Initial Results from a Phase 2/3 Study of Recombinant Erwinia Asparaginase (JZP458) in Patients with Acute Lymphoblastic Leukemia (ALL)/Lymphoblastic Lymphoma (LBL) Who Are Allergic/Hypersensitive to E. coli-Derived Asparaginases

Background: In patients with ALL, inability to receive L-asparaginase therapy due to hypersensitivity is associated with higher relapse risk (Gupta S, et al. J Clin Oncol. 2020). JZP458 is a recombinant Erwinia asparaginase derived from a novel Pseudomonas fluorescens expression platform to produce a reliable supply of enzyme with minimal immunologic cross-reactivity to E. coli-derived asparaginases. It has an amino acid sequence identical to that of native Erwinia asparaginase and its activity on asparagine is comparable based on in vitro measurements. This report includes initial analyses from the phase 2/3 open-label, multicenter, confirmatory pharmacokinetic (PK) and safety study (NCT04145531) of JZP458 in patients with ALL/LBL who developed hypersensitivity or silent inactivation to a long-acting E. coli-derived asparaginase.

Methods: For eligible patients, each remaining course of long-acting E. coli-derived asparaginase was substituted by six doses of intramuscular (IM) JZP458 on a Monday/Wednesday/Friday (M/W/F) schedule. The primary efficacy endpoint of the trial was evaluated by the proportion of patients with the last 72-hr (primary endpoint) and last 48-hr (key secondary endpoint) nadir serum asparaginase activity (NSAA) level ≥0.1 IU/mL during the first treatment course. Cohort 1a started with 25 mg/m ² IM JZP458 (M/W/F) and Cohort 1b explored a higher dose of 37.5 mg/m ² IM M/W/F. A preliminary population pharmacokinetic (PPK) model using Cohort 1a and 1b data predicted that a regimen of 25 mg/m ² (M/W) and 50 mg/m ² (F) would be optimal to support M/W/F dosing and Cohort 1c was initiated using this regimen.

Results: This initial report (data cutoff of Jan 11, 2021) provides data from 102 study patients enrolled in Cohort 1a (n=33, 51.5% male), 1b (n=53, out of 87 patients enrolled, 62.3% male), and 1c (n=16, out of 52 patients enrolled, 50.0 % male). The median (range) number of courses received in Cohorts 1a, 1b, and 1c as of the data cutoff was 4 (1, 14), 3 (1, 12), and 1 (1, 2), respectively, and 53% of patients were ongoing in treatment. The mean serum asparaginase activity (SAA) levels (95% confidence intervals [CIs]) for evaluable patients in Cohorts 1a, 1b, and 1c at 48 hrs were 0.4489 IU/mL (0.3720, 0.5258), 0.8376 IU/mL (0.6813, 0.9939), and 0.5085 IU/mL (0.3261, 0.6908); and at 72 hrs were 0.1543 IU/mL (0.1162, 0.1924), 0.3000IU/mL (0.2269, 0.3730), and 0.3579 IU/mL (0.2184, 0.4974). The proportion of patients achieving NSAA ≥0.1 IU/mL at 48 and 72 hr time points are presented in Table 1. PPK modeling and simulation analysis suggested that JZP458 given IM as 25 mg/m ² on M/W and 50 mg/m ² on F was expected to achieve NSAA levels ≥0.1 IU/mL in 99.8% of patients (95% CI: 99.6%, 100%) at 48 hours and 97.3% of patients (95% CI: 96.5%, 98.0%) at 72 hours.

Grade 3 or higher treatment-emergent adverse events, regardless of causality, occurred in 73/102 (72%) patients. Adverse drug reactions (ADRs) are shown in Table 2. These ADRs are consistent with the safety profile observed with other asparaginases.

Conclusions: The JZP458 IM dosing regimen of 25 mg/m ² M and W, and 50 mg/m ² F demonstrates a positive benefit:risk profile, achieving SAA levels ≥0.1 IU/mL in >90% of patients studied at both 48- and 72-hrs and a safety profile that is consistent with what has been observed in published literature on asparaginases.

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