Safety and Pharmacokinetics of Calaspargase Pegol in Adults with Newly Diagnosed Philadelphia-Negative ALL: A Phase 2/3 Study

Background: Overall survival (OS) in adults with ALL remains around 40%, but treatment with asparaginase (ASP)-containing pediatric-inspired regimens demonstrated a 3- or 4-year OS of 67-76%, including in patients with T-cell ALL, with manageable toxicities (Geyer 2020, Stock 2019, DeAngelo 2015). Recent studies in adults with reduced pegaspargase (PEG-ASP) doses showed survival outcomes similar to those with standard doses, with reduced toxicities, including pancreatitis, hepatic and thromboembolic events (Derman 2020, Patel 2020).

Calaspargase pegol (ASPARLAS; Cal-PEG), similar to PEG-ASP, is an E. coli L-asparaginase covalently conjugated to monomethoxy polyethylene glycol, but with a more chemically stable succinimidyl carbonate linker, providing sustained asparagine depletion with less frequent dosing (every 21 days).

The efficacy and safety of Cal-PEG 2500 U/m ², vs PEG-ASP 2500 U/m ², was evaluated in 2 multicenter, randomized clinical trials (AALL07P4 [n=166] and DFCI 11-001 [n=239]) in newly diagnosed patients with ALL ≤21 years. Complete remission (CR), minimal residual disease (MRD), event-free survival (EFS), and OS were similar in both arms, with a 94% 5-year OS for Cal-PEG. The safety profile was consistent with that of PEG-ASP, with similar rates of hypersensitivity, pancreatitis, thrombosis, and hyperbilirubinemia (Vrooman 2021). Plasma asparaginase activity (PAA) levels were ≥0.1 U/mL 25 days after the induction dose in 95% of patients (Angiolillo 2014).

The absence of a standardized treatment and the inadequate outcome of adult treatment regimens, as well as a lack of targeted immunotherapies for T-ALL, highlight a critical unmet need for improved therapeutic approaches. A treatment protocol with less frequent Cal-PEG administration due to a more sustained asparaginase activity as well as age- and weight-based dose adjustments may improve clinical outcomes without added toxicities, and possibly extend the upper age limit of ASP-containing regimen for older adults.

Trial Design: We present a clinical trial design of an ongoing, multicenter, phase 2/3 study (NCT04817761) assessing the safety and anti-leukemic activity of Cal-PEG in newly diagnosed patients with Philadelphia-negative B- or T-cell ALL. Patients aged ≥22 years are eligible with ECOG performance status 0-2, no known history of pancreatitis, coagulopathy, CNS thrombosis or severe hepatic impairment.

This trial comprises two parts: dose confirmation run-in (part 1) and the expansion phase (part 2). Part 1 is open for enrollment and is the focus of this abstract.

Starting doses of Cal-PEG are based on the patients' age and BMI, with older patient groups assigned to lower doses (Table 1). A minimum of 4 (initial cohort) and up to 8 patients will be admitted per patient group. A total of 6 Cal-PEG doses will be administered during the treatment period as part of a multiagent chemotherapy regimen based on CALGB 10403 trial (Figure 1; Table 2), with end of treatment visit 1 year after the induction dose, and an additional 2 years of survival follow-up.

The primary endpoints in part 1 are 1) the safety of Cal-PEG, including incidence of pre-defined unacceptable toxicities (UT) within 30 days after the induction dose and 2) PAA profiles, including achieving PAA ≥0.1 U/mL at pre-specified time points. Secondary endpoints include immunogenicity, CR, end of induction and consolidation MRD, and 1-, 2- and 3-year EFS, disease-free survival, and OS.

Bayesian optimal interval design (BOIN) will be used to evaluate UT with specified boundaries for dose confirmation, expansion, or reduction. For each patient group, the observed UT rate at a dose level will be compared with the safety boundary (23.6%) and toxicity boundary (35.8%) to guide safety confirmation. PAA data from previous pediatric studies and each run-in cohort will also be used to confirm the tested dose through population PK modeling-based predictions. The decision to confirm or adjust the dose will be based on the accumulated safety and induction PAA data at end-of-cohort meetings with the investigators, sponsor and in consult with DSMB recommendations.

Part 1 started in July 2021 and will enroll ≈16-32 patients at multiple sites in the US. Part 2 will commence once the safety and PAA data from part 1 are analyzed and the expansion doses are confirmed. Up to 122 patients are expected to be enrolled in both phases of the trial.

Clinical trial information: NCT04817761

Figure 1

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Figure 1

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