Experimental Hematology & Oncology (Jan 2013)

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

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

DOI
https://doi.org/10.1186/2162-3619-2-2
Journal volume & issue
Vol. 2, no. 1
p. 2

Abstract

Read online

Abstract 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 β5 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 β5 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.

Keywords