PURPOSE

Inhibition of the proteasome leads to the activation of survival pathways in addition to those that promote cell death. We hypothesized that down-regulation of interleukin-6 (IL-6) signaling using the monoclonal antibody CNTO 328 would enhance the antitumor activity of the proteasome inhibitor bortezomib in multiple myeloma by attenuating inducible chemoresistance.

EXPERIMENTAL DESIGN

The cytotoxicity of bortezomib, CNTO 328, and the combination, along with the associated molecular changes, was assessed in IL-6-dependent and IL-6-independent multiple myeloma cell lines, both in suspension and in the presence of bone marrow stromal cells and in patient-derived myeloma samples.

RESULTS

Treatment of IL-6-dependent and IL-6-independent multiple myeloma cell lines with CNTO 328 enhanced the cytotoxicity of bortezomib in a sequence-dependent fashion. This effect was additive to synergistic and was preserved in the presence of bone marrow stromal cells and in CD138(+) myeloma samples derived from patients with relative clinical resistance to bortezomib. CNTO 328 potentiated bortezomib-mediated activation of caspase-8 and caspase-9 and the common downstream effector caspase-3; attenuated bortezomib-mediated induction of antiapoptotic heat shock protein-70, which correlated with down-regulation of phosphorylated signal transducer and activator of transcription-1; and inhibited bortezomib-mediated accumulation of myeloid cell leukemia-1, an effect that was associated with down-regulation of phosphorylated signal transducer and activator of transcription-3.

CONCLUSIONS

Taken together, our results provide a strong preclinical rationale for the clinical development of the bortezomib/CNTO 328 combination for patients with myeloma.