Gene Expression Analysis of Immunomagnetically Enriched Circulating Tumor Cell Fraction in Castration-Resistant Prostate Cancer
Abstract
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(R)) were studied as a source material for high-throughput gene expression analysis using BioMarkTM. Patients and Methods: CTC-enriched samples from 41 CRPC patients previously determined to be CTC positive using the AdnaTest(R) were retrospectively re-analysed for androgen receptor (AR) messenger RNA (mRNA), using the updated AdnaTest(R).
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 BioMarkTM platform in 29 of 41 patients.
Results: The AdnaTest(R) 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 BioMarkTM 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(R) in CTC-enriched samples may help predict patients' survival. These AdnaTest(R) 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 BioMarkTM platform can be used for the simultaneous detection of ARFL and ARV7 and other genes in CTC-enriched samples from CRPC patients.