The proteasome inhibitor carfilzomib functions independently of p53 to induce cytotoxicity and an atypical NF-?B response in chronic lymphocytic leukemia cells.

ABSTRACT: The proteasome consists of chymotrypsin-like (CT-L), trypsin-like, and caspase-like subunits that cleave substrates preferentially by amino acid sequence. Proteasomes mediate degradation of regulatory proteins of the p53, Bcl-2, and nuclear factor-?B (NF-?B) families that are aberrantly active in chronic lymphocytic leukemia (CLL). CLL remains an incurable disease, and new treatments are especially needed in the relapsed/refractory setting. We therefore investigated the effects of the proteasome inhibitor carfilzomib (CFZ) in CLL cells.Tumor cells from CLL patients were assayed in vitro using immunoblotting, real-time polymerase chain reaction, and electrophoretic mobility shift assays. In addition, a p53 dominant-negative construct was generated in a human B-cell line.Unlike bortezomib, CFZ potently induces apoptosis in CLL patient cells in the presence of human serum. CLL cells have significantly lower basal CT-L activity compared to normal B and T cells, although activity is inhibited similarly in T cells versus CLL. Co-culture of CLL cells on stroma protected from CFZ-mediated cytotoxicity; however, PI3K inhibition significantly diminished this stromal protection. CFZ-mediated cytotoxicity in leukemic B cells is caspase-dependent and occurs irrespective of p53 status. In CLL cells, CFZ promotes atypical activation of NF-?B evidenced by loss of cytoplasmic I?B?, phosphorylation of I?B?, and increased p50/p65 DNA binding, without subsequent increases in canonical NF-?B target gene transcription.Together, these data provide new mechanistic insights into the activity of CFZ in CLL and support phase I investigation of CFZ in this disease.

SUBMITTER: Gupta SV 

PROVIDER: S-EPMC3644010 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature