title: Determination of doxorubicin levels in whole tumor and tumor nuclei in murine breast cancer tumors.
abstract: OBJECTIVE
  Pharmacokinetic studies on liposomal drugs have previously measured total drug levels in tumors, which include non-bioavailable drug. However, drugs must be released from liposomes to have activity. We have developed a method for measuring levels of bioavailable (released) doxorubicin in vivo in tumors that will allow therapeutic activity to be correlated with bioavailable drug levels.
  
  
  METHODS
  Mice orthotopically implanted with mammary carcinoma (4T1) were injected i.v. 10 days after implantation with free doxorubicin or formulations of liposomal doxorubicin with different drug release rates. Tumors were excised at various times after injection, and total tumor doxorubicin levels were determined by acidified isopropanol extraction of whole tumor homogenates. Bioavailable doxorubicin levels were determined by extraction of doxorubicin from isolated tumor nuclei.
  
  
  RESULTS
  Free doxorubicin had high levels of bioavailability in tumor tissue; 95% of the total doxorubicin in tumors was bound to nuclear DNA by 24 hours after injection. Administration of Doxil, a slow release liposomal formulation of doxorubicin, gave an area under the time-versus-concentration curve (AUC) for total doxorubicin 7 days after injection that was 87-fold higher than that obtained for free doxorubicin, and 49% of the liposomal doxorubicin was bioavailable. For liposomes with a more rapid doxorubicin release rate, by 7 days after injection, the AUC(0-7 days) for total doxorubicin was only 14-fold higher than that for free doxorubicin and only 27% of liposomal doxorubicin was bioavailable.
  
  
  CONCLUSIONS
  This technique allows correlations to be made between drug bioavailability and therapeutic activity and will help in the rational design of drug carriers.
authors.affiliation: Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Kimberley M
authors.initials: KM
authors.lastname: Laginha
authors.forename: Sylvia
authors.initials: S
authors.lastname: Verwoert
authors.forename: Gregory J R
authors.initials: GJ
authors.lastname: Charrois
authors.forename: Theresa M
authors.initials: TM
authors.lastname: Allen
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000737:chemistry / Q000493:pharmacokinetics*; D019540:Area Under Curve; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D004317:Doxorubicin / Q000737:chemistry / Q000493:pharmacokinetics*; D005260:Female; D008081:Liposomes / Q000737:chemistry; D015674:Mammary Neoplasms, Animal / Q000188:drug therapy* / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D013997:Time Factors
chemical_list: D000903:Antibiotics, Antineoplastic; D008081:Liposomes; D004317:Doxorubicin