Safety and Pharmacokinetics of Quizartinib Combination Therapy With Standard Induction and Consolidation Chemotherapy in Patients With Newly Diagnosed Acute Myeloid Leukemia: Results from Two Phase 1 Trials in Japan and China

Quizartinib is a potent, oral, second‐generation, selective type II FMS‐like receptor tyrosine kinase 3 (FLT3) inhibitor. It has shown improved overall survival in a randomized, multinational, Phase 3 (QuANTUM‐First) study in patients with FLT3‐internal tandem duplication (ITD)‐positive newly diagnosed acute myeloid leukemia. We conducted 2 Phase 1b studies in Japan and China to evaluate the safety, pharmacokinetics, and efficacy of quizartinib in combination with standard induction and consolidation chemotherapy in patients with newly diagnosed acute myeloid leukemia. Quizartinib was started at a dose level of 20 mg/day and then escalated to 40 mg/day, the dose used in the Phase 3 study. Seven patients were enrolled according to the 3 + 3 dose‐escalation method in each study, including 3 patients who were FLT3‐ITD positive. No dose‐limiting toxicities were observed at dose levels up to 40 mg/day in both studies. Grade 3 or higher, quizartinib‐related, treatment‐emergent adverse events included febrile neutropenia, hematologic toxicities, and infections. QT prolongation on electrocardiogram was observed in 5 patients. The pharmacokinetics of quizartinib and its metabolite AC886 were similar between the studies and consistent with previous findings in the United States. We confirmed the tolerability of Japanese and Chinese patients to the dose of quizartinib and chemotherapy regimens used in the QuANTUM‐First study.

Acute myeloid leukemia (AML) is the most common type of acute leukemia among adults worldwide, accounting for approximately 70% of all cases of leukemia in Japan. 1,2AML is more common in people aged 65 years or older, and its incidence is increasing over time, potentially partly because of the growing aging population. 3espite advances in treatments and the achievement of complete remission (CR) in 60%-85% of patients aged 60 years or less and 40%-60% of those aged greater than 60 years, many patients experience relapses. 4The long-term survival rate after relapse is low, with patients relapsing after allogeneic hematopoietic stem cell transplantation, showing a 1-year survival rate of 23%. 5 Mutations in the FMS-like receptor tyrosine kinase 3 (FLT3) gene are common in AML, with internal tandem duplication (ITD) detected in approximately 20%-30% of patients. 6,77][8] The assessment of genetic mutations, including those in the FLT3 gene, as prognostic factors has become increasingly important for risk assessment and in the treatment of AML. 9 Recently, FLT3-ITD was reclassified as an intermediate risk, regardless of the allelic ratio and coexistence of NPM1 mutations, 9 partly due to the contribution of the FLT3 inhibitor midostaurin, which prolonged OS in its pivotal clinical trial. 10uizartinib hydrochloride (quizartinib hereafter) is an oral, once-daily, potent, and selective secondgeneration type II FLT3 inhibitor that binds to the inactive kinase conformation of the receptor and thus exerts inhibitory activity against FLT3-ITD. 11AC886, the hydroxylated form of quizartinib, is the major circulating metabolite with comparable potency and selectivity against FLT3 to its parent drug. 12Chemical structures and in vitro profiles of both compounds can be found in a previous study. 12Quizartinib treatment significantly prolonged OS in patients with FLT3-ITDpositive relapsed/refractory AML in the global, Phase 3, QuANTUM-R study (NCT02039726). 136][17][18][19] Coadministration of cytochrome P450 (CYP) 3A inhibitors (ketoconazole or fluconazole) with quizartinib increased the area under the plasma concentration-time curve (AUC) and maximum plasma concentration (C max ) of quizartinib, especially with ketoconazole.The half-life was ex-tended, but the time to reach maximum plasma concentration (t max ) remained unchanged, except for AC886 when quizartinib was coadministered with ketoconazole. 17The effect of strong CYP3A inhibitors on quizartinib exposure has also been reported in a population PK analysis. 18An open-label, randomized, parallel-group study in healthy volunteers showed minimal effects of lansoprazole on the plasma concentrations of quizartinib and AC886. 19 Phase 1 dose-escalation study was conducted in 19 patients with newly diagnosed AML (9 patients were FLT3-ITD positive) in the United States (NCT01390337).20 Three dosing regimens of quizartinib were evaluated (40 mg/day for 14 days or 60 mg/day for 7 or 14 days), and the maximum tolerated dose (MTD) was identified as 40 mg/day for 14 days.20 Herein, we report the results of 2 Phase 1b studies conducted in Japan and China to confirm the safety, PK, and efficacy of quizartinib in combination with standard induction and consolidation chemotherapy in Japanese and Chinese patients with newly diagnosed AML.

Study Design
The clinical trial protocols for both studies were approved by the institutional review board of each participating institution (Table S1).The trials were conducted in accordance with the ethical principles of the Declaration of Helsinki, the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines, and applicable regulatory requirements.All patients provided written informed consent to participate in the study.
Two open-label, Phase 1b, 3 + 3 design, doseescalation studies were conducted to assess the safety, PK, and efficacy of quizartinib at dose levels of 20 mg/day (Dose Level 1) and 40 mg/day (Dose Level 2) in combination with standard chemotherapy (Figure 1).The AC220-A-J102 study (Japanese study) was a Phase 1b study conducted in 6 Japanese centers (Table S1) between August 2016 and October 2017 (NCT02834390).The AC220-A-A103 study (Chinese study) was a single-center, Phase 1b study conducted in China (Table S1) between November 2018 and March 2022 (NCT03723681).Quizartinib was administered at 2 dose levels; if the dose-escalation criteria were met at Dose Level 1, the study proceeded to Dose Level 2. Dose escalation in a single patient was not permitted.

Patients
These studies enrolled patients with AML, regardless of their FLT3-ITD status, who had not received prior treatment for AML.Patients aged 20-75 years (J102 study) or 18-70 years (A103 study) at the time of enrollment in the study with an Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0-2 were eligible for participation.Patients with a diagnosis of acute promyelocytic leukemia were excluded.Additionally, patients with a QT interval corrected with Fridericia's formula (QTcF) of greater than 450 milliseconds at baseline, significant uncontrolled cardiac conditions, or active acute or chronic systemic fungal, bacterial, or viral infections that were not well controlled by antifungal, antibacterial, or antiviral therapy, respectively, were excluded.The detailed inclusion and exclusion criteria are listed in Table S2.

Treatment
The induction and consolidation therapy regimens were designed to be consistent with the protocol of the QuANTUM-First study. 14nduction therapy comprised an intravenous infusion of cytarabine (100 mg/m 2 /day [200 mg/m 2 /day if allowed by the institutional or local standard]) on Days 1-7 and daunorubicin (60 mg/m 2 /day) or idarubicin (12 mg/m 2 /day) on Days 1-3 (7 + 3 regimen).Quizartinib (20 or 40 mg) was orally administered once daily, after the completion of cytarabine administration, from Day 8 to Day 21.If composite complete remission (CRc; Table S3) was achieved by Day 42 (J102 study) or Day 56 ± 3 days (A103 study), the treatment was to proceed to Cycle 1 of consolidation therapy.If blasts in the bone marrow were 5% or greater, Cycle 2 of induction therapy was to be conducted using the same regimen as Cycle 1, or a 5 + 2 regimen.Each cycle consisted of 28 days.
Up to 4 cycles of consolidation therapy comprised a total of 6 intravenous infusions of cytarabine (3.0 g/m 2 /12 hours for patients aged less than 60 years and 1.5 g/m 2 /12 hours for patients aged 60 years or greater) on Days 1, 3, and 5. Quizartinib (20 or 40 mg) was orally administered once daily, after the completion of cytarabine administration, from Day 6 to Day 19.Patients with CRc following consolidation therapy were permitted to discontinue study treatment and undergo hematopoietic stem cell transplantation.Patients who relapsed after achieving CRc discontinued the study.
Concomitant use of quizartinib with the following drugs was not allowed: drugs that may potentially prolong the QT/QTc interval and strong CYP3A4 inhibitors (both permitted at the investigator's discretion, if medically essential to prevent or treat infection), strong or moderate CYP3A4 inducers, and crude drugs and food products with CYP3A4-inhibiting orinducing properties (eg, foods and beverages containing St. John's wort or grapefruit).

Safety Assessments
Safety analyses included the assessments of treatmentemergent adverse events (TEAEs) and dose-limiting toxicities (DLTs).TEAEs were defined as adverse events that emerged or worsened after the first dose of the study treatment to 35 days after the last administration of the study treatment, or a related serious adverse event with onset >35 days after the last dose of the study treatment.DLTs were defined as quizartinibrelated toxicities (Table S4) assessed at each dose level in the first 3 patients from the first dose of quizartinib (Day 8) to Day 42 (J102 study) or Day 56 ± 3 days (A103 study) of the last induction treatment cycle or the day before the start of the first consolidation cycle, whichever was earlier.A 12-lead electrocardiogram (ECG) was performed before the enrollment (between Day −14 and Day 0), including QTcF assessment by triplicate ECG recordings obtained at approximately 2minute intervals and during the induction and consolidation cycles.

Pharmacokinetic Assessments
Concentrations of quizartinib and its metabolite AC886 in plasma were determined using a validated liquid chromatography-tandem mass spectrometry method, 19 with a lower quantification limit of 0.500 ng/mL for both quizartinib and AC886.Any value below the lower limit of quantification was treated as 0 ng/mL.PK parameters were calculated from the plasma concentrations of quizartinib and AC886.On Cycle 1, Day 8 (first quizartinib administration), C max , t max , and AUC during the dosing interval (AUC tau ) were calculated, and on Cycle 1, Day 21 (last quizartinib administration), C max at steady state, t max at steady state, and AUC tau at steady state were calculated.The accumulation ratio (AR) of C max (AR [C max ]) and AUC tau (AR [AUC tau ]) was calculated by dividing the parameters on Day 21 by those on Day 8.

Efficacy Assessments
The efficacy response was evaluated based on bone marrow assessment, neutrophil count, and platelet count in the peripheral blood and categorized as CR, CR with incomplete hematologic recovery, CR with incomplete platelet recovery, partial remission (PR), and no response (NR) in the J102 study, and CR, CR with incomplete hematologic recovery, PR, and NR in the A103 study, in accordance with the response criteria defined in Table S3.Efficacy

Statistical Analysis
The safety, PK, and tumor response data were tabulated as descriptive statistics by study, using each relevant analysis set.The safety analysis set comprised patients who received at least 1 dose of quizartinib.The MTD analysis set comprised patients who received at least 1 quizartinib dose in the induction phase; patients were excluded from the MTD analysis set if quizartinib was administered for 9 days or less.The PK analysis set comprised patients who received at least 1 quizartinib dose and had available plasma concentration data.The efficacy analysis set comprised patients who received at least 1 quizartinib dose and had available tumor response data assessed at least at 1 time point after the first dose of quizartinib (Table S5).For tumor response rates, 95% confidence intervals (CIs) using the Wilson score method were also provided along with descriptive statistics.Statistical analyses were performed using SAS Version 9.2 or higher (SAS Institute Inc.) and R Version 4.0.5 (R Foundation for Statistical Computing).PK analysis was performed using Phoenix WinNonlin Version 6.4 (Certara, Inc.).

Patient Demographics
In each study, 7 patients were individually enrolled and received at least 1 quizartinib dose.Four patients were treated at Dose Level 1 (20 mg/day), and 3 patients were treated at Dose Level 2 (40 mg/day) in each trial (Table 1).In the J102 study, 4 female and 3 male patients were treated; the median age was 62 (range, 34-68) years; 5 patients had an ECOG PS of 0, and 2 patients had an ECOG PS of 1.In the A103 study, 3 female and 4 male patients were treated; the median age was 39 (range, 23-47) years; all patients had an ECOG PS of 1 at baseline.FLT3-ITD was positive in 1 patient at Dose Level 2 in the J102 study and in 1 patient at each dose level in the A103 study (Table 1).

Safety
The mean relative dose intensities in the induction phase of the J102 study were 100% and 94.1% for the 20 and 40 mg/day doses, respectively.In the consolidation phase of the J102 study, the mean relative dose intensity was 100% at both dose levels.In the A103 study, the mean relative dose intensities in the induction phase were 91.1% and 96.4% for 20 and 40 mg/day, respectively.In the consolidation phase of the A103 study, the mean relative dose intensities were 98.2% and 100% for the 20 and 40 mg/day doses, respectively.
No DLTs were reported in either the J102 or the A103 study, and MTD was not reached at doses up to 40 mg/day.In the J102 study, 7 patients (100%) and 3 patients (100%) experienced Grade 3 or greater TEAEs in the induction and consolidation phases, respectively.In the A103 study, Grade 3 or greater TEAEs were observed in 3 patients (75%) and 3 patients (100%) at Dose Levels 1 (20 mg/day) and 2 (40 mg/day) in the induction phase, respectively.In addition, in the A103 study, all patients (100%) experienced Grade 3 or greater TEAEs in the consolidation phase at both dose levels (Table S6).
In the J102 study, the most commonly reported TEAEs in the entire period were febrile neutropenia, alopecia, decreased appetite, gamma-glutamyl transferase increased, upper abdominal pain, and nausea.The most common Grade 3 or greater TEAE was febrile neutropenia in both treatment phases at both dose levels (Table 2 and Table S7).Two patients experienced serious TEAEs during the induction phase: No cases were detected with AML (M4Eo, CBFB-MYH11), APL (M3, M3v), AML (DEK-NUP214), AML (RPN1-EVI1), AML (RBM15-MKL1), AML (NPM1), or AML (CEBPA).Moreover, no cases of acute erythroid leukemia, acute megakaryoblastic leukemia, acute basophilic leukemia, or acute panmyelosis with myelofibrosis were included.In the A103 study, the most commonly observed TEAEs in the entire period were leukopenia, neutropenia, thrombocytopenia, gingivitis, pneumonia, and alanine aminotransferase increased.The most common Grade 3 or greater TEAEs were leukopenia and thrombocytopenia in both treatment phases at both dose levels (Table 2 and Table S7).One patient (25%) receiving Dose Level 1 had Grade 5 sepsis (not related to the study drug).One patient experienced other serious TEAEs during the induction phase-anaphylactic reaction and streptococcal sepsis (1 patient at Dose Level 2)-but neither of these serious TEAEs was related to quizartinib.Three patients experienced serious TEAEs during the consolidation phase: kidney infection, hepatic infection, and splenic infection (1 patient at Dose Level 1; these 3 events were considered quizartinib related) and anal fistula, Enterobacter sepsis, pneumonia (2 patients at Dose Level 2; pneumonia was considered quizartinib related).These serious TEAEs were resolved.

Prolongation of QTcF on ECG
In the J102 study, QTcF prolongation on ECG, which was defined as QTcF values of greater than 450 milliseconds or change from baseline by greater than 30 milliseconds, was observed in 3 patients at Dose Level 2 (40 mg/day).In the A103 study, QTcF prolongation on ECG was observed in 1 patient each at Dose Levels 1 (20 mg/day) and 2 (40 mg/day).All 5 patients who developed QTcF prolongation on ECG had QTcF values of greater than 450-480 milliseconds or less (Table 3).

Pharmacokinetics
Figure 2 shows the time course of the plasma concentration of quizartinib and AC886 during the induction phase of treatment.In the J102 study, the mean C max of quizartinib on Day 8 after the first dose was 43.4 ng/mL at Dose Level 1 (20 mg/day) and 93.6 ng/mL at Dose Level 2 (40 mg/day).The median t max was 3.03 hours at Dose Level 1 and 2.17 hours at Dose Level 2. In the A103 study, the mean C max of quizartinib on Day 8 was 40.9 ng/mL at Dose Level 1 and 70.4 ng/mL at Dose Level 2. The median t max was 2.02 hours at Dose Level 1 and 3.98 hours at Dose Level 2 (Table 4).In the J102 study, the mean C max of quizartinib on Day 21 after the first dose was 72.6 ng/mL at Dose Level 1 (20 mg/day) and 223 ng/mL at Dose Level 2 (40 mg/day).The median t max was 4.03 hours at Dose Level 1 and 4.08 hours at Dose Level 2. In the A103 study, the mean C max on Day 21 was 94.2 ng/mL at Dose Level 1 and 234 ng/mL at Dose Level 2. The median t max was 1.95 hours at Dose Level 1 and 1.98 hours at Dose Level 2 (Table 4).
The C max and AUC tau of quizartinib and AC886 increased in a dose-dependent manner in both studies, whereas no notable difference was observed in the t max between the 20 and 40 mg/day dose groups.In both studies, C max and AUC tau increased from Day 8 to Day 21.In the J102 study, the mean AR (C max ) and AR (AUC tau ) values of quizartinib were 1.52 and 2.37, respectively, at Dose Level 1 and 1.98 and 2.84, respectively, at Dose Level 2 (N = 2).In the A103    4).The distributions of the dose-normalized C max and AUC tau on Day 21 were similar in both studies (Figure 3).

Efficacy
In the J102 study, 3 of 4 patients at Dose Level 1 (20 mg/day) achieved CRc (75%), and the remaining patient had PR, yielding a response rate of 100% (95% CI, 51.0-100.0).Two of 3 patients at Dose Level 2 (40 mg/day) achieved CRc (66.7%), and the remaining patient had NR, yielding a response rate of 66.7% (95% CI, 20.8-93.9).In the A103 study, 2 of 3 patients at Dose Level 1 achieved CRc, and the remaining patient had PR, yielding a response rate of 100.0%(95% CI, 43.9-100.0).All 3 patients at Dose Level 2 achieved CRc (Table 5).Among the 2 patients with FLT3-ITD in the A103 study, 1 patient achieved CR at Dose Level 2 (40 mg/day).One patient with FLT3-ITD who received Dose Level 1 (20 mg/day) in the A103 study was excluded from the efficacy analysis because of missing efficacy data.

Discussion
We performed 2 Phase 1 trials to confirm the safety and PK of quizartinib in combination with standard induction and consolidation chemotherapy in Japanese and Chinese patients with newly diagnosed AML.
The 2 dose levels assessed (20 and 40 mg/day for 14 days) were generally well tolerated in both studies.The tolerability and safety profiles observed in our studies are generally consistent with those reported in previous studies. 14,20In both studies, MTD was not reached at doses of up to 40 mg/day, and the most common TEAEs were hematologic, including febrile neutropenia, leukopenia, thrombocytopenia, and anemia, with similar trends in both studies.
The common quizartinib-related Grade 3 or greater TEAEs were infections (pneumonia and staphylococcal bacteremia) and QT prolongation, consistent with those reported in previous studies involving patients with newly diagnosed AML. 14,20Previously, quizartinib and its metabolite AC886 were reported to induce increases in QTcF in a dose-and concentrationdependent manner in patients with relapsed/refractory AML. 21QT prolongation with quizartinib has been shown to be manageable with dose modification and correction of electrolyte abnormalities. 13,14As reported previously, dose reduction of quizartinib is necessary in patients if a strong CYP3A inhibitor is concomitantly administered because such inhibitors increase the plasma concentration of quizartinib. 17,21urthermore, the J102 and A103 studies showed that the PK profiles of quizartinib and its metabolite AC886 displayed similar trends at the initial dosing and steady state in these patient populations.The PK profiles and dose-normalized PK parameters of quizartinib and AC886 were similar, and the distributions of the PK parameters were consistent with those in a previous Phase 1 study conducted in the United States. 20In addition, a population PK analysis that involved 13 Phase 1-3 clinical studies of quizartinib found that Asian race or the region of origin was not a significant covariate on either quizartinib or AC886 PK parameters.In the global, Phase 3, QuANTUM-First study, the distribution of empirical Bayes estimates of the individual steadystate AUC tau and steady-state C max values across region/country subgroups generally overlapped with each other. 22The results of the PK analysis in our studies are fairly consistent with those of the previous study in the United States and the population PK analysis. 20,22s described above, the tolerability, safety, and PK profiles in the current Japanese and Chinese Phase 1b studies are generally consistent with those in a previous Phase 1 dose-escalation study conducted in the United States that included White individuals and Black or African American individuals. 20These findings support the hypothesis that the 40 mg/day regimen in combination with standard chemotherapy employed for the QuANTUM-First study could be applicable to Japanese and Chinese patient populations.The QuANTUM-First study met its primary end point and showed clinically meaningful and statistically significant OS improvement, demonstrating the appropriateness of quizartinib dosing regimens in patients with FLT3-ITD-positive newly diagnosed AML.Furthermore, the QuANTUM-First study, which included 100% of patients with FLT3-ITD-positive AML, did not employ a quizartinib dose of above 40 mg/day in either the induction or the consolidation phase and demonstrated clinical benefit and acceptable safety profile of the 40 mg/day regimen. 14Therefore, MTD determination for greater than 40-mg doses of quizartinib was not necessary in Japanese and Chinese patients with FLT3-ITD-positive newly diagnosed AML.
The antileukemic response of 40 mg/day quizartinib in the current studies is consistent with that observed in a Phase 1 study in the United States and the global, Phase 3, QuANTUM-First study. 14,20However, the small sample size and limited number of patients with FLT3-ITD mutation hindered the detection of a correlation between FLT3-ITD status and the efficacy of quizartinib in the Japanese and Chinese populations.

Conclusions
Our results confirmed that treatment with 40 mg/day of quizartinib in combination with standard induction and consolidation chemotherapy, which was used in the QuANTUM-First study, is applicable to Japanese and Chinese patients with newly diagnosed AML.
was assessed on Day 21 of Cycle 1 and Cycle 2 in the induction phase.In the consolidation phase, efficacy was assessed on Days 21-42 (J102 study) or Days 21-56 ± 3 days (A103 study) of Cycle 1 and Day 21 (J102 study) or Days 21-56 ± 3 days (A103 study) of Cycle 4 (or last cycle).
; QT, interval between the start of the Q wave and the end of the T wave; QTcF, QT interval corrected with Fridericia's formula; RR, the time elapsed between 2 successive R-waves of the QRS signal on the electrocardiogram.a At Dose Level 2 (40 mg/day) in the J102 study, the baseline values of ECG parameters in 1 patient were excluded from the analysis due to the deviation of the time window.Safety analysis set.QTcF = QT/(RR/1000) 1/3 .

Figure 2 .
Figure 2. Time course of the plasma concentration of quizartinib and AC886 during the induction phase of treatment.Data were obtained on Day 21 of the induction phase, which was Day 14 of quizartinib treatment.Dose of quizartinib (17.7 mg [Dose Level 1]) and 35.4 mg [Dose Level 2]) is shown as free base form.SD, standard deviation.

Figure 3 .
Figure 3. Scatter plot depicting dose-normalized PK parameters of quizartinib and AC886.Data were obtained on Day 21 of the induction phase, which was Day 14 of quizartinib treatment.AUC, area under the curve; C max , maximum serum concentration; PK, pharmacokinetic.

Table 2 .
Most Frequent TEAEs During the Induction and Consolidation Phases of Treatment AE, adverse event; MedDRA, Medical Dictionary for Regulatory Activities; PT, Preferred Term; TEAE, treatment-emergent adverse event.PTs are coded using MedDRA Version 20.1 in the J102 and MedDRA Version 24.0 in the A103 study.No Grade 5 (death related to AE) TEAEs were reported in the J102 study.Safety analysis set.pneumonia (1 patient at Dose Level 2 [40 mg/day]) and staphylococcal bacteremia (1 patient at Dose Level 2 [40 mg/day]; quizartinib related).These serious TEAEs were resolved.Grade 5 TEAEs were not observed.

Table 3 .
Incidences of QTcF Prolongation from Baseline During the Induction and Consolidation Phases

Table 5 .
Best Overall Response and Response Rates