Use of urinary microvesicles for noninvasive mRNA expression analysis in patients with prostate cancer.

Abstract

e15033 Background: Microvesicles (including exosomes) are small lipid bilayer vesicles released from all cells into bodily fluids and have been shown to harbor both RNA and DNA from the parent cell from which they were released. Recently, a rapid method to extract high integrity RNA from microvesicles was developed allowing reliable assessment of their mRNA content. This allows us to gain a transcriptional profile of organs such as the prostate without the need for invasive biopsy. Here we use microvesicles to examine the expression pattern of various genes associated with prostate cancer including the fusion marker TMPRSS:ERG previously shown to be expressed in ~50% of all prostate cancer patients. Methods: A voided (without DRE) or catheterized urine sample was collected from patients with known or suspected prostate cancer from Columbia University Medical Center under approved IRB guidelines. Microvesicles were isolated using a rapid in-house filtration based isolation technique. During RNA extraction a DNase step was included to remove contaminating DNA. RNA integrity was assessed using the Agilent Bioanalyzer. Isolated RNA was used to assess the expression of key prostate markers such as PSA, PCA3 and TMPRSS:ERG. Results: RNA with visible rRNA peaks was successfully isolated from all urine samples assessed. Prostate marker transcripts for PSA, PCA3 and TMPRSS:ERG could be readily detected without the need for a DRE. An initial blinded pilot study of 11 patients revealed that 4 patients were shown to express TMPRSS:ERG mRNA and that these patients corresponded to known prostate cancer patients. TMPRSS:ERG was undetectable in controls and patients with benign prostatic hyperplasia or previously removed prostate cancers. Conclusions: The gene expression profile of prostate cancer patients and controls can be elucidated by isolation of microvesicle mRNA in a voided sample without the need for a DRE. This novel diagnostic tool is currently being investigated in a cohort of 100 cancer patients and controls.