BACKGROUND: Molecular characterization of tumors could be a key to therapeutic decision-making with regards to targeted therapies in castration-resistant prostate cancer (CRPC). A convenient solution may be non-invasive liquid biopsy testing of circulating tumor cells (CTCs). For this reason, CTC-enriched samples obtained by immunomagnetic separation (AdnaTest®) were studied as a source material for high-throughput gene expression analysis using BioMark™. PATIENTS AND METHODS: CTC-enriched samples from 41 CRPC patients previously determined to be CTC positive using the AdnaTest® were retrospectively re-analysed for androgen receptor (AR) messenger RNA (mRNA), using the updated AdnaTest®. Blood samples were drawn two times from each patient: at the time of CRPC diagnosis and after the third docetaxel cycle. A gene expression panel of 27 genes related to CRPC therapeutic decision-making, including AR full length (ARFL) and splice variant 7 (ARV7), was retrospectively analyzed on a BioMark™ platform in 29 of 41 patients. RESULTS: The AdnaTest® detected AR mRNA in three-quarters of CTC-positive samples taken at the time of CRPC diagnosis and after the third docetaxel cycle. AR detection was associated with a shorter disease-specific survival (45.0 vs. 20.4 months) at the time of CRPC diagnosis. ARFL expression at the time of CRPC diagnosis, measured on the BioMark™ platform, was associated with a lower decrease of serum level of prostate-specific antigen (sPSA) (p = 0.029), i.e., worse therapy response. ARV7 was found in 38% of the ARFL--positive samples at both analyzed timepoints. CONCLUSION: Detection of AR expression by AdnaTest® in CTC-enriched samples may help predict patients' survival. These AdnaTest® CTC-enriched samples can be used in a high-throughput quantitative polymerase chain reaction (qPCR) analysis of gene expression, provided that the specificity of the assay for each individual gene is properly validated. The BioMark™ platform can be used for the simultaneous detection of ARFL and ARV7 and other genes in CTC-enriched samples from CRPC patients.

Department of Oncology General University Hospital Prague and 1st Faculty of Medicine Charles University Prague U Nemocnice 2 12808 Prague Czech Republic

Department of Urology General University Hospital and 1st Faculty of Medicine Charles University Prague Ke Karlovu 6 12808 Prague Czech Republic

Institute of Laboratory Diagnostics 3rd Faculty of Medicine Charles University Prague Šrobárova 1150 50 100 34 Prague Czech Republic

Institute of Medical Biochemistry and Laboratory Diagnostics General University Hospital and 1st Faculty of Medicine Charles University Prague U Nemocnice 2 12808 Prague Czech Republic

Institute of Medical Biochemistry and Laboratory Diagnostics General University Hospital and 1st Faculty of Medicine Charles University Prague U Nemocnice 2 12808 Prague Czech Republic Laboratory of Immunology and Allergology Karlovo náměstí 32 128 00 Prague Czech Republic

Laboratory of Gene Expression Institute of Biotechnology CAS Průmyslová 595 252 50 Vestec Czech Republic

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