Deng, Shuhui

Abstract Transcription factors and their cofactors are major and selective nononcogene dependencies in multiple myeloma cells. By performing a gain-of-function perturbation screen in human multiple myeloma cell lines, we identified the inhibitor of DNA binding (ID) genes as putative suppressors of multiple myeloma cell fitness. Among them, ID2 was found to be downregulated in multiple myeloma patient cells and acted as a tumor suppressor by directly binding and repressing the basic helix-loop-helix factor TCF3, also known as E2A. Lower ID2 expression in multiple myeloma cells conferred a proliferative advantage by increasing TCF3 activity, leading to a dependency on this transcription factor. In contrast, ID2 overexpression reduced TCF3 binding to DNA, which resulted in cell-cycle arrest and a halt in multiple myeloma cell proliferation. The myeloma bone marrow milieu supported this process by further decreasing the expression of ID2 and enhancing TCF3 activity, partly via IL6, revealing a mechanism by which the tumor microenvironment affects multiple myeloma cell behavior. Significance: Multiple myeloma cells exploit the oncogenic and proliferative potential of TCF3 by downregulating the transcriptional regulator ID2, a process facilitated by the bone marrow microenvironment.

Background: Deeper depth of response (DpR) after induction therapy, especially gain of negative minimal residual disease (MRD), has been linked to prolonged survival in multiple myeloma (MM). However, flow-MRD examination focuses on the numbers but not on the biological characteristics of residual plasma cells (PCs). Objectives: To explore whether the genetic features of residual tumor cells affect the survival time of patients with MM. Design: A retrospective cohort study. Methods: We investigated the clonality of cytogenetic abnormalities (CAs) of the residual PCs using interphase fluorescence in situ hybridization (iFISH) in the National Longitudinal Cohort of Hematological Diseases in China (NCT04645199). Here, a longitudinal cohort of 269 patients with patient-paired diagnostic and post-induction iFISH results was analyzed. Results: Persistent CAs after induction therapy were detected in about half of the patients (118/269, 43%), and patients with undetectable CAs showed significantly improved survival compared with those with genetically detectable MRD [median progression-free survival (mPFS): 59.7 versus 35.7 months, p < 0.001; median overall survival (mOS): 97.1 versus 68.8 months, p = 0.011]. In addition, different patterns of therapy-induced clonal evolution were observed by comparing the clonal structure of residual PCs with paired baseline samples. Patients who maintained at a high risk during follow-up had the worst survival (mPFS: 30.5 months; mOS: 54.4 months), while those who returned to lower risk or had iFISH− at both time points had the best survival (mPFS: 62.0 months, mOS: not reached). Conclusion: These findings highlighted the prognostic value of genetic testing in residual tumor cells, which may provide a deep understanding of clonal evolution and guide clinical therapeutic strategies.