title: Biochemical correlates of temozolomide sensitivity in pediatric solid tumor xenograft models.
abstract: The antitumor activity of the methylating agent temozolomide has been evaluated against a panel of 17 xenografts derived from pediatric solid tumors. Temozolomide was administered p.o. daily for five consecutive days at a dose level of 66 mg/kg. Courses of treatment were repeated every 21 days for three cycles. Tumor lines were classified as having high, intermediate, or low sensitivity, determined by complete responses, partial responses, or stable disease, respectively. Overall, temozolomide induced complete responses in five lines and partial responses in three additional tumor lines, giving objective regressions in 47% of xenograft lines. Analysis of temozolomide plasma systemic exposure indicated that this dose level was relevant to exposure achieved in patients. Tumors were analyzed by immunoblotting for levels of O6-methylguanine-DNA methyltransferase (MGMT) and two mismatch repair proteins, MLH-1 and MSH-2. Tumors classified as having high or intermediate sensitivity had low or undetectable MGMT and expressed detectable MLH-1 and MSH-2 proteins. Tumors classified as having low sensitivity had either (a) high MGMT or (b) low or undetectable MGMT but were deficient in MLH-1. The relationship between p53 and response to temozolomide was also examined. In vitro temozolomide did not induce p21cip1 in p53-competent NB-1643 neuroblastoma cells. Suppression of p53 function in NB1643 clones through stable expression of a trans dominant negative p53 (NB1643p53TDN) did not confer temozolomide resistance. Similarly, tumor sensitivity to temozolomide did not segregate with p53 genotype or p53 functional status. These results indicate that MGMT is the primary mechanism for temozolomide resistance, but in the absence of MGMT, proficient mismatch repair determines sensitivity to this agent.
authors.affiliation: Department of Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA. david.middlemas@stjude.org
authors.forename: D S
authors.initials: DS
authors.lastname: Middlemas
authors.forename: C F
authors.initials: CF
authors.lastname: Stewart
authors.forename: M N
authors.initials: MN
authors.lastname: Kirstein
authors.forename: C
authors.initials: C
authors.lastname: Poquette
authors.forename: H S
authors.initials: HS
authors.lastname: Friedman
authors.forename: P J
authors.initials: PJ
authors.lastname: Houghton
authors.forename: T P
authors.initials: TP
authors.lastname: Brent
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000493:pharmacokinetics / Q000627:therapeutic use*; D020137:Base Pair Mismatch; D001932:Brain Neoplasms / Q000473:pathology / Q000517:prevention & control; D002352:Carrier Proteins; D002455:Cell Division / Q000187:drug effects; D002648:Child; D004260:DNA Repair; D004268:DNA-Binding Proteins; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics / Q000627:therapeutic use; D005260:Female; D006801:Humans; D051379:Mice; D008808:Mice, Inbred CBA; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009363:Neoplasm Proteins / Q000378:metabolism; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D009447:Neuroblastoma / Q000473:pathology / Q000517:prevention & control; D009687:Nuclear Proteins; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000378:metabolism; D010641:Phenotype; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D012208:Rhabdomyosarcoma / Q000473:pathology / Q000517:prevention & control; D000077204:Temozolomide; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000502:physiology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018906:Antineoplastic Agents, Alkylating; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C501486:MLH1 protein, human; C501485:Mlh1 protein, mouse; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; D003606:Dacarbazine; D019853:O(6)-Methylguanine-DNA Methyltransferase; C497172:MSH2 protein, human; C497173:Msh2 protein, mouse; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; C010243:5-(3-methyl-1-triazeno)imidazole-4-carboxamide; D000077204:Temozolomide