Exosomal proteins as prostate cancer biomarkers in urine: From mass spectrometry discovery to immunoassay-based validation.
Exosomes have recently appeared as a novel source of non-invasive cancer biomarkers since tumor-specific molecules can be found in exosomes isolated from biological fluids. We have previously analyzed the proteome of urinary exosomes by mass spectrometry, and identified proteins differentially expressed in prostate cancer patients compared to healthy males. Since mass spectrometry is so far not commonly used in clinical laboratories, we have here investigated whether antibody-based methods such as Western blot or ELISA can be used to validate the use of the identified proteins as prostate cancer biomarkers. Western blot experiments designed to detect flotillin 2, TMEM256, Rab3B and LAMTOR1 showed that the level of these proteins was higher in urinary exosomes from prostate cancer patients compared to healthy males. Furthermore, a receiver operating characteristic curve of flotillin 2 in samples from 16 controls and 16 patients showed an area under the curve of 0.91, and 88% sensitivity at a threshold set to give 94% specificity. In addition, ELISA-based detection of flotillin 2 and PARK7 showed that the combination of these proteins was able to distinguish prostate cancer patients and healthy controls with 68% sensitivity and 93% specificity. Several promising biomarkers identified by mass spectrometry could not be evaluated by Western blot or ELISA due to their low exosomal amount and/or lack of good antibodies. In conclusion, our results show that several urinary exosomal proteins identified as prostate cancer biomarkers by mass spectrometry have a high diagnostic value also when analyzed by immunology-based methods, thus bringing these biomarkers closer to a potential clinical use.
Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital-The Norwegian Radium Hospital, 0379 Oslo, Norway; Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0379 Oslo, Norway.
Ling
L
Wang
Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital-The Norwegian Radium Hospital, 0379 Oslo, Norway; Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0379 Oslo, Norway.
Tore
T
Skotland
Department of Urology, Oslo University Hospital, 0586 Oslo, Norway.
Viktor
V
Berge
Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital-The Norwegian Radium Hospital, 0379 Oslo, Norway; Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0379 Oslo, Norway; Department of Biosciences, University of Oslo, 0316 Oslo, Norway.
Kirsten
K
Sandvig
Department of Molecular Cell Biology, Institute for Cancer Research, Oslo University Hospital-The Norwegian Radium Hospital, 0379 Oslo, Norway; Centre for Cancer Biomedicine, Faculty of Medicine, University of Oslo, 0379 Oslo, Norway. Electronic address: Alicia.Martinez.Llorente@rr-research.no.
Alicia
A
Llorente
D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D055354:Exosomes / Q000378:metabolism*; D006801:Humans; D007118:Immunoassay; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000378:metabolism; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D020692:rab3 GTP-Binding Proteins / Q000378:metabolism
D014408:Biomarkers, Tumor; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C544374:LAMTOR1 protein, human; D008565:Membrane Proteins; C578535:TMEM26 protein, human; C106354:flotillins; C492131:RAB3B protein, human; D020692:rab3 GTP-Binding Proteins
Diagnostics; Exosomes; Extracellular vesicles; Immunology-based assays; Noninvasive biomarkers; Prostate cancer; Urine