The launch of the MinION Access Program has caused much activity within the scientific community. MinION represents a keenly anticipated, novel addition to the current melange of commercial sequencers. Driven by the nanopore sequencing mechanism that requires minimal sample manipulation, the device is capable of generating long sequence reads in sizes (up to or exceeding 50 kb) that surpass those of all other platforms. One notable advantage of this feature is that long-range haplotypes can be more accurately resolved; such advantage is particularly pertinent to the genotyping of complex loci such as genes encoding the human leukocyte antigens, which are pivotal determinants of drug hypersensitivity. With this timely, albeit brief, review, we set out to examine the applications on which MinION has been tested thus far, the bioinformatics workflow tailored to the unique characteristics of its extended sequence reads, the device's potential utility in the detection of genetic markers for drug hypersensitivity, and how it may eventually evolve to become fit for diagnostic purposes in the clinical setting.
Azathioprine and 6-mercaptopurine, often referred to as thiopurine compounds, are commonly used in the management of inflammatory bowel disease. However, patients receiving these drugs are prone to developing adverse drug reactions or therapeutic resistance. Achieving predefined levels of two major thiopurine metabolites, 6-thioguanine nucleotides and 6-methylmercaptopurine, is a long-standing clinical practice in ensuring therapeutic efficacy; however, their correlation with treatment response is sometimes unclear. Various genetic markers have also been used to aid the identification of patients who are thiopurine-sensitive or refractory. The recent discovery of novel Asian-specific DNA variants, namely those in the NUDT15 gene, and their link to thiopurine toxicity, have led clinicians and scientists to revisit the utility of Caucasian biomarkers for Asian individuals with inflammatory bowel disease. In this review, we explore the limitations associated with the current methods used for therapeutic monitoring of thiopurine metabolites and how the recent discovery of ethnicity-specific genetic markers can complement thiopurine metabolites measurement in formulating a strategy for more accurate prediction of thiopurine response. We also discuss the challenges in thiopurine therapy, alongside the current strategies used in patients with reduced thiopurine response. The review is concluded with suggestions for future work aiming at using a more comprehensive approach to optimize the efficacy of thiopurine compounds in inflammatory bowel disease.
We compared four brands of microtubes with respect to their suitability for long-range polymerase chain reactions (PCRs). One of the four brands was found to have an inhibitory effect, decreasing PCR yields. The effect was universal across different PCR or enzyme systems. Increased ultraviolet absorbance suggests leaching of unknown chemical species into PCR mixtures. However, this could not be confirmed by high-performance liquid chromatography-mass spectrometry analysis. Nevertheless, our article demonstrates a clear impact of the choice of microtubes on long-range PCR success. Due consideration should be given to the PCR microtubes when determining optimal reaction conditions for long-range PCR.
We report two cases of metoclopramide-induced acute dystonia in pregnant women and consider the role of genetic variation in the pathogenesis of the adverse effect. By whole-gene sequencing, we found that both women were CYP2D6 poor metabolizers. We theorize that CYP2D6 governs the risk of metoclopramide-related acute dystonia through its role in the synthesis of serotonin, which inhibits the dopamine tone. The effect of CYP2D6 poor metabolism is exaggerated by rises in the estrogen levels during pregnancy, as the hormone augments dopamine sensitivity. Together, the two factors may create a hyper-dopaminergic state that is easily upset by metoclopramide, resulting in acute dystonia.
Polymerase chain reaction (PCR) is an oft-used preparatory technique in amplifying specific DNA regions for downstream analysis. The size of an amplicon was initially limited by errors in nucleotide polymerization and template deterioration during thermal cycling. A variant of PCR, designated long-range PCR, was devised to counter these drawbacks and enable the amplification of large fragments exceeding a few kb. In this chapter we describe a protocol for long-range PCR, which we have adopted to obtain products of 6.6, 7.2, 13, and 20 kb from human genomic DNA samples.
Cisplatin is the first-line chemotherapeutic agent for the treatment of oral squamous cell carcinoma (OSCC). However, the intrinsic or acquired resistance against cisplatin remains a major obstacle to treatment efficacy in OSCC. Recently, mitochondrial DNA (mtDNA) alterations have been reported in a variety of cancers. However, the role of mtDNA alterations in OSCC has not been comprehensively studied. In this study, we evaluated the correlation between mtDNA alterations (mtDNA content, point mutations, large-scale deletions, and methylation status) and cisplatin sensitivity using two OSCC cell lines, namely SAS and H103, and stem cell-like tumour spheres derived from SAS. By microarray analysis, we found that the tumour spheres profited from aberrant lipid and glucose metabolism and became resistant to cisplatin. By qPCR analysis, we found that the cells with less mtDNA were less responsive to cisplatin (H103 and the tumour spheres). Based on the findings, we theorised that the metabolic changes in the tumour spheres probably resulted in mtDNA depletion, as the cells suppressed mitochondrial respiration and switched to an alternative mode of energy production, i.e. glycolysis. Then, to ascertain the origin of the variation in mtDNA content, we used MinION, a nanopore sequencer, to sequence the mitochondrial genomes of H103, SAS, and the tumour spheres. We found that the lower cisplatin sensitivity of H103 could have been caused by a constellation of genetic and epigenetic changes in its mitochondrial genome. Future work may look into how changes in mtDNA translate into an impact on cell function and therefore cisplatin response.
Preferential conversion of azathioprine or 6-mercaptopurine into methylated metabolites is a major cause of thiopurine resistance. To seek potentially Mendelian causes of thiopurine hypermethylation, we recruited 12 individuals who exhibited extreme therapeutic resistance while taking azathioprine or 6-mercaptopurine and performed whole-exome sequencing (WES) and copy-number variant analysis by array-based comparative genomic hybridisation (aCGH). Exome-wide variant filtering highlighted four genes potentially associated with thiopurine metabolism (ENOSF1 and NFS1), transport (SLC17A4) or therapeutic action (RCC2). However, variants of each gene were found only in two or three patients, and it is unclear whether these genes could influence thiopurine hypermethylation. Analysis by aCGH did not identify any unusual or pathogenic copy-number variants. This suggests that if causative mutations for the hypermethylation phenotype exist they may be heterogeneous, occurring in several different genes, or they may lie within regulatory regions not captured by WES. Alternatively, hypermethylation may arise from the involvement of multiple genes with small effects. To test this hypothesis would require recruitment of large patient samples and application of genome-wide association studies.
Whole-exome sequencing (WES) has been widely used for analysis of human genetic diseases, but its value for the pharmacogenomic profiling of individuals is not well studied. Initially, we performed an in-depth evaluation of the accuracy of WES variant calling in the pharmacogenes CYP2D6 and CYP2C19 by comparison with MiSeq(®) amplicon sequencing data (n = 36). This analysis revealed that the concordance rate between WES and MiSeq(®) was high, achieving 99.60% for variants that were called without exceeding the truth-sensitivity threshold (99%), defined during variant quality score recalibration (VQSR). Beyond this threshold, the proportion of discordant calls increased markedly. Subsequently, we expanded our findings beyond CYP2D6 and CYP2C19 to include more genes genotyped by the iPLEX(®) ADME PGx Panel in the subset of twelve samples. WES performed well, agreeing with the genotyping panel in approximately 99% of the selected pass-filter variant calls. Overall, our results have demonstrated WES to be a promising approach for pharmacogenomic profiling, with an estimated error rate of lower than 1%. Quality filters, particularly VQSR, are important for reducing the number of false variants. Future studies may benefit from examining the role of WES in the clinical setting for guiding drug therapy.
Hereditary or developmental neurological disorders (HNDs or DNDs) affect the quality of life and contribute to the high mortality rates among neonates. Most HNDs are incurable, and the search for new and effective treatments is hampered by challenges peculiar to the human brain, which is guarded by the near-impervious blood-brain barrier. Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR), a gene-editing tool repurposed from bacterial defense systems against viruses, has been touted by some as a panacea for genetic diseases. CRISPR has expedited the research into HNDs, enabling the generation of in vitro and in vivo models to simulate the changes in human physiology caused by genetic variation. In this review, we describe the basic principles and workings of CRISPR and the modifications that have been made to broaden its applications. Then, we review important CRISPR-based studies that have opened new doors to the treatment of HNDs such as fragile X syndrome and Down syndrome. We also discuss how CRISPR can be used to generate research models to examine the effects of genetic variation and caffeine therapy on the developing brain. Several drawbacks of CRISPR may preclude its use at the clinics, particularly the vulnerability of neuronal cells to the adverse effect of gene editing, and the inefficiency of CRISPR delivery into the brain. In concluding the review, we offer some suggestions for enhancing the gene-editing efficacy of CRISPR and how it may be morphed into safe and effective therapy for HNDs and other brain disorders.
Tissues become more rigid during tumorigenesis and have been identified as a driving factor for tumor growth. Here, we highlight the concept of tissue rigidity, contributing factors that increase tissue rigidity, and mechanisms that promote tumor growth initiated by increased tissue rigidity. Various factors lead to increased tissue rigidity, promoting tumor growth by activating focal adhesion kinase (FAK) and Rho-associated kinase (ROCK). Consequently, result in recruitment of cancer-associated fibroblasts (CAFs), epithelial-mesenchymal transition (EMT) and tumor protection from immunosurveillance. We also discussed the rationale for targeting tumor tissue rigidity and its potential for cancer treatment.
Next generation DNA sequencing and analysis of amplicons spanning the pharmacogene CYP2D6 suggested that the Nextera transposase used for fragmenting and providing sequencing priming sites displayed a targeting bias. This manifested as dramatically lower sequencing coverage at sites in the amplicon that appeared likely to form G-quadruplex structures. Since secondary DNA structures such as G-quadruplexes are abundant in the human genome, and are known to interact with many other proteins, we further investigated these sites of low coverage. Our investigation revealed that G-quadruplex structures are formed in vitro within the CYP2D6 pharmacogene at these sites, and G-quadruplexes can interact with the hyperactive Tn5 transposase (EZ-Tn5) with high affinity. These findings indicate that secondary DNA structures such as G-quadruplexes may represent preferential transposon integration sites and provide additional evidence for the role of G-quadruplex structures in transposition or viral integration processes.
Lung cancer is one of the most lethal forms of cancer known to man, affecting millions of individuals worldwide. Despite advancements being made in lung cancer treatments, the prognosis of patients with the disease remains poor, particularly among patients with late‑stage lung cancer. The elucidation of the signaling pathways involved in lung cancer is a critical approach for the treatment of the disease. Over the past decades, accumulating evidence has revealed that Rho‑associated kinase (ROCK) is overexpressed in lung cancer and is associated with tumor growth. The present review discusses recent findings of ROCK signaling in the pathogenesis of lung cancer that were conducted in pre‑clinical studies. The significant role of ROCK in cancer cell apoptosis, proliferation, migration, invasion and angiogenesis is discussed. The present review also suggests the use of ROCK as a potential target for the development of lung cancer therapies, as ROCK inhibition can reduce multiple hallmarks of cancer, particularly by decreasing cancer cell migration, which is an initial step of metastasis.
Increased tissue rigidity is able to activate the Hippo signaling pathway, leading to YAP inactivation by phosphorylation and translocation into the cytoplasm. Accumulating evidence suggests that cytoplasmic pYAP serves as a tumor suppressor and could be a prognostic biomarker for several solid cancers. However, the relationship between tissue rigidity and cytoplasmic pYAP expression in the early stage of lung squamous cell carcinoma (SCC) remains elusive; this was determined in this study by using a mouse model. Female BALB/c mice were assigned into two groups (n = 6; the vehicle (VC) and the pre-malignant (PM) group, which received 70% acetone and 0.04 M N-nitroso-tris-chloroethylurea (NTCU) for 15 weeks, respectively. In this study, the formation of hyperplasia and metaplasia lesions was found in the PM group, indicating the pre-malignant stage of lung SCC. The pre-malignant tissue appeared to be more rigid as characterized by significantly higher (p < 0.05) epithelium thickness, proliferative activity, and collagen content than the VC group. The PM group also had a significantly higher (p < 0.05) cytoplasmic pYAP protein expression than the VC group. In conclusion, increased tissue rigidity may contribute to the upregulation of cytoplasmic pYAP expression, which may act as a tumor suppressor in the early stage of lung SCC.
Increased tissue rigidity is an emerging hallmark of cancer as it plays a critical role in promoting cancer growth. However, the field lacks a defined characterization of tissue rigidity in dual-stage carcinogenesis of lung squamous cell carcinoma (SCC) in vivo. Pre-malignant and malignant lung SCC was developed in BALB/c mice using N-nitroso-tris-chloroethylurea (NTCU). Picro sirius red staining and atomic force microscopy were performed to measure collagen content and collagen (diameter and rigidity), respectively. Then, the expression of tenascin C (TNC) protein was determined using immunohistochemistry staining. Briefly, all tissue rigidity parameters were found to be increased in the Cancer group as compared with the Vehicle group. Importantly, collagen content (33.63 ± 2.39%) and TNC expression (7.97 ± 2.04%) were found to be significantly higher (p < 0.05) in the Malignant Cancer group, as compared with the collagen content (18.08 ± 1.75%) and TNC expression (0.45 ± 0.53%) in the Pre-malignant Cancer group, indicating increased tissue rigidity during carcinogenesis of lung SCC. Overall, tissue rigidity of lung SCC was suggested to be increased during carcinogenesis as indicated by the overexpression of collagen and TNC protein, which may warrant further research as novel therapeutic targets to treat lung SCC effectively.
Stem cells such as induced pluripotent stem cells, embryonic stem cells, and hematopoietic stem and progenitor cells are growing in importance in disease modeling and regenerative medicine. The applications of CRISPR-based gene editing to create a mélange of disease and nondisease stem cell lines have further enhanced the utility of this innately versatile group of cells in the studies of human genetic disorders. Precise base edits can be achieved using a variety of CRISPR-centric approaches, particularly homology-directed repair and the recently developed base editors and prime editors. Despite its much-touted potential, editing single DNA bases is technically challenging. In this review, we discuss the strategies for achieving exact base edits in the creation of various stem cell-based models for use in elucidating disease mechanisms and assessing drug efficacy, and the unique characteristics of stem cells that warrant special considerations.
A multitude of factors can affect drug response in individuals. It is now well established that variations in genes, especially those coding for drug metabolising enzymes, can alter the pharmacokinetic and/or pharmacodynamic profile of a drug, impacting on efficacy and often resulting in drug-induced toxicity. The UDRUGS study is an initiative from the Carney Centre for Pharmacogenomics to biobank DNA and store associated clinical data from patients who have suffered rare and/or serious adverse drug reactions (ADRs). The aim is to provide a genetic explanation of drug-induced ADRs using methods ranging from Sanger sequencing to whole exome and whole genome sequencing. Participants for the UDRUGS study are recruited from various sources, mainly via referral through clinicians working in Canterbury District Health Board, but also from district health boards across New Zealand. Participants have also self-referred to us from word-of-mouth communication between participants. We have recruited various ADRs across most drug classes. Where possible, we have conducted genetic analyses in single or a cohort of cases to identify known and novel genetic association(s) to offer an explanation to why the ADR occurred. Any genetic results relevant to the ADR are communicated back to the referring clinician and/or participant. In conclusion, we have developed a programme for studying the genetic basis of severe, rare or unusual ADR cases resulting from pharmacological treatment. Genomic analyses could eventually identify most genetic variants that predispose to ADRs, enabling a priori detection of such variants with high throughput DNA tests.
Polymerase chain reaction (PCR) is a laboratory technique used to amplify a targeted region of DNA, demarcated by a set of oligonucleotide primers. Long-range PCR is a form of PCR optimized to facilitate the amplification of large fragments. Using the adapted long-range PCR protocol described in this chapter, we were able to generate PCR products of 6.6, 7.2, 13, and 20 kb from human genomic DNA samples. For some of the long PCRs, successful amplification was not possible without the use of PCR enhancers. Thus, we also evaluated the impact of some enhancers on long-range PCR and included the findings as part of this updated chapter.
Mice have served as an excellent model to understand the etiology of lung cancer for years. However, data regarding dual-stage carcinogenesis of lung squamous cell carcinoma (SCC) remain elusive. Therefore, we aim to develop pre-malignant (PM) and malignant (M) lung SCC in vivo using N-nitroso-tris-chloroethylurea (NTCU). BALB/C mice were allotted into two main groups; PM and M groups which received treatment for 15 and 30 weeks, respectively. Then, the mice in each main group were allotted into three groups; control, vehicle, and cancer (n = 6), which received normal saline, 70% acetone, and 0.04 M NTCU by skin painting, respectively. Histopathologically, we discovered a mix of hyperplasia, metaplasia, and dysplasia lesions in the PM group and intracellular bridge; an SCC feature in the M group. The M group was positive for cytokeratin 5/6 protein which confirmed the lung SCC subtype. We also found significantly higher (P
Single nucleotide polymorphisms (SNPs) could increase the susceptibility of individuals to develop obesity and type 2 diabetes (T2DM). Obesity and T2DM are closely related pathophysiologically, thus similar SNPs could mediate both these diseases, but this is rarely reported. Furthermore, limited studies have been performed to summarize SNP data in the Asian population compared to the Western population. In this study, we aimed to summarize SNPs that are associated with the development of obesity and T2DM among Asian populations. We searched six literature databases and Review Manager (RevMan) was used for meta-analysis. The pooled odds ratios (ORs) and 95% CIs were calculated with a random effects model for the heterogeneity among studies. The pooled analysis showed that rs9939609 (FTO gene) and rs17782313 and rs571312 (MC4R gene) are associated with obesity with an odd ratio (OR) of 1.37, 1.36 and 1.29 respectively. For T2DM, five SNPs, rs7903146 and rs12255372 (TCF7L2 gene), rs13266634 and rs11558471 (SLC30A8 gene) and rs2283228 (KCNQ1 gene) have also shown strong associations with T2DM at OR of 1.64, 1.61, 1.22, 1.29 and 1.60 respectively. This data could be used to develop a gene screening panel for assessing obesity and T2DM susceptibility.