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

Background: 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. Methods: We conducted a pilot trial to evaluate the activity of single-agent bortezomib in CML. Seven patients with imatinibrefractory CML were treated with bortezomib at a dose of 1.5 mg/m² on days 1, 4, 8, and 11 every 3 weeks. Results: 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. Conclusion: 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.