An evaluation of the ability of pifithrin-alpha and -beta to inhibit p53 function in two wild-type p53 human tumor cell lines.
The small-molecule compound pifithrin-alpha (PFT-alpha) has been reported to inhibit p53 function and protect against a variety of genotoxic agents. We show here that PFT-alpha is unstable in tissue culture medium and is rapidly converted to its condensation product PFT-beta. Both compounds showed limited solubility with PFT-alpha precipitating out of tissue culture medium at concentrations >30 micromol/L. PFT-alpha and -beta exhibited cytotoxic effects in vitro towards two human wild-type p53-expressing tumor cell lines, A2780 ovarian and HCT116 colon (IC(50) values for both cell lines were 21.3 +/- 8.1 micromol/L for PFT-alpha and 90.3 +/- 15.5 micromol/L for PFT-beta, mean +/- SD, n = 4). There was no evidence of protection by clonogenic assay with either compound in combination with ionizing radiation. Indeed, there was some evidence that PFT-alpha enhanced cytotoxicity, particularly at higher concentrations of PFT-alpha. Neither compound had any effect on p53, p21, or MDM-2 protein expression following ionizing radiation exposure and there was no evidence of any abrogation of p53-dependent, ionizing radiation-induced cell cycle arrest. Similarly, there was no evidence of cellular protection, or of effects on p53-dependent gene transcription, or on translation of MDM-2 or p21 following UV treatment of these human tumor cell lines. In addition, there was no effect on p53 or p21 gene transactivation or p38 phosphorylation after UV irradiation of NIH-3T3 mouse fibroblasts. In conclusion, neither PFT-alpha nor -beta can be regarded as a ubiquitous inhibitor of p53 function, and caution should be exercised in the use of these agents as specific p53 inhibitors.
Walton
Mike I
MI
Cancer Research UK Centre for Cancer Therapeutics, The Institute of Cancer Research, Haddow Laboratories, Sutton Surrey. Mike.Walton@icr.ac.uk
Wilson
Stuart C
SC
Hardcastle
Ian R
IR
Mirza
Amin R
AR
Workman
Paul
P
D000818:Animals; D052160:Benzothiazoles; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D041681:NIH 3T3 Cells; D010051:Ovarian Neoplasms / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D013844:Thiazoles / Q000494:pharmacology*; D014050:Toluene / Q000031:analogs & derivatives* / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors* / Q000378:metabolism
D052160:Benzothiazoles; D013844:Thiazoles; D016159:Tumor Suppressor Protein p53; D014050:Toluene; C121565:pifithrin; D020928:Mitogen-Activated Protein Kinases