Dr. J. Nilsson and an international team of investigators reported a new biomarker methodology for prostate cancer (CaP). They explained that prostatic secretions contain two types of microvesicles; prostasomes (150-500nm) are produced by prostatic ductal epithelial cells that are a normal component of seminal fluid and participate in male fertility and exosomes which are specialized nanovesicles (30-100nm) with cup-shaped morphology and are actively secreted by normal and tumor cells.
Exosomes are secreted in increased amounts in a variety of malignant fluids and can be enriched with certain RNA transcripts several hundred times compared to donor cells. Exosomes lack all ribosomal RNA and contains mostly mRNA and microRNAs. This means that exosomes are enriched with to transcripts specific tumor cells that may possibly be below the detection limit in the tumor cells themselves.
The researchers employed RT-PCR to evaluate urine from four groups of CaP patients; before and after prostatic massage in patients with CaP prior to treatment, undergoing androgen deprivation therapy (ADT), with bone metastases, and a subset selected for electron microscopy. Nested PCR was employed to detect transcripts of TMPRSS2:ERG and PCA-3, both mRNA prostate cancer biomarkers. The mRNA transcripts for the fusion gene TMPRSS2:ERG were detected in 2 of 4 patients who had a high Gleason score and PSA levels, but not in 2 low risk tumors. PCA-3 transcripts were detected in all of the patients after mild prostate massage. Neither patients undergoing ADT nor those with bone metastases had detectable PSA mRNA levels or were positive for PCA-3or TMPRSS2:ERG. These findings are attributed to effective response to ADT and impaired/non-functional prostate tissue. Electron microscopy noted exosomes in the urine fractions of patients with a high-grade tumor, confirmed by anti-CD63 gold staining. The larger prostasomes were not present in the urine of CaP patients and exosomes were not present in the urine of patients without CaP. These data suggest that this technique of identifying biomarkers in the urinary exosomes of CaP patients may potentially be developed as a useful clinical test.