Phase I Dose Escalating Trial of Bortezomib (Velcade®) in Combination with Idarubicin and Cytarabine in Patients with Acute Myeloid Leukemia.

Conventional therapy for acute myeloid leukemia (AML) consists of a combination of cytarabine and an anthracycline such as idarubicin. Currently, most patients ultimately fail treatment due to leukemia cell resistance to drug therapy. In vitro experiments have shown that the addition of a proteasome inhibitor to an anthracycline results in synergistic cytotoxicity to leukemia cells. Hence, we initiated this phase I trial in patients to see if bortezomib could be safely added to conventional treatment. Patients over age 60 with AML or any patient 18 or older with relapsed disease after a remission of at least 3 months (not refractory) were eligible. All patients received idarubicin 12 mg/m² on days 1–3 and cytarabine 100 mg/m² by continuous infusion days 1–7. In addition, patients received bortezomib by IV bolus on days 1, 4, 8, and 11. Cohorts of 3 to 6 patients were entered using increasing doses of bortezomib in order to determine the maximum tolerated dose (MTD). The first cohort received 0.7 mg/m² of bortezomib with each bolus. If dose limiting toxicity (DLT) was encountered, then cohort advancement was restricted. DLTs included prolonged myelosuppression, neuropathy, and other grade 3 or 4 toxicities. Dose escalation would proceed to 1.0 mg/m² and then to 1.3 mg/m² if tolerated. No escalation was planned beyond 1.3 mg/m². To date 14 patients have been entered on this study. In the first cohort of 3 patients with bortezomib at 0.7 mg/m², a DLT due to prolonged neutropenia was encountered, so an additional 3 patients were entered at this dose level. No DLTs were encountered among these additional patients, so 3 more patients were entered with bortezomib at 1.0 mg/m². One of these patients experienced prolonged thrombocytopenia and thus 3 additional patients were enrolled at 1.0 mg/m². No DLTs were encountered among these additional patients, and thus the next cohort of patients with bortezomib at 1.3 mg/m² was opened. To date, two patients have been enrolled at this dose level. The plan is to enroll a third patient at this level and to assess for possible DLTs. Among the 12 patients evaluable for response, there have been 4 patients achieving complete remission, 3 patients achieving remission without complete recovery of platelet count (CRp defined as having met criteria for CR but with 25,000–99,000 platelets/μl), 2 patients achieving a partial remission (CR but with 5–24% bone marrow blasts), and 3 patients failing to respond. In conclusion, bortezomib at 0.7 mg/m² and 1.0 mg/m² in the day 1, 4, 8, and 11 schedule can be added to idarubicin and cytarabine with acceptable toxicity. This study continues in an attempt to determine whether bortezomib can be escalated safely to 1.3 mg/m² in this combination. Additional patients will be enrolled at the candidate MTD to gain confidence in the safety and activity at this level. Correlative science studies are planned.