title: Use of total and unbound imatinib and metabolite LC-MS/MS assay to understand individual responses in CML and GIST patients.
abstract: OBJECTIVE
  Trough total imatinib (t-IM) concentrations have been reported to be associated with therapeutic and toxic responses in patients with chronic myelogenous leukemia (CML) and gastrointestinal stromal tumor (GIST). Little is known about the relationships between effects and concentrations of either unbound imatinib (f-IM) or imatinib's major metabolite, N-desmethyl imatinib (NDI). In part, this is because of the lack of a single, validated, well-described clinically useful assay for these measurements. The authors report the development and application of such an assay.
  
  
  METHODS
  A single liquid-chromatography tandem-mass-spectrometry assay was used to monitor t-IM, f-IM, and t-NDI concentrations in CML and GIST patients treated at a tertiary German teaching hospital. The assay was also validated for measuring other kinase inhibitors, including t-nilotinib, sunitinib, and erlotinib. Ultrafiltration assays were validated and used to measure f-IM and to compare free fractions to plasma α1-acid glycoprotein concentrations (AGP).
  
  
  RESULTS
  The assays were linear over a working range (in micrograms per liter) of 8.4-8370, 8.3-4165, and 1.0-250 and had within- and between-run coefficient of variance of <7%, <12%, and <9% for t-IM, t-NDI, and f-IM, respectively. The f-IM assay was reproducible despite high (25.2%-31.6%) but concentration-independent binding to ultrafiltration devices. Clinically relevant results, such as nondetectable (ND) t-IM (<8.4 μg/L) in non-responders and >1500 μg/L in patients with major toxicity, were found. Of 156 total samples from 68 adult CML patients and 127 total samples from 42 adult GIST, only 48 samples from 22 CML patients and 40 samples from 20 GIST patients were trough samples with adequate dosing and collection information. More than half (27 of 48 CML and 24 of 40 GIST) had t-IM concentrations ≥10% below recommended target concentrations (1002 μg/L for CML and 1100 μg/L for GIST). Concentrations >50% over targets were also found in 6 of 48 CML and 4 of 40 GIST samples. Wide variations in concentrations of t-IM (range, ND to 2973 μg/L), t-NDI (range, ND to 659 μg/L), f-IM (range, 8.3-262 μg/L), and t-IM:f-IM ratios (range, 2.6%-14%) were found both between and within patients. A statistically significant association (Spearman correlation coefficient and P value for all samples, r = 0.290 and P = 0.023; for trough only, r = -0.585 and P = 0.028) was found between AGP and f-IM concentrations but wide interpatient and intrapatient variations made individual predictions unreliable.
  
  
  CONCLUSIONS
  The liquid-chromatography tandem-mass-spectrometry methods developed provided information useful to understand individual responses to therapy even though necessary sampling and dosing information was often not available. Wide unpredictable variations in t-IM, t-NDI, and f-IM were found. Clinical outcome trials are needed to examine whether f-IM or NDI monitoring can improve the ability to predict individual responses.
authors.affiliation: Central Laboratory, Department of Clinical Chemistry, University Medical Center, George-August-University, Goettingen, Germany. fstreit@med.uni-goettingen.de
authors.forename: Frank
authors.initials: F
authors.lastname: Streit
authors.forename: Lutz
authors.initials: L
authors.lastname: Binder
authors.forename: Angelika
authors.initials: A
authors.lastname: Hafke
authors.forename: Gunnar
authors.initials: G
authors.lastname: Brandhorst
authors.forename: Friederike
authors.initials: F
authors.lastname: Braulke
authors.forename: Detlef
authors.initials: D
authors.lastname: Haase
authors.forename: Thomas
authors.initials: T
authors.lastname: Armbrust
authors.forename: Silke
authors.initials: S
authors.lastname: Cameron
authors.forename: Giuliano
authors.initials: G
authors.lastname: Ramadori
authors.forename: Michael
authors.initials: M
authors.lastname: Oellerich
authors.forename: Philip
authors.initials: P
authors.lastname: Walson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000970:Antineoplastic Agents / Q000097:blood / Q000627:therapeutic use*; D001549:Benzamides; D002853:Chromatography, Liquid / Q000379:methods*; D005260:Female; D046152:Gastrointestinal Stromal Tumors / Q000097:blood / Q000188:drug therapy*; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000097:blood / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D010879:Piperazines / Q000097:blood / Q000627:therapeutic use*; D011743:Pyrimidines / Q000097:blood / Q000627:therapeutic use*; D053719:Tandem Mass Spectrometry / Q000379:methods*; D055815:Young Adult
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate