Detection of prostate cancer cells circulating in peripheral blood by reverse transcription-PCR for hKLK2

Two of the human tissue kallikrein family, hK2 and hK3 (prostate-specific antigen), are primarily produced by the prostatic epithelium under the regulation of androgens. In this study, we detected prostate cancer cells that expressed hKLK2 or hKLK3 mRNA in the peripheral blood of patients with prostate cancer using reverse transcription-PCR (RT-PCR). We then demonstrated some differences in characteristics, such as differentiation of cancer cells and response to antiandrogen therapy, between hKLK2 and hKLK3 mRNA-expressing prostate cancer cells. Total RNA was isolated from 41 patients with known prostate cancer, 7 patients with benign prostatic hyperplasia, and 20 normal volunteers. By RT-PCR, hKLK2 mRNA was detected in 7 patients (33%), and hKLK3 mRNA was detected in 17 (81%) of 21 stage D prostate cancer patients. In contrast, all patients with benign prostatic hyperplasia and healthy volunteers were negative. From comparison of the background of the patients positive for hKLK2 and/or hKLK3 mRNA, it became evident that the response to antiandrogen therapy and the expression of hKLK2 mRNA were reciprocally correlated, in contrast with the expression of hKLK3 mRNA. Additionally, our study clearly demonstrated that the detection of hKLK2 mRNA in the peripheral blood was useful for screening patients with certain prostate cancers that did not express hK3. We conclude that taking advantage of the difference between hKLK2 mRNA and hKLK3 mRNA expression is clinically useful for following up prostate cancer patients.