Novel Immunoassay Developed for Prostate Cancer

A blood test that uses proximity ligation (PLA) techniques has been applied as an innovative method for diagnosing prostate cancer.

The proximity ligation technique is uniquely specific and effective in the determination of proteins and the method has now been adapted for detecting abnormal levels of nanometer-sized vesicles called prostasomes.

Scientists at the University of Uppsala (Sweden) created monoclonal antibodies to recognize simultaneously proteins on the surface of the prostasomes, and this allowed them to detect elevated levels of prostasomes in the blood of patients with prostate cancer. The assay, called the 4PLA, detects complex target structures such as microvesicles in which the target is first captured via an immobilized antibody and subsequently detected by using four other antibodies with attached DNA strands.

Blood plasma was obtained from two groups of patients with prostate cancer and compared with age-matched controls. In a second group, samples from 59 patients, aged 53-73 years, whose Prostate Secreted Antigen (PSA) test results were between 1.1 ng/mL - 39.1 ng/mL, were compared with 20 age-matched controls with benign results from transrectal ultrasound-guided biopsies, aged 53-75 years, whose PSA test results were between 1.7 ng/mL - 14.8 ng/mL.

The assay successfully detected significantly elevated levels of prostasomes in blood samples from patients with prostate cancer before radical prostatectomy, as compared with controls and men with benign biopsy results. The medians for prostasome levels in blood plasma of patients with prostate cancer were from 2.5 to 7-fold higher compared with control samples in two independent studies. The assay also distinguished patients with high and medium prostatectomy Gleason scores (8/9 and 7, respectively) from those with low score, equal to or less than 6, thus reflecting disease aggressiveness. The approach that enables detection of prostasomes in peripheral blood may be useful for early diagnosis and assessment of prognosis in organ-confined prostate cancer.

Proximity ligation technology used in this study is commercialized by Olink Bioscience (Uppsala, Sweden). In the limited patient material examined in the study, blood levels of prostasomes seem to correlate more closely with the severity of the disease than do PSA levels. The authors of the study are hopeful that this type of biomarker will prove valuable not only for prostate cancer but also in several other common tumor types. The study was published on May 13, 2011, in the Proceedings of the National Academy of Sciences of the Unites States of America (PNAS).

Related Links:
University of Uppsala
Olink Bioscience