A Phase 1/2 Study Of Blinatumomab In Pediatric Patients With Relapsed/Refractory B-Cell Precursor Acute Lymphoblastic Leukemia

Abstract Introduction Novel approaches are needed to treat pediatric relapsed/refractory B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Blinatumomab is a bispecific T-cell engager (BiTE®) antibody that has shown remission in an exploratory study of 36 adult patients with relapsed/refractory ALL. Primary toxicities in adults have been cytokine release syndrome (CRS) and central nervous system (CNS) related toxicity. We initiated a phase 1/2 multicenter study to identify, in the phase 1 part, the optimal dose of blinatumomab in pediatric patients with relapsed/refractory BCP-ALL. Methods In this ongoing study, eligible patients are <18 years old and must have BCP-ALL that is refractory, in second or later bone marrow relapse, or in any marrow relapse after allogeneic hematopoietic stem cell transplantation (HSCT). Blinatumomab is administered by continuous intravenous infusion over 28 days, followed by a 14-day treatment-free interval (up to five cycles). Data from the five doses that have been explored to date are presented. Maximum tolerated dose (MTD), defined as the highest dose level with less than two of six patients experiencing dose-limiting toxicity (DLT) within the first treatment cycle, is the primary endpoint in the phase 1 part of the study (rolling 6 design). Serum samples were collected for pharmacokinetics evaluation and cytokine measurement. Results In the phase 1 part of the study, 34 patients received a total of 56 cycles. Six (18%) patients had refractory disease and 6 (18%) had experienced at least two bone marrow relapses. Twenty-two (65%) patients had relapsed following HSCT. DLTs for dose levels 1 through 4 are summarized in the Table. The MTD for this patient population was established at 15 µg/m²/day. In order to reduce the risk of CRS, a dose of 5 µg/m²/day for 7 days escalating to 15 µg/m²/day for the remainder of the first cycle and all following cycles (5→15 µg/m²/day; dose level 5) was evaluated as recommended dose. None of the 11 patients treated at this dose level developed CRS and no grade 3 CNS-related adverse events (AEs) occurred. Across dose levels, the most common AEs regardless of causality were pyrexia (62% of patients), headache (35%), anemia (29%), and hypertension (29%). One patient treated at 5 µg/m²/day had a grade 3 seizure at the beginning of the second treatment cycle, which resolved clinically and showed no changes on MRI. Across all dose levels, 11 (32%) patients had complete remission (CR), one (3%) had hypocellular blast-free bone marrow, and two (6%) had partial remission within the first two treatment cycles, for an overall response rate of 41%. Some efficacy assessments are still ongoing, and full response data for the phase 1 part of the study will be available at the time of presentation. Two patients experienced hematologic relapse (one each at dose levels 2 and 3, during the fifth and third cycles, respectively). Pharmacokinetic parameters, such as steady-state concentration (Css) and clearance, appeared to be similar to those from adult patients with relapsed/refractory BCP-ALL who received body surface area-based blinatumomab dosing. Transient elevations of serum cytokines were observed mainly in the first two days after infusion start, in particular IL-6, IFN-gamma, IL-10, and, to a lesser extent, IL-2 and TNF-α. Conclusions In the ongoing phase 1 part of this study in pediatric patients with relapsed/refractory BCP-ALL, a dose of 15 µg/m²/day was established as MTD. Cytokine-release syndrome has been dose-limiting. Pharmacokinetic analysis at the recommended dose of 5→15 µg/m²/day is ongoing. This dose de-escalation strategy has been successful in ameliorating severe CRS to date. Blinatumomab treatment has shown promising antitumor activity in this relapsed/refractory patient population. Disclosures: von Stackelberg: Amgen Inc.: Honoraria. Zugmaier:Amgen Research (Munich) GmbH: Employment; Amgen Inc.: Equity Ownership. Rheingold:Novartis: Research Funding. Holland:Amgen Inc.: Employment; Amgen Inc.: Equity Ownership. Mergen:Amgen Research (Munich) GmbH: Employment; Amgen Inc.: Equity Ownership. Fischer:Amgen Research (Munich) GmbH: Employment; Amgen Inc.: Equity Ownership. Zhu:Amgen Inc.: Employment; Amgen Inc.: Equity Ownership. Hijazi:Amgen Research (Munich) GmbH: Employment; Amgen Inc.: Equity Ownership. Gore:Amgen Inc.: Travel expenses paid for DSMC meeting (Feb 2013) Other.

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