Peptide Nucleic Acid-mediated Polymerase Chain Research Articles

A Highly Sensitive Next-Generation Sequencing-Based Genotyping Platform for EGFR Mutations in Plasma from Non-Small Cell Lung Cancer Patients.

Simple SummaryIn this study, Sel-CapTM, a next-generation sequencing (NGS)-based genotyping platform, showed high sensitivity for detection of epidermal growth factor receptor (EGFR) gene mutations in plasma samples collected from 185 patients with non-small cell lung cancer (NSCLC). In the early-stage NSCLC, Sel-Cap liquid biopsy was able to detect more than half the EGFR mutations, which were detected in tumor tissue (sensitivity: 50% and 78% for Ex19del and L858R respectively, with tumor results as the references), while the conventional NGS could not detect any. Sel-Cap liquid biopsy was particularly sensitive for resistant mutation T790M (sensitivity: 88%). In addition, we conducted a retrospective study to monitor T790M using Sel-Cap in 34 patients who progressed on first-line tyrosine kinase inhibitors (EGFR-TKIs). The study suggested that the first appearance of T790M in plasma, ranging from at treatment baseline to over three years post-EGFR-TKI initiation, may be useful for prediction of disease progression (around 5 months in advance).Sel-CapTM, a digital enrichment next-generation sequencing (NGS)-based cancer panel, was assessed for detection of epidermal growth factor receptor (EGFR) gene mutations in plasma for non-small cell lung cancer (NSCLC), and for application in monitoring EGFR resistance mutation T790M in plasma following first-line EGFR-tyrosine kinase inhibitor (EGFR-TKI) treatment. Using Sel-Cap, we genotyped plasma samples collected from 185 patients for mutations Ex19del, L858R, and T790M, and compared results to those of PNAclampTM tumor biopsy (reference method, a peptide nucleic acid-mediated polymerase chain reaction clamping) and two other NGS liquid biopsies. Over two-thirds of activating mutations (Ex19del and L858R), previously confirmed by PNAclamp, were detected by Sel-Cap, which is 4–5 times more sensitive than NGS liquid biopsy. Sel-Cap showed particularly high sensitivity for T790M (88%) and for early-stage plasma samples. The relationship between initial T790M detection in plasma and progression-free survival (PFS) following first-line EGFR-TKIs was evaluated in 34 patients. Patients with T790M detected at treatment initiation (±3 months) had significantly shorter PFS than patients where T790M was first detected >3 months post treatment initiation (median PFS: 5.9 vs. 26.5 months; p < 0.0001). However, time from T790M detection to disease progression was not significantly different between the two groups (median around 5 months). In conclusion, Sel-Cap is a highly sensitive platform for EGFR mutations in plasma, and the timing of the first appearance of T790M in plasma, determined via highly sensitive liquid biopsies, may be useful for prediction of disease progression of NSCLC, around 5 months in advance.

BRAF and NRAS mutations and antitumor immunity in Korean malignant melanomas and their prognostic relevance: Gene set enrichment analysis and CIBERSORT analysis

Cutaneous malignant melanomas (CMMs) are rare but are the cause of the highest skin cancer-related mortality in Korea. Very few studies have investigated the associations between KRAS, NRAS, BRAF, and PIK3CA mutations and TICs, as well as their prognostic impact on Korean CMMs. Peptide nucleic acid-mediated polymerase chain reaction clamping and Mutyper and immunohistochemistry were used to detect these mutations in 47 paraffinized CMMs. BRAF and NRAS mutations were detected in 21.3% and 12.8% of CMMs, respectively. No KRAS or PIK3CA mutations were identified. NRAS mutations correlated with low FOXP3 (regulatory T lymphocyte marker) and indoleamine 2,3-dioxygenase (IDO) (activated dendritic cell marker) TICs in CMMs, which is consistent with the negative correlation of regulatory T cells with NRAS mutations in TCGA data, while BRAF mutations were not associated with any TICs. In gene set enrichment analysis, BRAF and NRAS mutations were enriched in decreased CD8 (suppressor/cytotoxic T lymphocyte marker) T cell-linked and increased CD4 (helper/inducer T lymphocyte marker) T cell-linked gene signatures, respectively, confirming the trend in our cohort of associations only with NRAS. BRAF or NRAS mutations alone did not affect any prognosis. In the subgroup analyses, BRAF mutations, as well as high CD4, CD8, FOXP3, and IDO TICs, caused worse overall survival in NRAS-mutated melanoma. No correlation of CD163 (monocyte–macrophage-specific marker) was detected.We found that approximately one-third of our cohort had BRAF and NRAS mutations, none had KRAS or PIK3CA mutations, and most displayed decreased anti-tumor immunity. These findings may warrant further study on combined immunotherapeutic and molecular targeted therapy in Korean CMMs. Subgroup analyses according to TICs and BRAF/NRAS mutations may help to identify high-risk patients with worse prognoses.

Detection of PIK3CA Mutations in Plasma DNA of Colorectal Cancer Patients by an Ultra-Sensitive PNA-Mediated PCR.

Mutant Phosphatidylinositol-4, 5-bisphosphate 3-kinase, catalytic subunit alpha (PIK3CA) has been shown to be associated with the occurrence, development and prognosis in colorectal cancer (CRC). However, its detection has been limited because of complicated procedures and the low sensitivity of the present approaches. We established an ultra-sensitive peptide nucleic acid-mediated polymerase chain reaction (PNA-PCR) assay to detect PIK3CA gene mutation in exon 9 and exon 20 with cell-free DNA (cfDNA). Using this technology, we detected the mutation status of PIK3CA in 128 colorectal cancer patients. 6 CRC patients receiving targeted therapy were chosen at random to undergo continuous PIK3CA mutation detection. The results showed that the sensitivity of PNA-PCR clamping method was 0.1% for the exon 9 and 0.2% for the exon 20 variant alleles. When the PIK3CA mutation status was determined by PNA-PCR plus sequencing, 38.3% (49/128) of CRC carried at least one mutation, either E545Kor H1047R. The clinic-pathological parameters of age (p=0.358), gender (p=0.622), disease stage (p=0.353) and disease location (p=0.307) were not associated with the PIK3CA mutation. In the continuous monitoring study, we found that the gene status was associated with the effect of treatment. Furthermore, when the PIK3CA variant was determined by only the PNA-PCR method, there was a good linear relationship between ΔCp values and the proportion of variant DNA. The accuracy of PNA-PCR was 93.75 and 92.27% respectively when the cut-off values of ΔCp at 9.0 and 8.0 were set for determining the E545K and H1047R mutations. A simple, noninvasive, ultra-sensitive PNA-PCR technology was developed and was especially suitable for the dynamic detection of PIK3CA variants using cfDNA.

Mutations of the Epidermal Growth Factor Receptor Gene in Triple-Negative Breast Cancer.

PurposeEpidermal growth factor receptor (EGFR) is considered a potential therapeutic target for anti-EGFR therapy in triple-negative breast cancer (TNBC). However, the frequency of EGFR gene mutation in TNBC is low and varies with ethnicity. This study aimed to investigate the incidence of EGFR gene mutation in TNBC.MethodsEGFR protein expression was evaluated by immunohistochemistry in tissue microarrays of 493 TNBC cases using four different primary antibodies, which included mutation-specific antibodies. For cases with an immunoreactivity level ≥1+, we performed pyrosequencing analysis for EGFR gene mutation. A case was considered mutation-positive when its mutation frequency minus its limit of detection (LOD) was >10%. Cases with mutation frequency higher than LOD were assessed for EGFR gene mutation status using the Cobas assay and by peptide nucleic acid-mediated polymerase chain reaction (PNA-clamping).ResultsAmong 493 TNBCs, 148 (30.0%) exhibited staining ≥1+ for EGFR, including 78 with 1+, 49 with 2+, and 21 with 3+. Positive EGFR expression (≥2+) was significantly associated with lymphovascular invasion (p=0.010), but not with overall survival (p=0.444) or disease-free survival (p=0.388). None of the 493 TNBCs harbored an EGFR gene mutation. Among 148 cases with an EGFR staining result ≥1+, five (3.4%) showed mutation frequencies (4.4%–10.9%) higher than LOD (2.6%–4.3%) in exons 19 (L747_P753>Q) or 21 (L858R and L861Q) as determined by pyrosequencing. However, Cobas and PNA-clamping failed to detect the presence of EGFR gene mutation in these five cases.ConclusionNo activating mutation of EGFR gene of clinical significance was observed in 148 TNBC cases using three commercially available methods. Thus, EGFR gene mutation appears to be an extremely rare event in patients with TNBC.

Low incidence of KRAS, BRAF, and PIK3CA mutations in adenocarcinomas of the ampulla of Vater and their prognostic value

Ampullary adenocarcinomas (A-ACs) are rare malignancies with considerable importance because of their high curable resection rate and improved survival rate among periampullary cancers. The RAS-RAF-MAPK pathway is involved in the development of A-ACs and is a potential therapeutic target. However, molecular profiles of A-ACs and their prognostic impact are poorly understood. Peptide nucleic acid-mediated polymerase chain reaction clamping and Mutyper were used to detect KRAS, BRAF, and PIK3CA mutations in 62 paraffinized samples of A-ACs. Of 62 A-ACs, 30.6% had KRAS mutations, but no BRAF mutations and low frequency (1.6%) of PIK3CA mutation were detected. KRAS mutation was correlated with poor tumor differentiation and was a predictor of shorter recurrence-free survival period in overall A-ACs, whereas the prognosis according to the histologic subtypes was not affected by KRAS mutation. Lymph node metastasis was an independent prognostic factor of poor overall survival. Intestinal- and pancreatobiliary-type A-ACs had similar prognosis. Intestinal- and pancreatobiliary-type A-ACs had different prognostic factors; tumor differentiation and lymph node metastasis strongly predicted overall survival and recurrence-free survival in pancreatobiliary-type tumors, respectively, whereas no independent prognostic factors were demonstrated for intestinal-type tumors. Low incidence of KRAS mutations and their strong prognostic value in A-ACs may suggest the potential of survival benefit depending on the epidermal growth factor receptor-targeted therapy. Much lower frequencies of BRAF and PIK3CA mutations may suggest that they do not play a major role in the tumorigenesis of A-ACs. Different therapeutic protocols should be considered for treating pancreatobiliary- and intestinal-type A-ACs.

ABO chimerism with a minor allele detected by the peptide nucleic acid-mediated polymerase chain reaction clamping method.

Discrepancy of results of ABO groups between red cell testing and serum testing is a significant issue in transfusion medicine1. One of its reported causes is blood chimerism, which shows mixed-field agglutination. However, mixed-field agglutination can be seen in various situations, including ABO-incompatible stem cell transplantation, recent transfusions of type-O red blood cells in a non-O recipient, and rare ABO subgroups such as B3 and chimera. Several molecular approaches have been employed to identify chimerism, namely ABO genotyping, human leucocyte antigen typing and DNA short tandem repeat assays2. These methods can typically detect three or more alleles of a chimera. However, some chimeras with a minor allele population might be overlooked because of preferential amplification of the major allele during ordinary polymerase chain reaction (PCR) analysis. We report a case of blood chimerism in which B red cells accounted for less than 1% of the whole population. The B allele in peripheral blood mononuclear cells could not be identified by direct sequencing of ordinary PCR product involving exons 6 and 7 of the ABO gene, but was revealed using peptide nucleic acid (PNA)-mediated PCR clamping.

KRAS Mutation Detection in Non-small Cell Lung Cancer Using a Peptide Nucleic Acid-Mediated Polymerase Chain Reaction Clamping Method and Comparative Validation with Next-Generation Sequencing.

BackgroundKRAS is one of commonly mutated genetic "drivers" in non-small cell lung cancers (NSCLCs). Recent studies indicate that patients with KRAS-mutated tumors do not benefit from adjuvant chemotherapy, so there is now a focus on targeting KRAS-mutated NSCLCs. A feasible mutation detection method is required in order to accurately test for KRAS status.MethodsWe compared direct Sanger sequencing and the peptide nucleic acid (PNA)-mediated polymerase chain reaction (PCR) clamping method in 134 NSCLCs and explored associations with clinicopathological factors. Next-generation sequencing (NGS) was used to validate the results of discordant cases. To increase the resolution of low-level somatic mutant molecules, PNA-mediated PCR clamping was used for mutant enrichment prior to NGS.ResultsTwenty-one (15.7%) cases were found to have the KRAS mutations using direct sequencing, with two additional cases by the PNA-mediated PCR clamping method. The frequencies of KRAS mutant alleles were 2% and 4%, respectively, using conventional NGS, increasing up to 90% and 89%, using mutant-enriched NGS. The KRAS mutation occurs more frequently in the tumors of smokers (p=.012) and in stage IV tumors (p=.032).ConclusionsDirect sequencing can accurately detect mutations, but, it is not always possible to obtain a tumor sample with sufficient volume. The PNA-mediated PCR clamping can rapidly provide results with sufficient sensitivity.

Highly Sensitive and Quantitative Detection of Mutations in v-Ki-ras2 Kirsten Rat Sarcoma Viral Oncogene by Quantitative Real-Time Polymerase Chain Reaction and Direct Sequencing With Peptide Nucleic Acid-Mediated Polymerase Chain Reaction Clamping

Highly Sensitive and Quantitative Detection of Mutations in v-Ki-ras2 Kirsten Rat Sarcoma Viral Oncogene by Quantitative Real-Time Polymerase Chain Reaction and Direct Sequencing With Peptide Nucleic Acid-Mediated Polymerase Chain Reaction Clamping

Follow-Up Study of K-ras Mutations in the Plasma of Patients With Pancreatic Cancer

We followed up the presence of Kirsten rat sarcoma (K-ras) mutations in plasma DNA and assessed its clinical value in patients with pancreatic cancer. Plasma samples (N = 430) of 56 patients with pancreatic cancer and 13 patients with pancreatitis were analyzed by real-time polymerase chain reaction using peptide nucleic acid-mediated polymerase chain reaction clamping. K-ras mutations could be detected in the plasma DNA of 20 patients with cancer (36%). No K-ras mutation was found in the plasma of patients with pancreatitis. In 7 (35%) of 20 patients with lowly or moderately elevated carbohydrate antigen 19.9 (CA 19-9) levels lower than 100 U/mL, the result of the assay was positive for K-ras mutation. The combination of K-ras and CA 19-9 level determination gave a sensitivity for the diagnosis of pancreatic cancer of 91% (40/44) of the patients. Thirteen of 35 patients with pancreatic cancer (102 plasma samples) with elevated CA 19-9 levels (>35 U/mL) and altered K-ras gene showed significant correlation with elevated CA 19-9 levels (P=0.048). The summary of our approach of noninvasive, convenient, extremely high-sensitive K-ras mutation analysis in plasma might provide diagnostic and prognostic information to clinicians but will not be sufficient in a standardized early diagnosis of pancreatic carcinoma. The combination with CA 19-9 assay is useful for detection and prognostic evaluation of pancreatic carcinoma.

One-Step Detection of c-kit Point Mutations Using Peptide Nucleic Acid-Mediated Polymerase Chain Reaction Clamping and Hybridization Probes

The prognostic significance of somatic activating codon 816 c-kit mutations in pediatric urticaria pigmentosa has not yet been established in detail. Detection of such mutations in archival paraffin-embedded biopsies is usually hampered by an abundance of surrounding normal cells. Here we describe a method for the selective amplification and specific detection of c-kit mutation Asp816-->Val in complete tissue sections cut from up to 24-year-old paraffin blocks. Peptide nucleic acid-mediated polymerase chain reaction clamping of the wild-type allele was combined with on-line mutation detection using oligonucleotide hybridization probes. In DNA extracted from HMC-1 cells heterozygously carrying the c-kit mutation Asp816-->Val, the one-tube assay allowed specific detection of this mutation in a more than 1000-fold excess of normal background DNA within 1 hour and without the need for additional analytical steps. In a series of 38 cases with pediatric urticaria pigmentosa we detected c-kit codons 815 and 816 mutations in 16 cases. Mutation detection did not correlate with clinical outcome after a mean follow-up of 11.2 years. In conclusion, the procedure described may represent an ideal screening tool for all kinds of clinical applications, using point mutations as markers of, for example, early events in carcinogenesis, circulating metastatic tumor cells, and minimal residual disease.

Detection of Genetic Point Mutations by Peptide Nucleic Acid-Mediated Polymerase Chain Reaction Clamping Using Paraffin-Embedded Specimens

Detection of Genetic Point Mutations by Peptide Nucleic Acid-Mediated Polymerase Chain Reaction Clamping Using Paraffin-Embedded Specimens