A phase IV study evaluating QT interval, pharmacokinetics, and safety following fractionated dosing of gemtuzumab ozogamicin in patients with relapsed/refractory CD33-positive acute myeloid leukemia

Purpose: Gemtuzumab ozogamicin (GO) is indicated for treatment of relapsed/refractory (R/R) acute myeloid leukemia (AML). The QT interval, pharmacokinetics (PK), and immunogenicity following the fractionated GO dosing regimen have not been previously assessed. This phase IV study was designed to obtain this information in patients with R/R AML. Methods: Patients aged ≥ 18 years with R/R AML received the fractionated dosing regimen of GO 3 mg/m² on Days 1, 4, and 7 of each cycle, up to 2 cycles. The primary endpoint was mean change from baseline in QT interval corrected for heart rate (QTc). Results: Fifty patients received ≥ 1 dose of GO during Cycle 1. The upper limit of the 2-sided 90% confidence interval for least squares mean differences in QTc using Fridericia’s formula (QTcF) was < 10 ms for all time points during Cycle 1. No patients had a post-baseline QTcF > 480 ms or a change from baseline > 60 ms. Treatment-emergent adverse events (TEAEs) occurred in 98% of patients; 54% were grade 3–4. The most common grade 3–4 TEAEs were febrile neutropenia (36%) and thrombocytopenia (18%). The PK profiles of both conjugated and unconjugated calicheamicin mirror that of total hP67.6 antibody. The incidence of antidrug antibodies (ADAs) and neutralizing antibodies was 12% and 2%, respectively. Conclusion: Fractionated GO dosing regimen (3 mg/m²/dose) is not predicted to pose a clinically significant safety risk for QT interval prolongation in patients with R/R AML. TEAEs are consistent with GO’s known safety profile, and ADA presence appears unassociated with potential safety issues. Trial registry: Clinicaltrials.gov ID: NCT03727750 (November 1, 2018).