title: Initial testing of topotecan by the pediatric preclinical testing program.
abstract: BACKGROUND
  Topotecan is a small molecule DNA topoisomerase I poison, that has been successful in clinical trials against pediatric solid tumors and leukemias. Topotecan was evaluated against the Pediatric Preclinical Testing Program (PPTP) tumor panels as part of a validation process for these preclinical models.
  
  
  METHODS
  In vivo three measures of antitumor activity were used: (1) an objective response measure modeled after the clinical setting; (2) a treated to control (T/C) tumor volume measure; and (3) a time to event (fourfold increase in tumor volume for solid tumor models, or > or =25% human CD45+ cells in the peripheral blood for acute lymphoblastic leukemia, ALL models) measure based on the median event-free survival (EFS) of treated and control animals for each xenograft.
  
  
  RESULTS
  Topotecan inhibited cell growth in vitro with IC(50) values between 0.71 and 489 nM. Topotecan significantly increased EFS in 32 of 37 (87%) solid tumor xenografts and in all 8 of the ALL xenografts. Seventy-five percent of solid tumors met EFS T/C activity criteria for intermediate (n = 17) or high activity (n = 7). Objective responses were noted in eight solid tumor xenografts (Wilms, rhabdomyosarcoma, Ewing sarcoma, neuroblastoma). Among the six neuroblastomas, three achieved a PR. For the ALL panel, two maintained CRs, three CRs, and two PRs were observed.
  
  
  CONCLUSIONS
  Topotecan demonstrated broad activity in vitro and in vivo against both the solid tumor and ALL panels, with significant tumor growth delay generated in all the panels. These results further demonstrate the validity of the PPTP panel for preclinical testing of new drugs.
authors.affiliation: Children's Cancer Institute Australia for Medical Research, Randwick, NSW, Australia.
authors.forename: Hernan
authors.initials: H
authors.lastname: Carol
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Houghton
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Morton
authors.forename: E Anders
authors.initials: EA
authors.lastname: Kolb
authors.forename: Richard
authors.initials: R
authors.lastname: Gorlick
authors.forename: C Patrick
authors.initials: CP
authors.lastname: Reynolds
authors.forename: Min H
authors.initials: MH
authors.lastname: Kang
authors.forename: John M
authors.initials: JM
authors.lastname: Maris
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Keir
authors.forename: Amy
authors.initials: A
authors.lastname: Watkins
authors.forename: Malcolm A
authors.initials: MA
authors.lastname: Smith
authors.forename: Richard B
authors.initials: RB
authors.lastname: Lock
mesh_terms: D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002648:Child; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D006801:Humans; D008962:Models, Theoretical; D009369:Neoplasms / Q000188:drug therapy*; D019772:Topotecan / Q000008:administration & dosage / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D019772:Topotecan