Overcoming bortezomib resistance in human B cells by anti-CD20 / rituximab-mediated complement-dependent cytotoxicity and epoxyketone-based irreversible proteasome inhibitors

Sue Ellen Verbrugge, Marjon Al, Yehuda G Assaraf, Denise Niewerth, Johan Van Meerloo, Jacqueline Cloos, Michael Van Der Veer, George L Scheffer, Godefridus J Peters, Elena T Chan, Janet L Anderl, Christopher J Kirk, Sonja Zweegman, Ben A C Dijkmans, Willem F Lems, Rik J Scheper, Tanja D De Gruijl, Gerrit Jansen

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

UNLABELLED: BACKGROUND: In clinical and experimental settings, antibody-based anti-CD20/rituximab and small molecule proteasome inhibitor (PI) bortezomib (BTZ) treatment proved effective modalities for B cell depletion in lymphoproliferative disorders as well as autoimmune diseases. However, the chronic nature of these diseases requires either prolonged or re-treatment, often with acquired resistance as a consequence. METHODS: Here we studied the molecular basis of acquired resistance to BTZ in JY human B lymphoblastic cells following prolonged exposure to this drug and examined possibilities to overcome resistance by next generation PIs and anti-CD20/rituximab-mediated complement-dependent cytotoxicity (CDC). RESULTS: Characterization of BTZ-resistant JY/BTZ cells compared to parental JY/WT cells revealed the following features: (a) 10-12 fold resistance to BTZ associated with the acquisition of a mutation in the PSMB5 gene (encoding the constitutive $β$5 proteasome subunit) introducing an amino acid substitution (Met45Ile) in the BTZ-binding pocket, (b) a significant 2-4 fold increase in the mRNA and protein levels of the constitutive $β$5 proteasome subunit along with unaltered immunoproteasome expression, (c) full sensitivity to the irreversible epoxyketone-based PIs carfilzomib and (to a lesser extent) the immunoproteasome inhibitor ONX 0914. Finally, in association with impaired ubiquitination and attenuated breakdown of CD20, JY/BTZ cells harbored a net 3-fold increase in CD20 cell surface expression, which was functionally implicated in conferring a significantly increased anti-CD20/rituximab-mediated CDC. CONCLUSIONS: These results demonstrate that acquired resistance to BTZ in B cells can be overcome by next generation PIs and by anti-CD20/rituximab-induced CDC, thereby paving the way for salvage therapy in BTZ-resistant disease.
Original languageEnglish
Pages (from-to)2-12
Number of pages11
JournalExperimental hematology & oncology
Volume2
Issue number1
DOIs
Publication statusPublished - 2013

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