Circumvention and reactivation of the p53 oncogene checkpoint in mouse colon tumors.
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.
Aizu
Wataru
W
Department of Molecular & Cell Biology, 91 North Eagleville Road, University of Connecticut, Storrs, CT 06269-3125, USA.
Belinsky
Glenn S
GS
Flynn
Christopher
C
Noonan
Emily J
EJ
Boes
Colleen C
CC
Godman
Cassandra A
CA
Doshi
Bindi
B
Nambiar
Prashant R
PR
Rosenberg
Daniel W
DW
Giardina
Charles
C
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*
D002273:Carcinogens; D007093:Imidazoles; D010879:Piperazines; D016159:Tumor Suppressor Protein p53; C482205:nutlin 3; D051736:Proto-Oncogene Proteins c-mdm2; D001397:Azoxymethane