Abstract Background: Overexpression of NAD(P)H:quinone oxidoreductase 1 (NQO1) has been linked to poor prognosis and therapy resistance in solid tumors, but its role in multiple myeloma (MM) remains unclear. Combination therapies including proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs), and/or immunotherapies have improved outcomes in MM, yet most patients eventually develop resistant and relapse. We recently identified NQO1 overexpression across PI-resistant MM models and that high NQO1 expression is associated with inferior outcome in PI treated MM patients. Hence, we here extend these findings in an independent MM cohort (n = 93) from our institution and in NQO1 upregulated MM cell line models to examine how NQO1 affects MM immunotherapy targets and sensitivity to standard treatment regimens. Methods: RNA-seq was performed on bone marrow-derived CD138+ cells from 24 newly diagnosed MM (NDMM) and 69 relapsed/refractory MM (RRMM) patients, as well as MM cell lines. Surface density of immunotherapy targets was quantified via direct stochastic Optical Reconstruction Microscopy (dSTORM). Sensitivity to PIs and IMiDs was assessed using AlamarBlue assays. Results: In the MM RNA-seq cohort, NQO1 expression was significantly higher in RRMM compared with NDMM (p = 0.0002), supporting an association of NQO1 with treatment-exposed, advanced disease. Furthermore, overexpression of NQO1 in MM cell lines led to an increased IC50 for bortezomib and carfilzomib, whereas IMiDs sensitivity remained intact. No upregulation of PI resistance-related genes was identified by RNA-seq. To test whether NQO1-dependent mechanisms are causative for PI resistance, NQO1-high MM cells were treated with NQO1 inhibitor ES936, which restored the sensitivity to both PIs to the wild type levels. In subsequent dSTORM analysis, no differences were observed in BCMA, SLAMF7, or GPRC5D, whereas CD38 surface density was significantly reduced in both NQO1-High myeloma cell lines. Consistent with the expression data, NQO1-overexpressing cells showed reduced sensitivity to CD38-directed therapies (daratumumab (Dara) and isatuximab (Isa). Notably, NQO1 inhibition with ES936 restored CD38 surface expression and rescued Dara and Isa responses, supporting that NQO1 is directly involved in CD38 downregulation and resistance to anti-CD38 antibodies. Of note, RNA-seq comparison of NQO1-high vs. WT MM models did not reveal changes in CD38 mRNA levels, pointing toward a post-translational mechanism, such as altered protein stability or trafficking. Conclusions: NQO1 is upregulated in RRMM and functionally induces resistance to PIs and CD38-directed therapies which are widely used in current MM treatment. Inhibition of NQO1 with ES936 rescues CD38 expression, and restores PI sensitivity and anti-CD38 responses, supporting NQO1 as a promising target in treatment-exposed or relapsed MM. Citation Format: Seungbin Han, Christina Verbruggen, Lenka Besse, Shilpa Kurian, Silvia Nerreter, Umair Munawar, Marietta Truger, Elena Gerhard-Hartmann, Andrej Besse, Ann-Sophie Hainold, Cornelia Vogt, Emma Besant, Nina Rein, Max Köppel, Xiang Zhou, Claudia Haferlach, Andreas Rosenwald, Christoph Driessen, Ondrej Slaby, Hermann Einsele, Leo Rasche, Markus Sauer, Johannes Waldschmidt, K. Martin Kortüm. NQO1 as a target to overcome therapy resistance in multiple myeloma 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 3912.
Han et al. (Fri,) studied this question.