Absorption, Metabolism, and Excretion of Quizartinib (AC220), a FLT3 Tyrosine Kinase Inhibitor for Treatment of Acute Myeloid Leukemia, in Healthy Male Volunteers

Abstract 4327 Quizartinib (AC220) is an oral tyrosine kinase inhibitor that has shown promising activity in refractory/relapsed acute myeloid leukemia patients in a Phase 1 and a Phase 2 study. The absorption, metabolism, and excretion of quizartinib were characterized in healthy volunteers in a Phase 1 mass balance study. Six healthy males (mean ± SD age 29 ± 8.4 years) received a single oral dose of 60 mg quizartinib as a solution; approximately 1.6% of the total dose was labeled with 14C (approximately 100 μCi). Blood, plasma, urine, and feces were collected for 14 days (336 h) after dosing. Maximum mean ± SD blood radioactivity concentrations, reached 4 h after dosing, were 296 ± 67.4 ng equivalents/g. Maximum blood radioactivity concentrations in individual subjects occurred 4 h after dosing and ranged from 228 to 397 ng equivalents/g. Excretion of radioactivity was relatively consistent throughout the study. The maximum mean ± SD urinary concentration of radioactivity was 112 ± 52.3 ng equivalents/g at 8 to 24 hours after dosing, and the maximum mean ± SD fecal concentration of radioactivity was 51,100 ± 21,300 ng equivalents/g at 24 to 48 h after dosing. A mean ± SD of 1.64 ± 0.482% of the dose was recovered in urine, and 76.3 ± 6.23% was recovered in feces. The overall mean ± SD recovery of radioactivity in urine and feces was 78.0 ± 6.24% over the course of the study, with recovery from individual subjects ranging from 72.4% to 88.3%. Excretion of radioactivity was still ongoing at study completion (336 h). Recovery of <90% was not unexpected given the long half-life (approximately 3.5 days) of quizartinib. The major radiolabeled components of plasma were unchanged quizartinib and the oxidative metabolite AC886. Five additional metabolites in plasma were identified by LC-MS but could not be identified by measurement of radioactivity, because of low levels. Eighteen radioactive peaks in urine were detected, representing less than 0.09% of the administered dose, but their putative structures could not be identified because of low levels. Quizartinib was extensively metabolized, with the metabolites excreted primarily in feces, suggesting hepatobiliary excretion of radioactivity, non-biliary excretion into the gastrointestinal tract, or metabolism within the gastrointestinal tract. Forty-two radioactive peaks were detected in fecal extracts, of which unchanged quizartinib was a significant radioactive component (mean of 4.0% of the administered radioactive dose), and 15 metabolites, each representing a mean of 1.0% to 3.5% of the administered radioactive dose, were identified. Quizartinib was predominantly metabolized by phase I biotransformations, as was evident by the absence of any conjugates of quizartinib or of oxidative metabolites under the analytical conditions used to profile plasma, urine, and feces. Quizartinib was metabolized by multiple biotransformation pathways, including oxidation, reduction, dealkylation, deamination, and hydrolysis, and by combinations of these pathways. Quizartinib was well tolerated as a single 60 mg dose in this study. There were no clinically significant changes in vital signs, ECGs, or laboratory test results. Two subjects experienced adverse events. Grade 1 dry skin in 1 subject was considered to be unrelated to study treatment, and Grade 1 diarrhea in 1 subject was considered to be possibly related to treatment. The results of this study indicated that, in humans, quizartinib was orally available and predominantly eliminated in feces, with renal clearance as a minor elimination route, and that AC886 was the only major metabolite in the circulation. Disclosures: Li: Ambit Biosciences: Employment. Bresnahan:Ambit Biosciences: Employment. Gammon:Ambit Biosciences: Employment. Sanga:Covance Laboratories, Inc.: Employment. Hale:Covance, Inc.: Employment. Hashimoto:Astellas Pharma, Inc.: Employment. Gill:Astellas Pharma, Inc.: Employment. James:Ambit Biosciences: Employment.

Survival of patients with resistant Hodgkin's disease after polyclonal yttrium 90-labeled antiferritin treatment.

PURPOSE A follow-up study was initiated of patients with Hodgkin's disease who were treated with yttrium 90-labeled antiferritin. Prescription method, pharmacokinetics, acute and late side effects, and survival were evaluated. METHODS Patients had measurable disease and failed > or = two multiagent chemotherapy regimens previously (N = 44). All patients received 5-mCi indium 111-labeled antiferritin 2 mg intravenously and were scanned repeatedly by gamma camera. In five patients, polyclonal antiferritin (rabbit, pig, or baboon) failed to target the tumor. Thirty-nine patients were injected intravenously with 10-, 20-, 30-, 40-, or 50-mCi yttrium 90-labeled antiferritin 2 to 5 mg. Patients received between one and five cycles. Some patients were supported with 5 x 10(7) autologous bone marrow cells per kilogram. RESULTS Yttrium 90-labeled polyclonal antiferritin does not produce immunologic, pharmacologic, or microbiologic complications in vivo. Bone marrow toxicity is the only side effect observed. Overall response rate is 20 of 39, or 51%. Two patients had stable disease. A significant positive correlation is found between blood radioactivity level 1 hour after radioimmunoconjugate administration and subsequent response of Hodgkin's disease. A dosage in millicuries per kilogram provides a higher positive correlation with blood radioactivity levels 1 hour after administration than a dosage in millicuries per square meter of body-surface area or in total millicuries. Fifty percent of patients survive for > or = 6 months. CONCLUSION The low-dose protein used (2 to 5 mg) indicates that the high response rate is due to radiation and not to immunologic effects of the antibody. High-activity administrations followed by bone marrow transplantation are not required for tumor response. The therapeutic ratio of radiolabeled antiferritin is higher than the therapeutic ratio observed in most phase I studies of chemotherapeutic agents. This analysis does not identify a superior mode of treatment for patients with end-stage Hodgkin's disease. However, in a heavily pretreated patient population, prolonged survival is observed after relatively inexpensive treatment. Preclinical research with yttrium 90-labeled antiferritin indicates that significant increases in tumor dose can be obtained in the future without an increase in normal tissue toxicity.

Transendothelial transport of serum albumin: a quantitative immunocytochemical study

The steady-state distribution of endogenous albumin in mouse diaphragm was determined by quantitative postembedding protein A-gold immunocytochemistry using a specific anti-mouse albumin antibody. Labeling density was recorded over vascular lumen, endothelium, junctions, and subendothelial space. At equilibrium, the volume density of interstitial albumin was 18% of that in circulation. Despite this large difference in albumin concentration between capillary lumen and interstitium, plasmalemmal vesicles labeling was uniformly distributed across the endothelial profile. 68% of the junctions displayed labeling for albumin, which was however low and confined to the luminal and abluminal sides. The scarce labeling of the endothelial cell surface did not confirm the fiber matrix theory. The kinetics of albumin transcytosis was evaluated by injecting radioiodinated and DNP-tagged BSA. At 3, 10, 30, and 60 min, and 3, 5, and 24 h circulation time, blood radioactivity was measured and diaphragms were fixed and embedded. Anti-DNP antibodies were used to map the tracer in aforementioned compartments. A linear relationship between blood radioactivity and vascular labeling density was found, with a detection sensitivity approaching 1 gold particle per DNP-BSA molecule. Tracer presence over endothelial vesicles reached rapidly (10 min) a saturation value; initially localized near the luminal front, it evolved towards a uniform distribution across endothelium during the first hour. An hour was also needed to reach the saturation limit within the subendothelial space. Labeling of the junctions increased slowly, out of phase with the inferred transendothelial albumin fluxes. This suggests that they play little, if any, role in albumin transcytosis, which rather seems to proceed through the vesicular way.

A new method to evaluate extravascular albumin and blood cell accumulation in the lung

A method was developed to evaluate blood volume, accumulation of extravascular albumin (ALBev), and platelet (PL) or polymorphonuclear neutrophil (PMN) sequestration in lungs after challenge with inflammatory agents. Erythrocytes (RBC), albumin, and PL or PMN, labeled with 99mTc, 131I, and 111In,-respectively, were injected intravenously into anesthetized and ventilated guinea pigs. The different parameters were calculated from in vivo lung and blood radioactivity values. When N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) was injected intravenously at 10 micrograms.kg-1, lung RBC content dropped by 14.7 +/- 1.8% (SE; n = 10), indicating a reduced lung blood volume, ALBev rose to 15.0 +/- 3.2% of the initial albumin vascular content, and the circulating PMN were sequestered by 9.2 +/- 1.7%. A transient PL sequestration was also observed 1 min after the injection of fMLP (13.1 +/- 2.0%, n = 7). During the infusion of 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphorylcholine, the lung PL content rose dose dependently from 10.1 +/- 2.2% of the circulating pool with 3 ng.kg-1.min-1 to 54.9 +/- 20.1% with 44 ng.kg-1.min-1, the lung RBC content decreased by greater than 10%, and the ALBev increased beyond 16%. Our method allows the study of the correlations between cell entrapment and the variations of the albumin exchanges in the lung and may lead to a better understanding of the correlations between cell activation and edema.

Cerebral Blood Volume Measured with Inhaled C15O and Positron Emission Tomography

Local cerebral blood volume (CBV) has been measured previously with inhaled 11CO and positron emission tomography (PET). The model used assumes that equilibrium in tracer concentration has occurred between arterial and systemic venous blood before the PET measurement is made. To verify that this model may be used with the much shorter half-lived C15O, we have simultaneously measured arterial and venous blood radioactivity following C15O inhalation. Equilibrium occurred 95 ± 39 s after inhalation (n = 7). If the PET measurement is commenced prior to arteriovenous equilibrium, significant errors occur in calculated CBV. These data indicate that C15O may be used as a tracer for CBV measurement provided that emission data collection commences at ∼120 s after inhalation. Strict quality control measures must be maintained to minimize the contamination of administered C15O with 15O-labeled CO2.