Quantification of p53 protein in tumor cell lines, breast tissue extracts and serum with time-resolved immunofluorometry.

We have developed a highly sensitive time-resolved immunofluorometric procedure for quantifying mutant or wild-type, human or murine, p53 protein. The method uses monoclonal PAb240 or PAb421 antibodies for capture and a polyclonal rabbit antibody for detection. The final immunocomplex is quantified with an alkaline phosphatase substrate which, when hydrolyzed by the enzyme, forms highly fluorescent long-lived complexes with Tb(3+)-EDTA. The detection limit is approximately 1 pg of protein per assay. The assay was applied for the quantification of p53 protein in lysates from 23 cell lines and overproducers of mutant protein were identified. Eight hundred cancer patients sera tested negative for the presence of p53. We have also applied the quantitative immunofluorometric procedure for measuring mutant p53 protein in breast tumor extracts specifically prepared for steroid hormone receptor analysis. Sixty-four out of the 264 extracts (24%) were positive for p53. Significant negative correlations between levels of p53 and steroid hormone receptors were found. The proposed analytical methodology simplifies the assessment of p53 status in tumor extracts, has many advantages over immunohistochemical techniques and is proposed as a method of choice for routine clinical use and other investigations involving p53.