Leukemia https://doi.org/10.1038/s41375-018-0216-8 ARTICLE Multiple myeloma gammopathies Spectrum and functional validation of PSMB5 mutations in multiple myeloma Santiago Barrio 1 ● Thorsten Stühmer 1 ● Matteo Da-Viá 1 ● Clara Barrio-Garcia 2 ● Nicola Lehners 3 ● Andrej Besse 4 ● Isabel Cuenca 5 ● Andoni Garitano-Trojaola 1 ● Severin Fink 1 ● Ellen Leich 6 ● Manik Chatterjee 1 ● Christoph Driessen 4 ● Joaquin Martinez-Lopez 5 ● Andreas Rosenwald 6,7 ● Roland Beckmann 2 ● Ralf C. Bargou 1 ● Esteban Braggio 8 ● A. Keith Stewart 8,9 ● Marc S. Raab 3 ● Hermann Einsele 1 ● K. Martin Kortüm 1 Received: 8 May 2018 / Revised: 22 May 2018 / Accepted: 30 May 2018 © Springer Nature Limited 2018 Abstract 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. Introduction Multiple myeloma (MM) is a malignant plasma cell dis- ease that is characterized by profound genetic hetero- geneity [1–4]. An increasing number of anti-MM compounds have substantially improved patient survival over the past decade [5]. Nevertheless, even the most intense treatment strategies are unable to prevent disease relapse, acquisition of drug resistance is commonly observed, and long-term disease control is only achieved in a minority of patients. Underlying resistance mechan- isms are poorly understood. We recently were first to report cereblon (CRBN) mutations in highly pretreated MM patients as a cause of resistance against immuno- modulating drugs (IMiDs) [6]. According to the “Big Bang” model of cancer evolution, resistance-mediating alterations are already present in early disease, and it is the selective pressure of antitumor therapy that promotes These authors contributed equally: Santiago Barrio, Thorsten Stühmer. * K. Martin Kortüm kortuem_m@ukw.de 1 Department of Hematology-Oncology, Internal Medicine II, University Hospital Würzburg, Würzburg, Germany 2 Gene Center, Ludwig-Maximilians University, Munich, Germany 3 Department of Internal Medicine V, Heidelberg University Hospital, Heidelberg, Germany 4 Departement of Hematology, Kantonsspital St Gallen, St Gallen, Switzerland 5 Department of Hematology, Hospital Universitario 12 de Octubre, CNIO, Complutense University, Madrid, Spain 6 Institute of Pathology, University of Würzburg, Würzburg, Germany 7 Comprehensive Cancer Center Mainfranken, Würzburg, Germany 8 Division of Hematology-Oncology, Mayo Clinic, Scottsdale, AZ, USA 9 Center for Individualized Medicine, Mayo Clinic, Rochester, MN, USA Electronic supplementary material The online version of this article (https://doi.org/10.1038/s41375-018-0216-8) contains supplementary material, which is available to authorized users. 1234567890();,: 1234567890();,: