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 1792.