Detection of prostate-specific antigen mRNA by reverse transcription polymerase chain reaction and time-resolved fluorometry

We have developed a time-resolved fluorometric hybridization assay for detecting prostate-specific antigen (PSA) mRNA amplified by reverse transcription polymerase chain reaction. During PCR, digoxigenin-11-dUTP is incorporated into the amplified product. An oligonucleotide internal to the primers is used as a specific probe, being biotinylated and captured on streptavidin-coated microtiter wells. Denatured PCR product hybridizes with the probe, and the hybrids are detected with an alkaline phosphatase-labeled antidigoxigenin antibody. We used the phosphate ester of fluorosalicylic acid as the substrate. The fluorosalicylate produced forms a highly fluorescent ternary complex with Tb(3+)-EDTA, which we can measure by time-resolved fluorometry. A signal-to-background ratio of 10 was obtained when 160 PSA cDNA molecules were present in the preamplification sample. Also, mRNA corresponding to one LNCaP cell in the presence of 10(6) PSA-negative cells can be detected (signal-to-background ratio of 3.1). Samples containing 100, 1000, and 50,000 LNCaP cells gave CVs of 12.4%, 4.9%, and 6.8%, respectively (n = 10).