Disruption of p53 function sensitizes breast cancer MCF-7 cells to cisplatin and pentoxifylline.
The possibility that appropriately designed chemotherapy could act selectively against p53-defective tumor cells was explored in MCF-7 human breast cancer cells. These cells were chosen because they have normal p53 function but are representative of a tumor cell type that does not readily undergo p53-dependent apoptosis. Two sublines (MCF-7/E6 and MCF-7/mu-p53) were established in which p53 function was disrupted by transfection with either the human papillomavirus type-16 E6 gene or a dominant-negative mutant p53 gene. p53 function in MCF-7/E6 and MCF-7/mu-p53 cells was defective relative to control cells in that there were no increases in p53 or p21Waf1/Cip1 protein levels and no G1 arrest following exposure to ionizing radiation. Survival assays showed that p53 disruption sensitized MCF-7 cells to cisplatin (CDDP) but not to several other DNA-damaging agents. CDDP sensitization was not limited to MCF-7 cells since p53 disruption in human colon carcinoma RKO cells also enhanced sensitivity to CDDP. Contrary to the other DNA-damaging agents tested, CDDP-induced DNA lesions are repaired extensively by nucleotide excision, and in agreement with a defect in this process, MCF-7/E6 and MCF-7/mu-p53 cells exhibited a reduced ability to repair a CDDP-damaged chloramphenicol acetyltransferase-reporter plasmid transfected into the cells. Therefore, we attributed the increased CDDP sensitivity of MCF-7 cells with disrupted p53 to defects in G1 checkpoint control, nucleotide excision repair, or both. The G2 checkpoint inhibitor pentoxifylline exhibited synergism with CDDP in killing MCF-7/E6 cells but did not affect sensitivity of the control cells. Moreover, pentoxifylline inhibited G2 checkpoint function to a greater extent in MCF-7/E6 than in the parental cells. These results suggested that, in the absence of p53 function, cancer cells are more vulnerable to G2 checkpoint abrogators. Our results show that a combination of CDDP and pentoxifylline is capable of synergistic and preferential killing of p53-defective tumor cells that do not readily undergo apoptosis.
Fan
S
S
Laboratory of Molecular Pharmacology, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA.
Smith
M L
ML
Rivet
D J
DJ
Duba
D
D
Zhan
Q
Q
Kohn
K W
KW
Fornace
A J
AJ
O'Connor
P M
PM
D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002945:Cisplatin / Q000494:pharmacology*; D002999:Clone Cells; D004317:Doxorubicin / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D016193:G1 Phase / Q000187:drug effects / Q000528:radiation effects; D005720:Gamma Rays; D005814:Genes, Viral; D016158:Genes, p53; D006801:Humans; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D009857:Oncogenes; D027383:Papillomaviridae / Q000235:genetics; D010431:Pentoxifylline / Q000494:pharmacology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D005047:Etoposide; D004317:Doxorubicin; D008741:Methyl Methanesulfonate; D002945:Cisplatin; D010431:Pentoxifylline