Biomarker screening for the early detection of prostate cancer using an exosomal-enrichment RNA liquid biopsy test.

Abstract

e15553 Background: Prostate cancer is one of the most common cancers in men, with approximately 10% of all new cancer cases and ~5% of all cancer deaths in 2019. The standard test for prostate cancer is the Prostate Serum Antigen (PSA) test. The PSA test suffers from low specificity (20-40%) in patients including ‘grey zone’ levels (4-10 ng/mL); moreover, the PSA test fails to identify patients with high-risk cancers. Previously we developed ExoDx Prostate Intelliscore (EPI), a urine-based exosome prostate cancer test optimized to rule out the need for a biopsy (risk stratification for high-grade prostate cancer). This study utilized a next generation exosome-based test that specifically enriches a subtype of prostate cancer exosomes from urine. Early detection of prostate cancer via a non-invasive method is desirable and the identification of patients with high-risk cancer is critical. Here we describe the development of a prostate-specific urinary exosome test for the identification of patients with prostate cancer. Methods: We have developed a prostate-specific enrichment method to isolate exosomes of prostate origin from urine samples. Using an affinity-based method against surface marker proteins found on prostate cells, we were able to selectively enrich for exosomes shed by the prostate gland with demonstrated specificity. Subsequent analysis of exosomal nucleic acids enables a promising panel of gene expression biomarkers capable of distinguishing patients with prostate cancer from healthy individuals. Results: RNA from prostate cancer enriched exosomes was compared to total exosomes from urine. Enrichment of prostate cancer specific exosomes significantly enhanced the RNA signature compared to total urine exosomes. Conclusions: Prostate cancer tests have recently been developed for RNA signatures in urine. Exosomes provide a source of nucleic acids as they are actively shed continuously from living cells as part of their normal life cycle. The urine exosomes can be used for total RNA transcriptome analysis and are therefore a very rich source of biomarkers for prostate cancer that can be tailored to different clinical indications. An affinity-based enrichment for tissue-specific exosomes allow for better resolution of the gene expression profile from the tissue of interest and reduces the RNA targets from non-relevant processes of the bladder and kidneys. The gene signature identified in this ongoing study could potentially provide a non-invasive molecular means for the early diagnosis of prostate cancer.