This study was conducted in accordance with the International Conference on Harmonization and Good Clinical Practice standards. Institutional review board approval was obtained from all participating institutions. All patients provided written informed consent before study participation.
Eligible patients were 18 years or older, with histologically confirmed diagnoses of non-del(5q) MDS, Low or Intermediate-1 IPSS risk group, and Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 or 1. The following World Health Organization (WHO) classification MDS subtypes were included: refractory anemia (RA), refractory nemia with excess blasts type I (RAEB-I), refractory anemia with ring sideroblasts (RARS), refractory cytopenia with multilineage dysplasia (RCMD), refractory cytopenia with multilineage dysplasia with ringed sideroblasts (RCMD-RS), MDS-unclassified (MDS-U), and MDS/myeloproliferative neoplasm-unclassified (MDS/MPN-U) without leukocytosis. Patients were required to have adequate hepatic and renal function. Inclusion criteria allowed multilineage cytopenias with assessment of response by International Working Group (IWG) 2006 criteria , <10% marrow blasts, and ineligibility or unwillingness to undergo allogeneic stem cell transplantation. Patients were excluded for prior allogeneic bone marrow transplantation, a history of IPSS higher-risk MDS or of AML [10, 11], proliferative chronic myelomonocytic leukemia, use of oral corticosteroids at a dose exceeding 10 mg daily, history of hepatitis B/C or human immunodeficiency virus, or an active infection requiring intravenous antibiotics. Patients were not allowed to receive hematopoietic growth factors while on study, and a 4-week washout period for growth factors and all prior MDS treatments was required before study enrollment.
This was a multicenter phase 1 dose-ranging study evaluating ezatiostat in combination with lenalidomide in patients with non-del(5q) IPSS Low or Intermediate-1 risk MDS. The hematologic improvement-erythroid (HI-E), HI-Neutrophil (HI-N), and HI-Platelet (HI-P) rates by IWG 2006 criteria and safety of each treatment group were evaluated to select the optimal dose of ezatiostat in combination with lenalidomide for future studies. Ezatiostat was given at a starting dose of 2000 mg total daily in divided doses (1000 mg PO twice daily) in combination with lenalidomide at a starting dose of 10 mg PO once daily on days 1–21 of a 28-day cycle. In each stage, three to six patients in a standard 3 + 3 design were treated before escalation to the next higher dose level; stage 2 was an ezatiostat/lenalidomide 2500 mg/10 mg dose level. Once dose-escalation was complete, the maximum tolerated dose (MTD) cohort was expanded by an additional 10 patients in stage 2. The primary objectives of this study were to establish the MTD of ezatiostat in combination with lenalidomide as well as to determine the safety of the combination. The secondary objectives of this study were to assess efficacy by determining rates of HI-E, HI-N, and HI-P. Patients were treated until MDS disease progression, lack of MDS response, unacceptable toxicities, or patient withdrawal from the study.
Red blood cell (RBC) transfusion guidelines were provided in the protocol and RBC transfusions were to be given for a hemoglobin (Hgb) level < 9.0 g/dL. All treated patients were monitored for safety and efficacy with physical and laboratory examinations and hematologic response assessments (IWG 2006) were evaluated every two cycles . Adverse events were graded in accordance with the National Cancer Institute − Common Toxicity Criteria for Adverse Events, Version 3.0 (NCI − CTCAE, v3.0; Bethesda, MD) .
Ezatiostat is formulated as 500 mg tablets. Each tablet contains ezatiostat hydrochloride with the following excipients: mannitol, croscarmellose sodium, hypromellose, magnesium stearate, and Opadry Clear. Opradry Clear is a mixture of hypromellose and polyethylene glycol 400.
On day 1 of each treatment cycle, a physical examination and laboratory assessments (complete blood count [CBC] with differential and serum chemistry profile) were obtained, use of concomitant medication(s) was documented, AEs were assessed, and RBC transfusion requirements were documented for the preceding 8-week baseline period. CBC with differential and platelet count was obtained weekly.
Patients who experienced a treatment-related non-hematologic AE grade 3 or higher had treatment delayed for up to 3 weeks or until recovery to grade 1 or baseline, and subsequent treatment resumed at a dose reduced by the amount of ezatiostat of 500 mg (1 tablet) per day. If recovery did not occur after a delay of 21 days, treatment was discontinued and patients were followed until resolution of the AE. Patients were dosed at a starting dose of lenalidomide (Revlimid®) at 10 mg using commercial supply. If a patient experienced prolonged thrombocytopenia and neutropenia, that patient's lenalidomide dosage was adjusted per the lenalidomide package insert. Since lenalidomide is excreted by the kidney, dose adjustments for renal impairment were made in accordance with the package insert.
Assuming the population incidence of an adverse event is 10% or higher, a sample size of 16 patients had a probability of 82% of observing at least one adverse event. All enrolled patients were included in the intent-to-treat (ITT) population. A secondary endpoint of the study was to determine the HI response rate in the erythroid cell line (HI-E) by the IWG MDS criteria (2006) in the ITT and efficacy-evaluable (EE) populations. All enrolled patients who received any amount of ezatiostat in combination with lenalidomide treatment were included in the safety analysis. Patients who received at least two cycles of ezatiostat in combination with lenalidomide treatment and for whom an HI response assessment was completed were included in the EE population. All investigator-determined responses were independently reviewed and confirmed. Efficacy analyses were performed in the ITT and the EE populations by the two dose groups. Exact binomial 95% confidence intervals were provided for response rates. Duration of response was estimated by Kaplan-Meier method. HI-E is defined in the IWG 2006 criteria as RBC-transfusion-dependent patients who experience a clinically significant transfusion reduction by ≥ 4 units from baseline over 8 weeks after the initiation of study treatments (given for Hgb < 9.0 g/dL); RBC transfusion independence is defined as no RBC transfusions required over an 8-week period. Time to HI-E response was calculated from the day of the initiation of study treatment to the end day of the 8-week period when an HI-E was declared. Time to RBC-transfusion independence was calculated from the day of the initiation of study treatment to the end day of an 8-week period free of transfusions. Duration of HI-E response was calculated from the end day of the 8-week period when an HI-E was declared to the first day when an HI-E criterion was no longer met. Duration of RBC-transfusion independence was calculated from the last day after an 8-week period free of transfusions to the date an RBC transfusion was required. These duration-of-response definitions pertained only when transfusion reduction or independence had been sustained beyond 8 weeks, per IWG 2006 criteria.
The safety of ezatiostat in combination with lenalidomide was evaluated by determining the frequency, severity (NCI − CTCAE v3.0), and causal relationship(s) of AEs that occurred during the treatment period and follow-up period of 30 days from the last administration of study drug treatment(s). The incidence and percentage of AEs related to study treatment, as judged by investigators, was reported by total daily dose levels of ezatiostat in combination with lenalidomide.