Evaluation of carfilzomib to disrupt the apoptotic threshold of B-cell lymphomas by targeting Bcl-2 family members and overcome rituximab (R) chemotherapy resistance.

Abstract

e18514 Background: The addition of R to chemotherapy has improved the clinical outcome of B-cell lymphoma, but also appears to be changing the biology of relapsed disease. We found that repeated exposure of lymphoma cells to R induced deregulation of Bcl-2 family members and the ubiquitin-proteasome system resulting in R and chemotherapy resistance. In an attempt to develop strategies targeting key regulators of the apoptotic pathway, we evaluated the biological effects of carfilzomib, a novel proteasome inhibitor, in lymphoma pre-clinical models. Methods: Experiments were conducted in various rituximab-chemotherapy sensitive (RSCL) and rituximab-chemotherapy resistant (RRCL) or in primary tumor cells isolated from biopsy specimens of patients with B-cell lymphoma [including: diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), and Burkitt's lymphoma (BL)]. RSCL and RRCL were exposed to carfilzomib [LC50 for 48 hours], and changes in Bcl-2 family member levels were evaluated by Western blotting. RSCL, RRCL or tumor cells were exposed to escalating doses of carfilzomib alone or in combination with vorinostat. Changes in mitochondrial potential at 48hrs were quantified via alamar blue reduction and cell viability was determined using the CellTiter-Glo assay. Results: Carfilzomib was active in both RSCL/RRCL and in tumor cells derived from DLBCL, FL and BL. In vitro exposure to carfilzomib resulted in an upregulation of Bak and Noxa levels in RRCL but not in RSCL. Current data demonstrates that in vitro exposure of RSCL or RRCL to carfilzomib enhanced the anti-tumor effects of vorinostat. We are evaluating the effects of carfilzomib in combination with chemotherapy agents. Conclusions: Carfilzomib alters the balance of Bcl-2 members and induces cell death in B-cell lymphoma. In addition, it significantly enhances the anti-tumor activity of vorisnostat. Carfilzomib has the potential of becoming a novel and potent therapeutic strategy in the treatment of rituximab-chemotherapy resistant B-cell lymphomas. No significant financial relationships to disclose.