title: Circumvention and reactivation of the p53 oncogene checkpoint in mouse colon tumors.
abstract: The p53 tumor suppressor protein is sequence-normal in azoxymethane (AOM)-induced mouse colon tumors, making them a good model for human colon cancers that retain a wild type p53 gene. Cellular localization and co-immunoprecipitation experiments using a cell line derived from an AOM-induced colon tumor (AJ02-NM(0) cells) pointed to constitutively expressed Mdm2 as being an important negative regulator of p53 in these cells. Although the Mdm2 inhibitory protein p19/ARF was expressed in AJ02-NM(0) cells, its level of expression was not sufficient for p53 activation. We tested the response of AJ02-NM(0) cells to the recently developed Mdm2 inhibitor, Nutlin-3. Nutlin-3 was found to activate p53 DNA binding in AJ02-NM(0) cells, to a level comparable to doxorubicin and 5-fluorouracil (5-FU). In addition, Nutlin-3 increased expression of the p53 target genes Bax and PERP to a greater extent than doxorubicin or 5-FU, and triggered a G2/M phase arrest in these cells, compared to a G1 arrest triggered by doxorubicin and 5-FU. The differences in the cellular response may be related to differences in the kinetics of p53 activation and/or its post-translational modification status. In an ex vivo experiment, Nutlin-3 was found to activate p53 target gene expression and apoptosis in AOM-induced tumor tissue, but not in normal adjacent mucosa. Our data indicate that Mdm2 inhibitors may be an effective means of selectively targeting colon cancers that retain a sequence-normal p53 gene while sparing normal tissue and that the AOM model is an appropriate model for the preclinical development of these drugs.
authors.affiliation: Department of Molecular & Cell Biology, 91 North Eagleville Road, University of Connecticut, Storrs, CT 06269-3125, USA.
authors.forename: Wataru
authors.initials: W
authors.lastname: Aizu
authors.forename: Glenn S
authors.initials: GS
authors.lastname: Belinsky
authors.forename: Christopher
authors.initials: C
authors.lastname: Flynn
authors.forename: Emily J
authors.initials: EJ
authors.lastname: Noonan
authors.forename: Colleen C
authors.initials: CC
authors.lastname: Boes
authors.forename: Cassandra A
authors.initials: CA
authors.lastname: Godman
authors.forename: Bindi
authors.initials: B
authors.lastname: Doshi
authors.forename: Prashant R
authors.initials: PR
authors.lastname: Nambiar
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Rosenberg
authors.forename: Charles
authors.initials: C
authors.lastname: Giardina
mesh_terms: D000818:Animals; D017209:Apoptosis; D001397:Azoxymethane; D002273:Carcinogens; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000139:chemically induced / Q000188:drug therapy / Q000378:metabolism*; D016158:Genes, p53; D007093:Imidazoles / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D010879:Piperazines / Q000494:pharmacology*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D002273:Carcinogens; D007093:Imidazoles; D010879:Piperazines; D016159:Tumor Suppressor Protein p53; C482205:nutlin 3; D051736:Proto-Oncogene Proteins c-mdm2; D001397:Azoxymethane