Pharmacokinetics of Nilotinib in Pediatric Patients with Philadelphia Chromosome–Positive Chronic Myeloid Leukemia or Acute Lymphoblastic Leukemia

Study design and patient eligibility criteria

Eligible patients (aged 1–<18 years) had CML-CP or AP and were resistant to or intolerant of imatinib and/or dasatinib or had Ph⁺ ALL that had relapsed on or was refractory to standard therapy (see Supplementary Table S1 for key terms and abbreviations). A protocol amendment was made to include patients with newly diagnosed CML-CP, reflecting the approval of nilotinib for adult patients with newly diagnosed CML-CP as well as preliminary information from an interim analysis of this study; however, no patients with newly diagnosed disease were enrolled in the study. For patients with CML, resistance to imatinib/dasatinib was defined as increasing white blood cell or platelet counts (indicative of primary resistance or hematologic relapse), cytogenetic or molecular response consistent with suboptimal response or failure, progression to AP/BC, reappearance of Ph⁺ bone marrow cells following achievement of complete cytogenetic response (CCyR), increase of >30% in Ph⁺ cells in peripheral blood or bone marrow, or loss of molecular response. Intolerance of imatinib/dasatinib was defined as the development of adverse events (AE) requiring discontinuation of therapy. Patients must have had adequate heart, renal, hepatic, and pancreatic function as well as normal electrolyte levels. Patients receiving medications that inhibit or induce cytochrome P450 3A4 or that may prolong the QT interval and those who had received myelosuppressive chemotherapy within 3 weeks prior to study entry were not eligible. In the case of prior stem cell transplant or rescue without total body irradiation, patients with evidence of active GVHD and patients within 3 months of stem cell transplant were not eligible.

Patients were required to have a Karnofsky performance status of ≥50% (aged >10 years) or a Lansky performance status of ≥50% (aged ≤10 years). To evaluate the potential differences in pharmacokinetic parameters between younger and older pediatric patients, enrolled patients were assigned to 1 of 2 cohorts: aged 1 to <10 years or aged ≥10 to <18 years.

Study treatment

Nilotinib was administered orally in 50-, 150-, and/or 200-mg hard gelatin capsules at a dose of 230 mg/m² twice daily rounded to the nearest 50 mg (Supplementary Table S2), up to a maximum single dose of 400 mg. This dose was based on the recommended dose for adults of 400 mg twice daily, scaled to body surface area (BSA; ref. 11). Patients were not to consume food for ≥2 hours before the dose was taken, and no oral intake other than water was to be consumed for ≥1 hour after the dose was taken. Capsules were to be swallowed whole with water; patients with difficulty swallowing the capsule could disperse the contents in 1 teaspoon of applesauce (to be taken within 15 minutes of preparation; ref. 17).

Patients received a total of up to 12 or 24 cycles of nilotinib (28 days/cycle), depending on the protocol amendment under which they enrolled. On cycle 1 day 1, a single dose of nilotinib 230 mg/m² was administered to obtain a full 24-hour pharmacokinetic profile. Patients who completed ≥12 cycles of treatment and were benefiting from nilotinib could continue treatment in a rollover or compassionate-use study.

Study endpoints

The primary objective was to characterize the pharmacokinetic profile of nilotinib in pediatric patients, with a goal of identifying a dose for further pediatric studies to provide a nilotinib exposure with a dose equivalent to 400 mg twice daily in adult patients. Secondary objectives included assessment of safety and tolerability, evaluation of activity, and mutational analysis of peripheral blood by qRT-PCR.

Pharmacokinetic assessments

Single-dose pharmacokinetic parameters were calculated from full pharmacokinetic profiles obtained via serial sampling following a single administration of nilotinib 230 mg/m² on cycle 1 day 1. Steady-state pharmacokinetic parameters were calculated on the basis of trough concentrations of nilotinib on cycle 1 days 8, 15, 22, and 28 following twice-daily administration of nilotinib 230 mg/m². Serum concentrations of nilotinib were determined using a validated LC/MS-MS method (lower limit of quantification, 2.5 ng/mL). To assess steady-state pharmacokinetic parameters following multiple nilotinib doses, a sparse sampling approach (vs. more frequent serial sampling) was used to reduce the total blood sample volume required from pediatric patients.

Calculation of steady-state pharmacokinetic parameters

Area under the serum concentration–time curve (AUC) from time 0 to the end of the dosing interval at steady state (AUC_SS) was calculated as follows:

where AUC_tau is the AUC from time 0 to the end of the dosing interval at steady state, C_12h,SS is the average of the steady-state trough concentrations available on or after day 8, and AUC_0–12h is the AUC from 0 to 12 hours. Steady-state apparent systemic clearance (CL/F) was calculated as follows:

Steady-state CL/F was then scaled according to BSA to obtain the BSA-adjusted CL/F.

Efficacy assessments for CML

Response assessments were performed through the end of the study, and best responses on treatment were reported. In patients with CML, activity was evaluated on the basis of hematologic, cytogenetic, and molecular responses, with best responses reported per category. Complete hematologic response (CHR) was defined as white blood cell count of <10 × 10⁹/L, platelet count of <450 × 10⁹/L, basophils <5%, no blasts or promyelocytes in peripheral blood, myelocytes plus metamyelocytes <5% in peripheral blood, and no extramedullary involvement. Confirmed CHR was defined as CHR confirmed in 2 consecutive assessments ≥4 weeks apart.

Cytogenetic parameters included CCyR (0% Ph⁺ metaphases), partial cytogenetic response (PCyR; >0%–35% Ph⁺ metaphases), major cytogenetic response (0%–35% Ph⁺ metaphases; i.e., CCyR or PCyR), minor cytogenetic response (>35%–65% Ph⁺ metaphases), minimal cytogenetic response (>65%–95% Ph⁺ metaphases), and no cytogenetic response (>95% Ph⁺ metaphases). Evaluation of cytogenetic response required examination of ≥20 metaphases in each bone marrow sample.

Molecular response was assessed using a validated qRT-PCR assay for the e13a2/e14a2 BCR-ABL1 transcript; results were reported as a ratio of BCR-ABL1 transcripts to ABL1 control transcripts, standardized to the International Scale (BCR-ABL1^IS). Major molecular response (MMR) was defined as a 3-log reduction in BCR-ABL1 transcripts from a standardized baseline, or BCR-ABL1^IS ≤ 0.1%. If the e13a2/e14a2 transcript was not detected at baseline, samples were tested for the e1a2 transcript, although no molecular response on the IS could be determined; patients with e1a2 transcripts were monitored for treatment response based on changes in the BCR-ABL1/ABL1 ratio over time and via hematologic and cytogenetic responses.

Efficacy assessments for Ph⁺ ALL

Response assessments were performed through the end of the study, and best responses on treatment were reported. Complete remission with platelet recovery was defined as <5% blasts in bone marrow (M1 status), no blasts in peripheral blood, and platelet count of ≥100 × 10⁹/L. Complete remission with incomplete platelet recovery was defined as M1 status, no blasts in peripheral blood, and platelet count of <100 × 10⁹/L. Partial remission was defined as ≥5% to ≤25% blasts in bone marrow with adequate cellularity (M2 status) and complete disappearance of circulating blasts. Progressive disease was defined as >25% increase in blasts in bone marrow or peripheral blood, extramedullary involvement, >30% increase in Ph⁺ metaphases in bone marrow, or central nervous system involvement. Stable disease was defined as lack of complete remission, partial remission, or progressive disease.

Mutational analyses

Mutational analyses were performed via sequencing of peripheral blood and bone marrow samples collected at baseline and the end of treatment; samples collected at other time points were also assessed if clinically indicated. Emerging mutations were reported for the following 12 key BCR-ABL1 amino acid residues: M244, G250, Q252, Y253, E255, V299, F311, T315, F317, M351, F359, and H396. Mutations were classified as follows: resistant (T315I), less sensitive (Y253H, F359V, E255K, and E255V), or sensitive (all other mutations except T315I, Y253H, F359V, E255K, and E255V).

Safety assessments

Safety and tolerability were assessed through the end of the study and 30 days after study drug discontinuation based on AEs and clinical laboratory evaluations. AEs were graded using the NCI Common Terminology Criteria for Adverse Events version 3.0.

Statistical analyses

At least 14 pediatric patients were planned for initial enrollment (≥7/age group). Based upon moderate to high interpatient variability in nilotinib pharmacokinetic values (32%–64% for the AUC) and the safety profile of nilotinib in adult patients (7, 11), a 2-fold difference in the AUC or CL/F between pediatric and adult patients would be considered clinically meaningful. An interim analysis was performed to compare pharmacokinetic data from the first 7 patients in each group with data from a subset of adult patients in a phase 1 dose escalation study (11) who received nilotinib 400 mg twice daily. If a ≥2-fold difference in the AUC or CL/F was observed between a group and the reference data, 5 additional patients would be enrolled in that group because a sample size of ≥12 patients would be required to provide sufficient precision (0.237 in log scale) to characterize the mean AUC. Pharmacokinetic analyses included all patients who received nilotinib on cycle 1 day 1 and had an evaluable pharmacokinetic profile (defined as having completed cycle 1 and/or had pharmacokinetic sampling sufficient for pharmacokinetic characterization) or ≥1 evaluable steady-state trough concentration. Single-dose pharmacokinetic parameters following administration of nilotinib on cycle 1 day 1 were estimated using noncompartmental analysis based on individual concentration–time profiles. AUC_SS and CL/F were derived from drug accumulation ratios based on steady-state trough concentrations of nilotinib on cycle 1 days 8, 15, 22, and 28. Geometric means for AUC_SS and BSA-adjusted CL/F at steady state were compared with the reference data from adult patients treated with nilotinib 400 mg twice daily. Because the terminal phases of the concentration–time profiles on cycle 1 day 1 were not attainable due to the limitations of 24-hour sampling, some parameters (e.g., AUC to infinity) could not be determined. AUC_0–12h and AUC from time 0 to the last quantifiable concentration point (AUC_last; where last is 24 hours) for cycle 1 day 1 were reported instead. Because full concentration–time profiles after a single dose or at steady state were not available, steady-state parameters such as AUC_tau and CL/F could not be calculated using noncompartmental analysis, and population pharmacokinetic analysis could not be used to estimate these parameters due to the small sample size. Demographic and baseline characteristics and response parameters were summarized using descriptive statistics for all patients. Safety analyses included all patients who received ≥1 dose of nilotinib.

Ethics

This study was conducted in accordance with the principles of the Declaration of Helsinki as well as local laws and regulations. Written informed consent was provided by each patient's parent or legal guardian prior to participation in the study; in addition, assent was obtained from patients who were able to provide a signature or verbal assent. The study protocol and amendments were reviewed by an independent ethics committee or Institutional Review Board of each study center.

Data sharing statement

Novartis will not provide access to patient-level data if there is a reasonable likelihood that individual patients could be reidentified. Phase I studies, by their nature, present a high risk of patient reidentification; therefore, individual patient results for phase I studies cannot be shared. In addition, clinical data, in some cases, have been collected subject to contractual or consent provisions that prohibit transfer to third parties. Such restrictions may preclude granting access under these provisions. Where codevelopment agreements or other legal restrictions prevent companies from sharing particular data, companies will work with qualified requestors to provide summary information where possible.