Urinary exosomes as a stable source of mRNA for prostate cancer analysis.

Abstract

174 Background: Exosomes are novel lipid bilayer vesicles that are released into biofluids such as urine and carry high integrity RNA from the parent cell which they were derived. Due to their unique stability and the fact that they contain prostate specific mRNA transcripts, we examined their potential as a non-invasive source of mRNA biomarkers for prostate cancer analysis. Methods: Following a Columbia University approved IRB protocol, random urine samples were collected from 163 men who were stratified into 4 groups: biopsy negative (Bx Neg, n=39), biopsy positive (Bx Pos, n=47), post-radical prostatectomy (RP, n=37) and controls (males <35 yrs, n=40). Urine samples were stored at 4°C and 0.8 μm filtration was used to remove whole cells and debris. Urinary exosomal RNA was isolated using our in-house technique. RT-qPCR was used to analyze PSA, PCA3, androgen receptor (AR), survivin, NCOA2, RAD21, transmembrane protease serine 2 (TMPRSS2), ERG and TMPRSS2:ERG fusion at the mRNA level. Results: Mean serum PSA protein level and age were similar in the Bx Neg and Bx Pos groups. Relative quantitation (RQ) of genes standardized to the PSA gene revealed that ERG (P<0.005), PCA3 (P<0.005), TMPRSS2:ERG fusion (P<0.05), TMPRSS2 (P<0.05) and survivin (P<0.005) were significantly increased in the Bx Pos vs. Bx Neg group. TMPRSS2:ERG fusion events occurred in 68% of Bx Pos vs. 44% of Bx Neg patients and were present in only 5% of controls. No patient in the RP group had positive TMPRSS2:ERG detection; this finding was further supported by the loss of TMPRSS2:ERG expression for 4 Bx Pos patients following prostatectomy suggesting specificity of the fusion event to the prostate. Conclusions: This study confirms urinary exosomes as a source of high quality RNA and showed significant differences in the expression of ERG, PCA3, TMPRSS2:ERG genes between the Bx Pos and Bx Neg groups. Our findings are consistent with previous studies based on tissue and post-prostate massage urinary cell analyses. The unique stability and yield of urinary exosomal RNA collected without a prostatic massage will hopefully simplify sample handing, obviate sample variability and patient discomfort inherent to prostate massage, and broaden the role of exosomes in future diagnostic testing.