An exosome-based liquid biopsy assay for the non-invasive early detection of colorectal adenomas and cancers

About This Grant

Project Summary: Colorectal cancer (CRC) is potentially preventable, but still ranks 3rd in diagnosis and 2nd in mortality worldwide: why? CRC screening trials based on fecal immunochemical testing (FIT) showed survival benefits through a stage-shifting effect, reducing stage IV diagnoses but not preventing CRC incidence. FIT sensitivity declines for early-stage CRC and precursor lesions (the advanced adenomas, AAs), emphasizing its impact on mortality rather than incidence. Endoscopy-first approaches have a higher sensitivity, but the contentious results of the NordICC trial demonstrated the numerous challenges of a colonoscopy-first approach, including invasiveness, costs, and patient compliance. In fact, only 54% of the US screening-eligible population has received a colonoscopy in the past 10 years. However, non-invasive tests promote participation. So far, biomarker studies have demonstrated great sensitivity to CRC but not to AAs and early-stage CRC. These investigations operated under the assumption that the same analyte would effectively detect both CRC and AA. However, 1) if both CRC and AAs release the same analyte into the blood, AAs do so in considerably smaller quantities; and 2) adenomas and CRC exist at opposite ends of the adenoma-carcinoma sequence; therefore, they may not yet release the same analytes. Therefore, in this proposal, we advocate for the development of an innovative liquid biopsy, a test that, built separately for AAs and CRC, can assess both AAs and CRC from a single blood draw to optimize patient compliance and resource allocation and enable timely AA detection for cancer prevention. MicroRNAs (miRNAs) are small non-coding RNAs that regulate genes implicated in every human cancer, including CRC and AAs, and may thus be ideal biomarkers. Indeed, circulating cell-free miRNAs (cf-miRNAs) have been shown to have diagnostic potential. Furthermore, the recent discovery that cancer cells actively excrete miRNAs in small extracellular vesicles called exosomes (exo miRNAs) has revolutionized the field, as tumor-derived exosomal cargo enables the identification of cancer-specific molecular markers. To date, our studies have been among only very few to directly compare the clinical significance of cf-miRNAs vs. exo- miRNAs, and our team is unique in proposing a combination of cf- and exo-miRNAs as potentially superior biomarkers. To address the limitations of cf-miRNA biomarkers and to interrogate the potential clinical significance of exo-mRNAs, we completed a systematic and comprehensive biomarker discovery and validation effort in patients with CRC, AAs, and low-risk adenomas. These successes collectively demonstrate our ability to establish a transcriptomic signature for the early detection and prevention of CRC. In this proposal, we will complete three milestone-based specific aims: 1) Refinement and large-scale validation of our assay to establish its performance in a cohort of patients with CRC and AAs. 2) Validate our assay in a cohort of individuals younger than 50 years of age. 3) Evaluate the ability of our transcriptomic signature to detect CRC and AAs at their earliest stages in pre-diagnosis serum specimens and determine lead time before disease presentation.