A Sequential Two-Stage Dose Escalation Study Evaluating The Safety and Efficacy Of Eltrombopag In Thrombocytopenic Patients With Myelodysplastic Syndrome (MDS) Resistant To Hypomethylating Agents (HMA)

Thrombocytopenia remains a critical management challenge for MDS pts. The outcome of MDS Pts after HMA failure is poor. Eltrombopag is an oral, small non-peptide thormbopoeitin (TPO) receptor agonist. It has biologically distinct effects in part to its binding site on the TPO receptor that is distinct from that for native TPO and other synthetic agonists. We conducted an investigator initiated study with eltrombopag in MDS pts with thrombocytopenia after HMA failure.

The study is a phase 1, dose escalation design. Pts are allocated to dose cohorts of 50, 100, 150, 200, 250 and 300mg/day. Each dose cohort includes 6 pts. Key eligibility criteria include confirmed diagnosis of MDS or acute myeloid leukemia (AML) with 20-30% myeloblasts. Pts must have at least one prior HMA treatment. The mean platelet count within a month of enrollment must be ≤ 50 X 10⁹ /L. Key exclusions include splenic enlargement > 8 cm, bone marrow fibrosis ≥ grade 3, and prior TPO agonist use. The primary objective of the study is to determine the MTD. Dose-limiting toxicity (DLT) is defined as treatment related non-hematological grade 3-4 toxicity. If no DLTs were observed during the first 2 cycles of therapy, the next cohort of patients receives a higher dose of eltrombopag. Pts who did not receive treatment for 8 weeks were replaced for DLT assessment. The secondary endpoints include response, overall survival (OS) and leukemia free survival (LFS).

Thirty-one pts were enrolled. Table-1 summarizes baseline characteristics. Most pts had higher risk MDS who were heavily pretreated. The median interval from MDS diagnosis was 28 months. Six pts were enrolled in cohort 1 (50 mg), 10 pts in cohort 2 (100 mg) (4 pts replaced (2 deaths unrelated to treatment, 1 infection, 1 progressive disease (PD)), 12 pts were enrolled in cohort 3 (150 mg) where 6 pts were replaced (5 PD and 1 infection), and to date, 3 pts are enrolled in cohort 4 (200 mg).

No protocol defined DLT have been encountered to date. No grade 3 or 4 treatment related adverse events have been reported. The most common adverse events that were deemed possibly, or probably related to study drug included fatigue (n=9), diarrhea (n=6), night sweats (n=3), headache (n=3), numbness (n=3). There were 2 pts with grade 2 pneumonia and grade 3 fatigue, and 2 grade 2 diarrhea events. Seven pts (23%) developed leukocytosis on treatment and 13 pts (42%) experienced an increase in circulating myeloblasts at some point during study treatment. Three of 27 pts developed higher grade bone marrow myelofibrosis (change from grade 0-1 to grade 2-3), one of whom received the 50 mg dose and 2 pts on the150 mg dose. Eleven pts (35%) progressed to AML, 9 out of 11 patients who progressed had RAEB-2 or RAEB-t and 5 had poor risk cytogenetics.

The median follow up duration is 23 months. The best response on study per IWG 2006 criteria include marrow CR (mCR) + Hematological improvement (HI) (6%, n=2), mCR (3%, n=1), HI (13%, n=4), stable disease (SD) (29%, n=9), PD (36%, n=11) and not evaluable for response (13%, n=4). The overall response rate (HI+) was 22% (7 out 31 pts) and 26% among pts evaluable for response (7 out of 27 pts). HI included 6 platelet responses and 1 erythroid response. Among 20 pts who were platelet transfusion dependent, 6 became transfusion independent (30%). The median duration of response was 3.3 months. The median duration of treatment is 2 months. The most common reasons for eltrombopag discontinuation were PD (48%) and infection (10%). Median OS was 5 months whereas median OS was 8 months among HI+ responders. The median LFS was 3.5 months.

Eltrombopag yielded modest responses in heavily treated higher risk MDS pts after HMA failure. Leukocytosis, increased circulating myeloblasts and myelofibrosis were observed in subsets of pts. Future development of eltrombopag as a single agent in MDS should be in lower risk MDS or in combination with HMA in higher risk MDS.

Off Label Use: Use of eltrombopag in MDS.