A Phase 1 Study of Lenalidomide in Combination with Mitoxantrone, Etoposide, and Ara-C in Patients with Relapsed or Refractory Acute Myeloid Leukemia

Background: The prognosis for patients with relapsed acute myeloid leukemia (AML) remains extremely poor. Standard reinduction regimens, such as mitoxantrone, etoposide, and ara-C (MEC), have been associated with complete remission rates in the 23 to 30% range. Lenalidomide (Len), an immunomodulatory drug, has efficacy in relapsed AML and has been shown to augment the effects of standard chemotherapies (anthracyclines and ara-C) in preclinical AML studies. These data prompted the current phase 1 study of Len in combination with MEC in pts with relapsed AML.

Methods: The trial included pts (≥ 18 yrs) with relapsed or refractory AML. The primary objective was determination of the maximum tolerated dose (MTD) of Len when given in combination with MEC. Secondary objectives included safety, efficacy and time to count recovery. The study examined escalating doses (5-10 mg) of Len given daily for the first 14 days in combination with standard MEC doses of mitoxantrone (8 mg/m²/d), etoposide (100 mg/m²/d), and ara-C (1000 mg/m²/d) on days 4 through 8. Due to observations of prolonged count recovery, the Len dosing schedule was amended by reducing the duration of treatment to 10 days starting on Day 1. The dose of len was then re-escalated starting at 5 mg/d (5-10-25-50). A standard 3+3 dose-escalation design was used. Dose limiting toxicity was defined as Grade IV rash or Grade IV neuropathy during the first 28 day period, or delayed neutrophil (ANC <500/mL) or platelet (platelet count <20,000/mL) recovery beyond Day 45 after start of re-induction chemotherapy in the absence of persistent AML. Pts achieving a complete remission (CR) or complete remission with incomplete blood count recovery (CRi) went on to consolidation chemotherapy or hematopoietic stem cell transplantation at the discretion of the treating physician.

Results: A total of 33 pts have been enrolled in the study (25 escalation phase [5 mg days 1-14, n=3; 10 mg days 1-14, n=6; 5 mg days 1-10, n=3; 10 mg days 1-10, n=3; 25 mg days 1-10, n=3; 50 mg days 1-10, n=6] and 8 expansion phase pts at 50 mg/d days 1-10). One patient was enrolled, found to be ineligible, and not treated. The median age was 62 years (range, 28-74), 45% were male and the median number of prior treatments was 2. Three dose limiting toxicities, all due to delayed count recovery past day 45, were observed in the escalation phase (n = 2/6 pts in the 10 mg/d day1-14 dose group and n = 1/6 in the in the 50 mg/d day1-10 dose group). The RP2D of Len in combination with MEC was 50 mg/d on days 1-10. Among the 14 pts treated at the RP2D, common grade 3/4 adverse events (AEs) regardless of causality were mainly hematologic including febrile neutropenia (36%). Overall 4 pts including none treated at the RP2D died during treatment. All of the on-treatment deaths, (grade 5 sepsis, n =1; infection, n=1; respiratory failure, n =2), were determined to be unrelated to the study drug. 32 pts were evaluable for response (one pt too early for assessment) with 12 pts achieving a CR and 1 pt a CRi with a total CR/CRi rate of 41% (95% CI: 24-59%). The median time to a neutrophil count of 1500/mL was 30 days and to a platelet count of 100,000/mL was 22 days.

Conclusions: Len in combination with MEC re-induction chemotherapy for pts with relapsed or refractory AML was generally well tolerated and associated with an improved response rate as compared to historical controls. The safety profile was consistent with reported events in other MEC chemotherapy trials. Overall, these data suggest further exploration of high-dose Len in combination with MEC.