Interlaboratory evaluation of quality control methods for circulating cell-free DNA extraction.

Analysis of circulating cell-free DNA (ccfDNA) isolated from liquid biopsies is rapidly being implemented into clinical practice. However, diagnostic accuracy is significantly impacted by sample quality and standardised approaches for assessing the quality of ccfDNA are not yet established. In this study we evaluated the application of nucleic acid "spike-in" control materials to aid quality control (QC) and standardisation of cfDNA isolation for use in in vitro diagnostic assays. We describe an approach for the design and characterisation of in-process QC materials, illustrating it with a spike-in material containing an exogenous Arabidopsis sequence and DNA fragments approximating to ccfDNA and genomic DNA lengths. Protocols for inclusion of the spike-in material in plasma ccfDNA extraction and quantification of its recovery by digital PCR (dPCR) were assessed for their suitability for process QC in an inter-laboratory study between five expert laboratories, using a range of blood collection devices and ccfDNA extraction methods. The results successfully demonstrated that spiking plasmid-derived material into plasma did not deleteriously interfere with endogenous ccfDNA recovery. The approach performed consistently across a range of commonly-used extraction protocols and was able to highlight differences in efficiency and variability between the methods, with the dPCR quantification assay performing with good repeatability (generally CV <5%). We conclude that initial findings demonstrate that this approach appears "fit for purpose" and spike-in recovery can be combined with other extraction QC metrics for monitoring the performance of a process over time, or in the context of external quality assessment.

Preanalytical robustness of blood collection tubes with RNA stabilizers.

Background Efficient blood stabilization is essential to obtaining reliable and comparable RNA analysis data in preclinical operations. PAXgene (Qiagen, Becton Dickinson) and Tempus (Applied Biosystems, Life Technologies) blood collection tubes with RNA stabilizers both avoid preanalytical degradation of mRNA by endogenous nucleases and modifications in specific mRNA concentrations by unintentional up- or down-regulation of gene expression. Methods Sixteen different preanalytical conditions were tested in PAXgene and Tempus blood samples from seven donors: different mixing after collection, different fill volumes and different 24-h transport temperature conditions after collection. RNA was extracted by column-based methods. The quality of the extracted RNA was assessed by spectrophotometric quantification, A260/A280 purity ratio, RNA Integrity Number (Agilent Bioanalyzer), miRNA quantative real time polymerase chain reaction (qRT-PCR) on two target miRNAs (RNU-24 and miR-16), mRNA quality index by qRT-PCR on the 3' and 5' region of the GAPDH gene, and the PBMC preanalytical score, based on the relative expression levels of the IL8 and EDEM3 coding genes. Results When PAXgene RNA and Tempus blood collection tubes were used following the manufacturers' instructions, there was no statistically or technically significant difference in the output RNA quality attributes. However, the integrity of the RNA extracted from Tempus collection tubes was more sensitive to fill volumes and effective inversion, than to storage temperature, while the integrity of RNA extracted from PAXgene collection tubes was more sensitive to effective inversion and storage temperature than to fill volumes. Conclusions Blood collection tubes with different RNA stabilizers present different robustness to common preanalytical variations.

Cold Ischemia Score: An mRNA Assay for the Detection of Extended Cold Ischemia in Formalin-Fixed, Paraffin-Embedded Tissue.

Although there are thousands of formalin-fixed paraffin-embedded (FFPE) tissue blocks potentially available for scientific research, many are of questionable quality, partly due to unknown preanalytical variables. We analyzed FFPE tissue biospecimens as part of the National Cancer Institute (NCI) Biospecimen Preanalytical Variables program to identify mRNA markers denoting cold ischemic time. The mRNA was extracted from colon, kidney, and ovary cancer FFPE blocks (40 patients, 10-12 hr fixation time) with 1, 2, 3, and 12 hr cold ischemic times, then analyzed using qRT-PCR for 23 genes selected following a literature search. No genes tested could determine short ischemic times (1-3 hr). However, a combination of three unstable genes normalized to a more stable gene could generate a "Cold Ischemia Score" that could distinguish 1 to 3 hr cold ischemia from 12 hr cold ischemia with 62% sensitivity and 84% specificity.

Small Nucleolar RNA Score: An Assay to Detect Formalin-Overfixed Tissue.

Although there are millions of formalin-fixed paraffin-embedded (FFPE) tissue blocks potentially available for scientific research, many are of questionable quality, partly due to unknown fixation conditions. We analyzed FFPE tissue biospecimens as part of the NCI Biospecimen Preanalytical Variables (BPV) program to identify microRNA (miRNA) markers for fixation time. miRNA was extracted from kidney and ovary tumor FFPE blocks (19 patients, cold ischemia ≤2 hours) with 6, 12, 24, and 72 hours fixation times, then analyzed using the WaferGen SmartChip platform (miRNA chip with 1036 miRNA targets). For fixation time, principal component analysis of miRNA chip expression data separated 72 hours fixed samples from 6 to 24 hours fixed samples. A set of small nuclear RNA (snRNA) targets was identified that best determines fixation time and was validated using a second independent cohort of seven different tissue types. A customized assay was then developed, based on a set of 24 miRNA and snRNA targets, and a simple "snoRNA score" defined. This score detects FFPE tissue samples with fixation for 72 hours or more, with 79% sensitivity and 80% specificity. It can therefore be used to assess the fitness-for-purpose of FFPE samples for DNA or RNA-based research or clinical assays, which are known to be of limited robustness to formalin overfixation.

Method Validation for Extraction of Nucleic Acids from Peripheral Whole Blood.

BACKGROUND: This article is the fifth in a series of publications providing formal method validation for biospecimen processing. We report the optimization and validation of methodology to obtain nucleic acids of sufficient quantity and quality from blood. METHODS: DNA was extracted using the Chemagic DNA Blood Kit on an MSM I. Extraction was optimized in terms of blood volume, elution buffer volume, and lysis conditions. The optimal protocol was validated for reproducibility, robustness (delay to buffy coat extraction, blood vs. buffy coat, and use of a magnetic rack), and performance (yield, purity, and concentration). RNA was extracted using a PAXgene Blood miRNA kit with a QiaCube. The protocol was validated for reproducibility, robustness (elution buffer, delay, and temperature before extraction), and performance (yield, purity, integrity, and miRNA content). Two platforms (QiaCube, Biorobot Universal) were further compared. RESULTS: For DNA extraction, a 4 mL blood sample, manual lysis, and 300 µL elution buffer were found to be reproducible (CV <10% for DNA yield and A260 nm/A280 nm ratio) and robust (buffy coat vs. whole blood; immediate processing of buffy coat after lysis vs. storage for 1 week at 2-8°C; and magnetic rack use). There was no difference between automated and manual lysis. RNA extracted with the PAXgene Blood miRNA kit on a QiaCube gave high yields and optimal reproducibility (low CV for RNA yield and integrity) with BR5 elution buffer (vs. water and TE). PAXgene tubes could be stored for up to 2 weeks at 2-8°C. The Biorobot Universal System gave similar mean RNA yields with Qiacube and slightly lower but acceptable purity. CONCLUSIONS: We validated automated isolation of DNA with a Chemagic DNA Blood Kit on a magnetic bead-based MSM I, and of RNA with a PAXgene Blood miRNA kit on a silica membrane-based QiaCube or Biorobot (for low and high throughput, respectively).