Detection of circulating prostate cells by reverse transcriptase- polymerase chain reaction of human glandular kallikrein (hK2) and prostate- specific antigen (PSA) messages

Objectives. To investigate the clinical value of human glandular kallikrein (hK2) reverse transcriptase-polymerase chain reaction (RT-PCR) for detection of prostate cells in circulation and to compare the results with those obtained from prostate-specific antigen (PSA) RT-PCR. Methods. We examined peripheral blood (PB) and bone marrow (BM) samples of 13 patients with advanced-stage prostate cancer and 65 patients with clinically localized disease for the presence of circulating prostate cells. An RT-PCR protocol with a two-step amplification cycle and hot-start conditions was used. Results. The limit of detection of the PCR portion is similar for PSA and hK2 (5 to 10 copies of the plasmid containing the cDNA). The RT-PCR limit of detection is one LNCaP cell in 10⁸ peripheral blood mononuclear cells (PMBC) for PSA, and one LNCaP cell in 10⁷ PMBC for hK2. Of the BM samples obtained prior to radical prostatectomy, 71.4% were positive for PSA mRNA and 41.3% were positive for hK2 mRNA. In PB, the PSA positivity was 19% and hK2 positivity 12.7%. In advanced-stage patients, there were 76.9% PSA-positive samples in BM versus 38.5% hK2-positive samples; 46.2% of patients were positive in PB for PSA versus 30.8% for hK2. Conclusions. We have developed a sensitive RT-PCR protocol for detection of hK2 mRNA and evaluated the suitability of hK2 mRNA in comparison with PSA mRNA as an additional marker for detection of prostate cells in circulation. Combining results of these two tests increased the sensitivity of detection.