Rapid and sensitive detection of hepatitis B virus 1762T/1764A double mutation from hepatocellular carcinomas using LNA-mediated PCR clamping and hybridization probes

Locked Nucleic Acid Probes (LNA) for Enhanced Detection of Low-Level, Clinically Significant Mutations

The detection of clinically significant somatic mutations present at low level in a tissue sample represents a challenge in any laboratory. While several high sensitivity methods are described, the incorporation of these new techniques in a clinical lab may be difficult if the technology is not readily available or requires major changes in the workflow of the laboratory. Techniques that are robust and easily adapted to existing laboratory protocols are highly advantageous. In this chapter we describe the use of locked nucleic acid (LNA) probes to modify existing polymerase chain reaction (PCR)-based protocols which can then be sequenced by Sanger sequencing. LNA probes are used to enhance the sensitivity of Sanger sequencing to mutation frequencies below 1 %. The method is robust and is easily incorporated for assessment of any sample with low tumor content or low mutant allele burden.

Differential methylation of the promoter and first exon of the RASSF1A gene in hepatocarcinogenesis

AIM

Aberrant methylation of the promoter, P2, and the first exon, E1, regions of the tumor suppressor gene RASSF1A, have been associated with hepatocellular carcinoma (HCC), albeit with poor specificity. This study analyzed the methylation profiles of P1, P2 and E1 regions of the gene to identify the region of which methylation most specifically corresponds to HCC and to evaluate the potential of this methylated region as a biomarker in urine for HCC screening.

METHODS

Bisulfite DNA sequencing and quantitative methylation-specific polymerase chain reaction assays were performed to compare methylation of the 56 CpG sites in regions P1, P2 and E1 in DNA isolated from normal, hepatitic, cirrhotic, adjacent non-HCC, and HCC liver tissue and urine samples for the characterization of hypermethylation of the RASSF1A gene as a biomarker for HCC screening.

RESULTS

In tissue, comparing HCC (n = 120) with cirrhosis and hepatitis together (n = 70), methylation of P1 had an area under the receiver operating characteristics curve (AUROC) of 0.90, whereas methylation of E1 and P2 had AUROC of 0.84 and 0.72, respectively. At 90% sensitivity, specificity for P1 methylation was 72.9% versus 38.6% for E1 and 27.1% for P2. Methylated P1 DNA was detected in urine in association with cirrhosis and HCC. It had a sensitivity of 81.8% for α-fetoprotein negative HCC.

CONCLUSION

Among the three regions analyzed, methylation of P1 is the most specific for HCC and holds great promise as a DNA marker in urine for screening of cirrhosis and HCC.

Precore/basal core promoter mutants quantification throughout phases of hepatitis B virus infection by Simpleprobe

AIM: To investigate precore/basal core promoter (PC/BCP) mutants throughout hepatitis B virus (HBV) infection and to determine their relationship to hepatitis B early antigen (HBeAg) titers.

METHODS: We enrolled 191 patients in various stages of HBV infection at the Huashan Hospital and the Taizhou Municipal Hospital from 2010 to 2012. None of the patients received antiviral therapy. HBV DNA from serum, was quantified by real-time PCR. The HBV genotype was determined by direct sequencing of the S gene. We used the Simpleprobe ultrasensitive quantitative method to detect PC/BCP mutants in each patient. We compared the strain number, percentage, and the changes in PC/BCP mutants in different phases, and analyzed the relationship between PC/BCP mutants and HBeAg by multiple linear regression and logistic regression.

RESULTS: Patients with HBV infection (n = 191) were assigned to groups by phase: Immune tolerance (IT) = 55, Immune clearance (IC) = 67, Low-replicative (LR) = 49, and HBeAg-negative hepatitis (ENH) = 20. Of the patients (male, 112; female, 79) enrolled, 122 were HBeAg-positive and 69 were HBeAg-negative. The median age was 33 years (range: 18-78 years). PC and BCP mutation detection rates were 84.82% (162/191) and 96.86% (185/191), respectively. In five HBeAg-negative cases, we detected double mutation G1896A/G1899A. The logarithm value of PC mutant quantities (log₁₀ PC) significantly differed in IT, IC, and LR phases, as well as in the ENH phase (F = 49.350, P < 0.001). The logarithm value of BCP mutant quantities (log₁₀ BCP) also differed during the four phases (F = 25.530, P < 0.001). Log₁₀ PC and log₁₀ BCP values were high in the IT and IC phases, decreased in the LR phase, and increased in the ENH phase, although the absolute value at this point remained lower than that in the IT and IC phases. PC mutant quantity per total viral load (PC%) and BCP mutant quantity per total viral load (BCP%) differed between phases (F = 20.040, P < 0.001; F = 10.830, P < 0.001), with PC% and BCP% gradually increasing in successive phases. HBeAg titers negatively correlated with PC% (Spearman’s rho = -0.354, P < 0.001) and BCP% (Spearman’s rho = -0.395, P < 0.001). The negative correlation between PC% and HBeAg status was significant (B = -5.281, P = 0.001), but there was no such correlation between BCP% and HBeAg status (B = -0.523, P = 0.552).

CONCLUSION: PC/BCP mutants become predominant in a dynamic and continuous process. Log₁₀ PC, log₁₀ BCP, PC% and BCP% might be combined to evaluate disease progression. PC% determines HBeAg status.

Temperature- and flow-enhanced detection specificity of mutated DNA against the wild type with reporter microspheres

Detection of mutated (MT) deoxyribonucleic acid (DNA) amongst the wild type (WT) requires the probe DNA (pDNA) that is complementary to the MT to discriminate the WT by one or two nucleotide mismatches. Traditionally this is achieved by raising the temperature to above the melting temperature (Tm) of the WT (TWT) but below that of the MT (TMT). However, a raised temperature is also accompanied by a weakened binding of the MT to the pDNA which can reduce the detection sensitivity. In this study, we investigated flow as a way to enhance MT detection specificity at a lower temperature. Gold-coated glass (GCG) slides immobilized with pDNA complementary to the target MT were placed at the center of the flow cell. The detection was done by flowing MT or WT at various concentrations followed by flowing 10(5) ml(-1) fluorescent reporter microspheres (FRMs) that were 6 μm in size and coated with reporter DNA complementary to the MT or WT but different from the pDNA at various flow rates and temperatures. The detection of MT or WT was characterized by counting the FRMs captured on the GCG. Hepatitis B virus 1762/1764 double mutation (HBV DM) was the model MT and the TMT and TWT were 47 °C and 22 °C, respectively. It was shown that at room temperature, flow initially increased the binding of both the MT and WT at lower flow rates but decreased the binding at flow rates ≥4 ml min(-1) due to the increase in the flow-induced impingement force on the FRMs to overcome the binding of the MT and the WT to the GCG at higher flow rates. At ≥30 °C the decrease in binding of the WT with an increasing flow rate was more than that of the MT because 30 °C was above the TWT but still well below the TMT. As a result, the detection of MT at 30 °C with a flow rate of 4 ml min(-1) was more specific than at 35 °C without flow. These results indicate that flow can diminish WT binding at a lower temperature than without flow and allow MT detection to occur at a lower temperature with high specificity.

Detection of hypermethylated vimentin in urine of patients with colorectal cancer

We demonstrated previously that urine contains low-molecular-weight (LMW) (<300 bp), circulation-derived DNA that can be used to detect cancer-specific mutations if a tumor is present. The goal of this study was to develop an assay to detect the colorectal cancer (CRC)-associated, circulation-derived, epigenetic DNA marker hypermethylated vimentin gene (mVIM) in the urine of patients with CRC. An artificial 18-nucleotide DNA sequence was tagged at the 5' end of the primers of the first PCR cycle to increase the amplicon size, which was then integrated into the primers of the second PCR cycle. A quantitative MethyLight PCR-based assay targeting a 39-nucleotide template was developed and used to quantify mVIM in CRC tissues and matched urine samples. mVIM was detected in 75% of LMW urine DNA samples from patients with CRC (n = 20) and in 10% of urine samples of control subjects with no known neoplasia (n = 20); 12 of 17 LMW urine DNA samples (71%) but only 2 of 17 high-molecular-weight urine DNA samples (12%) from patients with mVIM-positive tissues contained detectable mVIM, suggesting that the mVIM detected in LMW urine DNA is derived from the circulation. The detection of mVIM in urine was significantly associated with CRC compared with controls (P < 0.0001, by Fisher's exact test). A potential urine test for CRC screening using epigenetic markers is discussed.

PCR enrichment techniques to identify the diet of predators

The increasing sensitivity of PCR has meant that in the last two decades PCR has emerged as a major tool in diet studies, enabling us to refine our understanding of trophic links and to elucidate the diets of predators whose prey is as yet uncharacterized. The achievements and methods of PCR-based diet studies have been reviewed several times, but here we review an important development in the field: the use of PCR enrichment techniques to promote the amplification of prey DNA over that of the predator. We first discuss the success of using group-specific primers either in parallel single reactions or in multiplex reactions. We then concentrate on the more recent use of PCR enrichment techniques such as restriction enzyme digests, peptide nucleic acid clamping, DNA blocking and laser capture microdissection. We also survey the vast literature on enrichment techniques in clinical biology, to ascertain the pitfalls of enrichment techniques and what refinements have yielded some highly sensitive methods. We find that while there are several new approaches to enrichment, peptide nucleic acid clamping and DNA blocking are generally sufficient techniques for the characterization of diets of predators and highlight the most important considerations of the approach.

A locked nucleic acid clamp-mediated PCR assay for detection of a p53 codon 249 hotspot mutation in urine

Hepatocellular carcinoma (HCC) has a 5-year survival rate of <10% because it is difficult to diagnose early. Mutations in the TP53 gene are associated with approximately 50% of human cancers. A hotspot mutation, a G:C to T:A transversion at codon 249 (249T), may be a potential DNA marker for HCC screening because of its exclusive presence in HCC and its detection in the circulation of some patients with HCC. A locked nucleic acid clamp-mediated PCR assay, followed by melting curve analysis (using the SimpleProbe), was developed to detect the TP53 249T mutation. In this assay, the locked nucleic acid clamp suppressed 10(7) copies of wild-type templates and permitted detection of 249T-mutated template, with a sensitivity of 0.1% (1:1000) of the mutant/wild-type ratio, assessed by a reconstituted standard within 2 hours. With an amplicon size of 41 bp, it detects target DNA sequences in short fragmented DNA templates. The detected mutations were validated by DNA sequencing analysis. We then tested DNA isolated from urine samples of patients with HCC for p53 mutations and identified positive TP53 mutations in 9 of 17 samples. The possibility of using this novel TP53 249T assay to develop a urine or blood test for HCC screening is discussed.

Ultrasensitive quantification of hepatitis B virus A1762T/G1764A mutant by a SimpleProbe PCR using a wild-type-selective PCR blocker and a primer-blocker-probe partial-overlap approach

Hepatitis B virus (HBV) carrying the A1762T/G1764A double mutation in the basal core promoter (BCP) region is associated with HBe antigen seroconversion and increased risk of liver cirrhosis and hepatocellular carcinoma (HCC). Quantification of the mutant viruses may help in predicting the risk of HCC. However, the viral genome tends to have nucleotide polymorphism, which makes it difficult to design hybridization-based assays including real-time PCR. Ultrasensitive quantification of the mutant viruses at the early developmental stage is even more challenging, as the mutant is masked by excessive amounts of the wild-type (WT) viruses. In this study, we developed a selective inhibitory PCR (siPCR) using a locked nucleic acid-based PCR blocker to selectively inhibit the amplification of the WT viral DNA but not the mutant DNA. At the end of siPCR, the proportion of the mutant could be increased by about 10,000-fold, making the mutant more readily detectable by downstream applications such as real-time PCR and DNA sequencing. We also describe a primer-probe partial overlap approach which significantly simplified the melting curve patterns and minimized the influence of viral genome polymorphism on assay accuracy. Analysis of 62 patient samples showed a complete match of the melting curve patterns with the sequencing results. More than 97% of HBV BCP sequences in the GenBank database can be correctly identified by the melting curve analysis. The combination of siPCR and the SimpleProbe real-time PCR enabled mutant quantification in the presence of a 100,000-fold excess of the WT DNA.

Mixed Theileria infections in free-ranging buffalo herds: implications for diagnosing Theileria parva infections in Cape buffalo (Syncerus caffer)

Buffalo-adapted Theileria parva causes Corridor disease in cattle. Strict control measures therefore apply to the movement of buffalo in South Africa and include mandatory testing of buffalo for the presence of T. parva. The official test is a real-time hybridization PCR assay that amplifies the V4 hypervariable region of the 18S rRNA gene of T. parva, T. sp. (buffalo) and T. sp. (bougasvlei). The effect that mixed T. parva and T. sp. (buffalo)-like infections have on accurate T. parva diagnosis was investigated in this study. In vitro mixed infection simulations indicated PCR signal suppression at 100 to 1000-fold T. sp. (buffalo) excess at low T. parva parasitaemia. Suppression of PCR signal was found in field buffalo with mixed infections. The T. parva-positive status of these cases was confirmed by selective suppression of T. sp. (buffalo) amplification using a locked nucleic acid clamp and independent assays based on the p67, p104 and Tpr genes. The incidence of mixed infections in the Corridor disease endemic region of South Africa is significant, while the prevalence in buffalo outside the endemic area is currently low. A predicted increase of T. sp. (buffalo)-like infections can affect future diagnoses where mixed infections occur, prompting the need for improvements in current diagnostics.

Molecular methods in the diagnosis and management of chronic hepatitis B

Chronic hepatitis B (CHB) infection remains a major global problem but the recent advances in molecular methods have revolutionized the diagnosis and management of CHB. Hepatitis B virus (HBV) DNA quantitation is the most useful molecular marker for the diagnosis and management of CHB. There is increasing evidence that the clinical outcome and efficacy of antiviral therapy for CHB could vary with the infecting HBV genotype, core promoter and precore mutations. Early identification of drug resistance is imperative in the management of CHB. The molecular methods for HBV DNA quantitation, HBV genotyping, the identification of mutants, genotypic and phenotypic methods for monitoring drug resistance and their utility and limitations for use in the diagnosis and monitoring of CHB are discussed in this article.