title: Relationship between topotecan systemic exposure and tumor response in human neuroblastoma xenografts.
abstract: BACKGROUND
  Topotecan is a topoisomerase I inhibitor with activity against xenografts of childhood solid tumors and established clinical activity against neuroblastoma and rhabdomyosarcoma. We have studied the relationship between systemic exposure to and the antitumor activity of topotecan lactone (the active form of the drug) in the xenograft models. Furthermore, we determined whether the responses seen in these models occur at systemic exposure levels that are tolerable in children.
  
  
  METHODS
  Neuroblastoma xenografts derived from the tumors of six different patients were established subcutaneously in immune-deprived mice. Topotecan was administered by intravenous bolus injection 5 days a week for 2 consecutive weeks, repeated every 21 days for three cycles. The minimum daily doses that induced complete responses (CRs) and partial responses (PRs) were determined. Topotecan lactone pharmacokinetic studies were performed in both tumor-bearing and nontumor-bearing mice.
  
  
  RESULTS
  The minimum doses associated with CRs and PRs in four of the six neuroblastoma xenografts were 0.61 and 0.36 mg/kg body weight, respectively. The topotecan lactone single-day systemic exposures associated with these doses were 88 and 52 ng x hr/mL, respectively. There was an approximately sixfold difference in topotecan lactone systemic exposure (290 ng x hr/mL versus 52 ng x hr/mL) associated with achieving CRs in the least-sensitive and most-sensitive tumors, respectively.
  
  
  CONCLUSIONS
  Neuroblastoma xenografts are highly sensitive to topotecan therapy, and responses in mice are achieved at systemic exposures similar to those that are clinically effective and tolerable in children. These results support the concept of deriving preclinical data relating systemic exposure to antitumor activity in xenograft models. Such data may be valuable in making informed decisions regarding the clinical development of new agents.
authors.affiliation: Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, TN 38105-2974, USA.
authors.forename: W C
authors.initials: WC
authors.lastname: Zamboni
authors.forename: C F
authors.initials: CF
authors.lastname: Stewart
authors.forename: J
authors.initials: J
authors.lastname: Thompson
authors.forename: V M
authors.initials: VM
authors.lastname: Santana
authors.forename: P J
authors.initials: PJ
authors.lastname: Cheshire
authors.forename: L B
authors.initials: LB
authors.lastname: Richmond
authors.forename: X
authors.initials: X
authors.lastname: Luo
authors.forename: C
authors.initials: C
authors.lastname: Poquette
authors.forename: J A
authors.initials: JA
authors.lastname: Houghton
authors.forename: P J
authors.initials: PJ
authors.lastname: Houghton
mesh_terms: D000310:Adrenal Gland Neoplasms / Q000188:drug therapy; D000818:Animals; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D019046:Bone Marrow Neoplasms / Q000188:drug therapy; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D008808:Mice, Inbred CBA; D009447:Neuroblastoma / Q000188:drug therapy*; D012187:Retroperitoneal Space; D012208:Rhabdomyosarcoma / Q000188:drug therapy*; D059004:Topoisomerase I Inhibitors; D019772:Topotecan / Q000493:pharmacokinetics / Q000494:pharmacology*; D014183:Transplantation, Heterologous
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D059004:Topoisomerase I Inhibitors; D019772:Topotecan