title: The pharmacokinetics of letrozole in brain and brain tumor in rats with orthotopically implanted C6 glioma, assessed using intracerebral microdialysis.
abstract: OBJECTIVE
  Emerging evidence suggests that primary and metastatic brain tumors may be sensitive to hormonal manipulations. However, the pharmacokinetics of compounds against such targets in the brain and, more importantly, in the brain tumor are not well characterized. Here, we investigated the pharmacokinetics of letrozole, a third-generation aromatase inhibitor, in the normal brain and in orthotopically implanted C6 glioma in Sprague-Dawley rats.
  
  
  METHODS
  Intracerebral microdialysis was employed to determine the concentrations of unbound letrozole in the brain extracellular fluid (ECF) while simultaneously collecting blood samples (via jugular vein) to assess plasma levels of letrozole. Letrozole was administered intravenously at doses of 4, 6, 8 and 12 mg/kg, and ECF and blood samples were collected over 8 h. For assessing normal versus tumoral brain pharmacokinetics, letrozole (4 or 8 mg/Kg; i.v.) was administered 10 days after implantation of C6 glioma in the brain. Dual-probe intracerebral microdialysis was employed for assessing ECF samples from tumor-free and tumor-bearing regions of the brain.
  
  
  RESULTS
  Normal brain ECF and plasma C max and AUC0-8h increased linearly with letrozole doses up to 8 mg/kg dose, but at 12 mg/kg, the pharmacokinetics were nonlinear. The relative brain distribution coefficients, AUCECF/AUCplasma (ub), were 0.3-0.98. The tumoral uptake of letrozole was 1.5- to 2-fold higher relative to tumor-free region.
  
  
  CONCLUSIONS
  Thus, letrozole permeability across the blood brain barrier is high, and the exposure to the brain is dose dependent. Furthermore, the brain tumoral letrozole levels are markedly higher than those in the tumor-free regions, which underscore potential selectivity of its activity against tumor cells.
authors.affiliation: Department of Pharmaceutical Sciences, James L. Winkle College of Pharmacy, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: Nimita
authors.initials: N
authors.lastname: Dave
authors.forename: Gary A
authors.initials: GA
authors.lastname: Gudelsky
authors.forename: Pankaj B
authors.initials: PB
authors.lastname: Desai
mesh_terms: D000465:Algorithms; D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics*; D019540:Area Under Curve; D001921:Brain / Q000378:metabolism*; D001932:Brain Neoplasms / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D045604:Extracellular Fluid / Q000737:chemistry / Q000378:metabolism; D005260:Female; D005910:Glioma / Q000378:metabolism*; D006801:Humans; D000077289:Letrozole; D017551:Microdialysis; D009368:Neoplasm Transplantation; D009570:Nitriles / Q000493:pharmacokinetics*; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D014230:Triazoles / Q000493:pharmacokinetics*
chemical_list: D000970:Antineoplastic Agents; D009570:Nitriles; D014230:Triazoles; D000077289:Letrozole