ASC4KIDS: A Multicenter, Open-Label, Phase Ib/II Study to Determine the Dose and Safety of Asciminib in Pediatric Patients with Chronic Myeloid Leukemia in the Chronic Phase

Background

Tyrosine kinase inhibitors (TKIs) are the standard of care for adult and pediatric patients with chronic myeloid leukemia in the chronic phase (CML-CP). More treatment options with improved efficacy and safety profiles are needed for pediatric patients. Asciminib is a first-in-class allosteric inhibitor of ABL (non-receptor tyrosine) kinases, specifically targeting the ABL myristoyl pocket (STAMP), and does not inhibit other protein kinases. Asciminib was approved by the US Food and Drug Administration (FDA) with subsequent approvals worldwide for patients aged ≥18 years with Philadelphia chromosome-positive (Ph+) CML-CP treated with ≥2 prior TKIs in October 2021. Asciminib 40 mg twice daily (bid) has demonstrated improved major molecular response rates (25.5% vs 13.2% at week 24) and a favorable safety profile compared with bosutinib 500 mg once daily (qd) in adult patients with Ph+ CML-CP in the phase 3 ASCEMBL study (NCT03106779). This study aims to characterize the pharmacokinetics (PK), long-term safety profile, and antileukemic effects of asciminib in pediatric patients and identify a pediatric formulation dose that will lead to asciminib exposure comparable to 80 mg qd or 40 mg bid in adult patients.

Methods

This multicenter, open-label study (NCT04925479) includes patients aged 1 to <18 years with Ph+ CML-CP, without a BCR::ABL1 T315I mutation, treated with ≥1 prior TKI. For the pediatric formulation group, at least 15 patients will be included in each of the two age groups (1 to <12 years and 12 to <18 years), consisting of Part 1, 2 and 3. The study started with an exploratory adult formulation group of Adolescent patients (aged 14 to <18 years, body weight ≥40 kg) treated with the adult formulation dose (40 mg bid or 80 mg qd tablet) under fasting conditions. The primary endpoint includes PK parameters; secondary endpoints include: hematologic and molecular responses, safety, and acceptability/palatability of the pediatric formulations.

Part 1 (dose-determining cohort): 4 to 6 patients will receive the asciminib pediatric formulation bid (a mini-tablet of 1.3 mg/kg with food) to assess safety, and to assess if the exposure in pediatric patients is comparable to exposure with the adult formulation over the first 28 days (patients either from pediatric or adult categories). After the interim analysis, if a dose adjustment is required, an additional 4 to 6 patients will be assessed at an adjusted dose.

Part 2 (expansion cohort, 40 mg bid regimen): 14 to 16 patients will receive the dose determined in part 1. The second interim PK and safety analysis will be conducted after all patients from parts 1 and 2 complete 28 days of treatment.

Part 3 (expansion cohort, 80 mg qd regimen): 10 patients (5 from each age group) will receive the same total daily dose of asciminib qd.

The PK, safety profile, and pharmacodynamic endpoints will be assessed for the bid regimen after all patients in parts 1 and 2 complete 52 weeks of treatment. The primary analysis for the combined bid and qd regimen will be performed after all patients complete 52 weeks of treatment (total treatment period: 5 years [ Figure]). A final analysis will be performed after all patients complete treatment. Patients who discontinue treatment early will be followed up for survival until the end of the study.

There are 32 study sites open out of planned 35 study sites in 14 countries worldwide.

The exploratory and the pediatric formulation groups recruited 4 patients and 9 patients, respectively, as of June 07, 2023, with a total of 13 patients in the study. The study is still recruiting.

This study will determine a pediatric dose for asciminib and support a strategy of full extrapolation from adult data to use in the pediatric patients with CML-CP.