Despite an increasing number of approved therapies, multiple myeloma (MM) remains an incurable disease and only a small number of patients achieve prolonged disease control. Some genes have been linked with response to commonly used anti-MM compounds, including immunomodulators (IMiDs) and proteasome inhibitors (PIs). In this manuscript, we demonstrate an increased incidence of acquired proteasomal subunit mutations in relapsed MM compared to newly diagnosed disease, underpinning a potential role of point mutations in the clonal evolution of MM. Furthermore, we are first to present and functionally characterize four somatic PSMB5 mutations from primary MM cells identified in a patient under prolonged proteasome inhibition, with three of them affecting the PI-binding pocket S1. We confirm resistance induction through missense mutations not only to Bortezomib, but also, in variable extent, to the next-generation PIs Carfilzomib and Ixazomib. In addition, a negative impact on the proteasome activity is assessed, providing a potential explanation for later therapy-induced eradication of the affected tumor subclones in this patient.

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Cereblon (CRBN), a target of immunomodulatory drugs (IMiD), forms the CRL4 CRBN E3 ubiquitin ligase (CRL4) complex with DDB1, CUL4B and ROC1. 1,2 Under the influence of IMiD, CRL4 polyubiquitinates and thus depletes the transcription factors IKZF1 and IKZF3, resulting in cytotoxicity to multiple myeloma (MM) cells. In vitro, CRBN and IKZF1/3 mutations affecting the CRBN-lenalidomide binding site (degron) cause drug resistance to IMiD. [3][4][5] We hypothesized that mutations in the other components of the CRL4 complex and its targets, Ikaros and Aiolos, likewise interfere with ubiquitin ligase activity, thus contributing to resistance to IMiD. In order to select the most promising patient-derived candidate mutations for functional validation, we first generated a comprehensive overview of point mutations

Multiple myeloma is a heterogeneous disease whose pathogenesis has not been completely elucidated. Although B-cell receptors play a crucial role in myeloma pathogenesis, the impact of clonal immunoglobulin heavy-chain features in the outcome has not been extensively explored. Here we present the characterization of complete heavychain gene rearrangements in 413 myeloma patients treated in Spanish trials, including 113 patients characterized by next-generation sequencing. Compared to the normal B-cell repertoire, gene selection was biased in myeloma, with significant overrepresentation of IGHV3, IGHD2 and IGHD3, as well as IGHJ4 gene groups. Hypermutation was high in our patients (median: 8.8%). Interestingly, regarding patients who are not candidates for transplantation, a high hypermutation rate (≥7%) and the use of IGHD2 and IGHD3 groups were associated with improved prognostic features and longer survival rates in the univariate analyses. Multivariate analysis revealed prolonged progression-free survival rates for patients using IGHD2/IGHD3 groups (HR: 0.552, 95% CI: 0.361−0.845, p = 0.006), as well as prolonged overall survival rates for patients with hypermutation ≥7% (HR: 0.291, 95% CI: 0.137−0.618, p = 0.001). Our results provide new insights into the molecular characterization of multiple myeloma, highlighting the need to evaluate some of these clonal rearrangement characteristics as new potential prognostic markers.