Pilot study of bortezomib for patients with imatinib-refractory chronic myeloid leukemia in chronic or accelerated phase.

Proteasome inhibitors are anticancer compounds that disrupt the proteolytic activity of the proteasome and lead to tumor cell growth arrest and apoptosis. Bortezomib is a proteasome inhibitor that is currently approved for use in multiple myeloma (MM) and mantle-cell lymphoma. It induces apoptosis of chronic myeloid leukemia (CML) cells in vitro, but the activity of bortezomib in patients with imatinib-resistant CML is unknown. We conducted a pilot trial to evaluate the activity of single-agent bortezomib in CML. Seven patients with imatinib-refractory CML were treated with bortezomib at a dose of 1.5 mg/m2 on days 1, 4, 8, and 11 every 3 weeks. The median number of cycles received was 2. No patient had a hematologic or cytogenetic response. Three patients had a temporary decrease in basophil counts associated with therapy with bortezomib. Six patients experienced grade 3/4 nonhematologic toxicities. Bortezomib had minimal efficacy and considerable toxicity in patients with imatinib-refractory CML. Further studies should focus on alternative approaches to using proteasome inhibitors in the treatment of CML, such as in combination with tyrosine kinase inhibitors (TKIs) or as a strategy to eradicate leukemic stem cells. Copyright © 2011. Published by Elsevier Inc.