Bortezomib as a therapeutic candidate for neuroblastoma.

Outcomes remain poor in neuroblastoma despite intensive treatment. Agents with potential efficacy can be drawn from anti-neoplastic drugs introduced for other malignancies. Bortezomib, a proteasome inhibitor, modulates cell-signaling molecules leading to apoptosis. Bortezomib, alone and in combination with other agents, was tested across an in vitro panel of neuroblastic, stromal, and chemo-resistant neuroblastoma cell types to determine its effect on cell viability and to assess for interactions between bortezomib and other chemotherapeutic agents that either limit or increase overall response. Each subtype of neuroblastoma was sensitive to bortezomib and killing occurred with EC50 values of approximately 50 nM. When bortezomib was combined with other agents (doxorubicin, etoposide, SN-38, carboplatin, or cisplatin), no antagonism was observed. The bortezomib-doxorubicin combination was especially effective, demonstrating synergy on isobolographic analysis and resulting in a decrease in EC50 from 50 ng/mL with doxorubicin alone to 5 ng/mL with 25 nM bortezomib. Interestingly, the different cell types exhibited varying response patterns to treatment with bortezomib alone and in combination with other drugs suggesting different mechanisms may be engaged. A decision analysis, incorporating these results showing efficacy in all cell types, the synergy obtained in combination, and the available toxicity data, supports a phase II clinical trial of bortezomib in neuroblastoma.