Phase I Study of Eltrombopag for Promoting Thrombopoiesis in Patients Undergoing Stem Cell Transplantation After Total Body Irradiation,

Prolonged intervals of thrombocytopenia are common after hematopoietic stem cell transplantation (HSCT), and platelet transfusions are the only effective therapy. Risk of thrombocytopenia is greater in patients (pts) receiving total body irradiation (TBI) in their conditioning regimen. Eltrombopag (ePag) is a small-molecule, nonpeptide oral agent that functions as an agonist of the thrombopoietin receptor. It is approved by FDA for the treatment of chronic ITP and is being developed as a treatment for thrombocytopenia of other various etiologies. We report results of an ongoing Phase I clinical trial assessing the safety, pharmacokinetics (PK) and maximum tolerated dose (MTD) of once daily oral ePag in pts undergoing HSCT with a conditioning regimen containing TBI ≥ 400 cGy.

A Phase I dose-escalation clinical trial was conducted to evaluate the safety and PK of ePag at 4 different dose levels: 75, 150, 225, and 300 mg, once daily for 27 days, starting 24–48 hours post HSCT to eligible pts ≥18 yrs old. Pts with various indications for stem cell transplantation, KPS ≥70%, and TBI ≥ 400 cGy were eligible. Pts receiving either an autologous (Auto) or allogeneic (Allo) HSCT from a sibling, related donor, or matched unrelated donor (MUD) were eligible. Stem cells from peripheral blood (PBSC) or bone marrow were permitted; however, cord blood transplant was not permitted. Pts at risk of thromboembolism, or with a history of thromboembolic disease in the preceding 6 months, were excluded. PK sampling was obtained over a 24 h period after the first dose of ePag, as well as during the second week of treatment (steady-state).

As of July 1 2011, a total of 10 subjects (4 AML, 2 lymphoma, 1 CML, 1 MDS, 1 myelofibrosis, and 1 CLL/SLL) were enrolled, and 9 completed protocol treatments. All 9 were PBSC transplants with 6 MUD, 2 Allo and 1 Auto. Three subjects were completed at each dose level up to 225 mg. Enrollment is continuing at the 300 mg dose level. To date, 6/9 are alive while 3/9 died of non-relapse related causes (CMV pneumonitis and respiratory failure in 1, and steroid refractory GI GvHD in 2, f/u interval: 4.4 – 6.9 mo). No dose limiting toxicities (DLTs) have been observed. Most common adverse events up to 225 mg dose level were related to standard stem cell transplantation, which included low blood counts, fatigue, headache, diarrhea, nausea, peripheral edema, hypoalbuminemia, hyperglycemia, hypocalcemia, and hypomagnesemia. There were 9 SAEs observed in 5 pts, which included infection (3/9), pulmonary embolism (PE) (1/9), acute renal failure (2/9), gastrointestinal (2/9), and ARDS (1/9). Most SAEs were considered unrelated or unlikely related to ePag treatment except for the PE, which was considered possibly related to ePag but not considered a DLT. This subject had other risk factors for PE and the PE occurred 9 days after ePag had stopped at a platelet count of 252K. Time to platelet engraftment and number of platelet transfusions were documented for each enrolled pt. PK sampling demonstrated a dose dependent increase in plasma concentration of ePag (Figure 1). PK parameters for the 75, 150, and 225 mg dose levels are summarized in Table 1.

Figure 1:

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Mean (± SD) plasma ePag concentration time profiles for 75, 150, and 225 mg dose levels from ELT112549

Figure 1:

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Mean (± SD) plasma ePag concentration time profiles for 75, 150, and 225 mg dose levels from ELT112549

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27-day once daily dosing of ePag to enhance platelet recovery for post-transplant thrombocytopenia is well tolerated, with no DLTs observed up to the 225 mg dose level to date. Most AEs were transplant related. PK and the plasma exposure of ePag appears dose proportional over the studied dose range after single-dose and steady-state administration. Once-daily administration of up to 225 mg ePag for the transplant population receiving TBI ≥ 400 cGy as part of the conditioning regimen appears to be safe and well tolerated.

The study is supported by Biomedical Advanced Research and Development Agency (BARDA), and by GlaxoSmithKline who also provided the study drug.

Off Label Use: Promacta (eltrombopag) is an oral TPO Receptor agonist approved for the treatment of chronic ITP. The study being reported in this abstract is a phase I MTD study to evaluate eltrombopag for promoting thrombopoiesis in patients undergoing Stem Cell Transplantation after Total Body Irradiation. Dawson:GlaxoSmithKline: Employment.