Simultaneous detection of tumor-derived mutations in DNA and RNA extracted from a single circulating tumor cell based on droplet digital polymerase chain reaction.

Abstract

e15053 Background: Androgen receptor splice variant 7 (AR-V7) is a constitutively activated isoform of AR and has been associated with resistance to AR-targeted therapies and development of metastatic castration-resistant prostate cancer. Confirmation of AR-V7 expression is important step in prostate cancer diagnosis and determining the appropriate drug, however, the detection of AR-V7 with tissues has limitations, such as the clinical challenge to poorly accessible tumor tissues before and after therapy. In addition, KRAS mutations serve as a prognostic biomarker for the administration of appropriate anti-cancer drugs in patients with various cancers, including non-small cell lung cancer (NSCLC). Here, we developed the process for the simultaneous detection of AR-V7 and KRAS mutation in CTCs using isolation with CytoGen’s Smart Biopsy™ System with droplet digital polymerase chain reaction (ddPCR) with high sensitivity and specificity, overcoming the limitations of tissue biopsy. Methods: ddPCR assays were performed to detect the KRAS G12C mutation using CTC gDNA and to evaluate the absolute levels of AR-V7 using CTC mRNA. Analytical validation was performed using NSCLC NCI-H358 and prostate cancer 22Rv1 cells (10 and 5 cells each), which harbor KRAS G12C and AR-V7, respectively, spiked into 5 mL of healthy blood to mimic CTC. CTCs were isolated using CytoGen's Smart Biopsy™ System. Oligo-dT magnetic beads were used to isolate mRNA from CTCs, and gDNA was isolated from the mRNA-depleted CTC lysates using the AllPrep DNA/mRNA Nano Kit. PCR and droplet reading for each assay were performed on the QX200 AutoDG Droplet Digital PCR System. Results: As a result of CTC KRAS G12C detection using the ddPCR™ KRAS G12/G13 Screening Kit, the mutated KRAS gene was successfully detected in as few as 5 NCI-H358 cells. In the results of CTC AR-V7 detection using the custom TaqMan ddPCR assay, transcripts (AR-V7 and HPRT1) were successfully detected even with only 5 22Rv1 cells. These results suggest that CytoGen's Smart Biopsy™ System could be applied to the simultaneous detection of DNA/RNA mutated genes in clinical NSCLC and prostate cancer patients with detection technology requiring high sensitivity and specificity. Conclusions: Accurately detecting multiple genetic mutations in CTCs is a challenging because CTCs are very rare in the blood. In this study, we developed the process to simultaneously extract and detect DNA mutations and RNA splicing variants in CTCs using CytoGen's Smart Biopsy™ System. This process, along with the results from our ongoing clinical trials, could provide information for the diagnosis and appropriate treatment of patients with various cancers, including NSCLC and prostate cancer.