Abstract
Androgen receptor splice variant V7 (AR-V7) was recently identified as a valuable predictive biomarker in metastatic castrate-resistant prostate cancer. Here, we report a new, sensitive and accurate screen for AR-V7 mRNA expression directly from circulating tumor cells (CTCs): We combined EpCAM-based immunomagnetic CTC isolation using the IsoFlux microfluidic platform with droplet digital polymerase chain reaction (ddPCR) to analyze total AR and AR-V7 expression from prostate cancer patients CTCs. We demonstrate that AR-V7 is reliably detectable in enriched CTC samples with as little as five CTCs, even considering tumor heterogeneity, and confirm detection of AR-V7 in CTC samples from advanced prostate cancer (PCa) patients with AR-V7 detection limited to castrate resistant disease status in our sample set. Sensitive molecular analyses of circulating tumor cells (CTCs) or circulating tumor nucleic acids present exciting strategies to detect biomarkers, such as AR-V7 from non-invasive blood samples, so-called blood biopsies.
Highlights
The insight that cancers, even of the same type, show strong inter- and intra-patient heterogeneity has emerged in recent years
For instance the detection of v-Raf murine sarcoma viral oncogene homolog B (BRAF) V600E mutation is decisive for melanoma treatment options that involve targeted BRAF kinase inhibitors, and V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations in colorectal cancer patients predict resistance to anti-epithelial growth factor receptor (EGFR) monoclonal antibody based therapy [4,5]
We developed a specific and sensitive droplet digital polymerase chain reaction (ddPCR)-based assay to determine Androgen receptor splice variant V7 (AR-V7) expression in prostate cancer (PCa) circulating tumor cells (CTCs) samples that can reliably detect androgen receptor (AR)-V7 expression from CTC positive patient samples
Summary
The insight that cancers, even of the same type, show strong inter- and intra-patient heterogeneity has emerged in recent years. The number of identified actionable biomarkers (biomarkers that determine the best type of therapy) and the generation of novel targeted drugs are currently increasing faster than ever, leading to major changes in personalized therapy and clinical praxis. Some serum proteins, such as the prostate specific antigen (PSA) in prostate cancer (PCa) and carcinoembryonic antigen (CEA) in colorectal cancer, are well established biomarkers and clinically widely used, their correlation with other disease progression parameters is not always ideal [2,3]. For instance the detection of v-Raf murine sarcoma viral oncogene homolog B (BRAF) V600E mutation is decisive for melanoma treatment options that involve targeted BRAF kinase inhibitors, and V-Ki-ras Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations in colorectal cancer patients predict resistance to anti-epithelial growth factor receptor (EGFR) monoclonal antibody based therapy (panitumumab and cetuximab) [4,5]
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