Activating STING1-dependent immune signaling in TP53 mutant and wild-type acute myeloid leukemia.

DNA methyltransferase inhibitors (DNMTis) reexpress hypermethylated genes in cancers and leukemias and also activate endogenous retroviruses (ERVs), leading to interferon (IFN) signaling, in a process known as viral mimicry. In the present study we show that in the subset of acute myeloid leukemias (AMLs) with mutations in TP53, associated with poor prognosis, DNMTis, important drugs for treatment of AML, enable expression of ERVs and IFN and inflammasome signaling in a STING-dependent manner. We previously reported that in solid tumors poly ADP ribose polymerase inhibitors (PARPis) combined with DNMTis to induce an IFN/inflammasome response that is dependent on STING1 and is mechanistically linked to generation of a homologous recombination defect (HRD). We now show that STING1 activity is actually increased in TP53 mutant compared with wild-type (WT) TP53 AML. Moreover, in TP53 mutant AML, STING1-dependent IFN/inflammatory signaling is increased by DNMTi treatment, whereas in AMLs with WT TP53, DNMTis alone have no effect. While combining DNMTis with PARPis increases IFN/inflammatory gene expression in WT TP53 AML cells, signaling induced in TP53 mutant AML is still several-fold higher. Notably, induction of HRD in both TP53 mutant and WT AMLs follows the pattern of STING1-dependent IFN and inflammatory signaling that we have observed with drug treatments. These findings increase our understanding of the mechanisms that underlie DNMTi + PARPi treatment, and also DNMTi combinations with immune therapies, suggesting a personalized approach that statifies by TP53 status, for use of such therapies, including potential immune activation of STING1 in AML and other cancers.

Epigenetic therapy induces transcription of inverted SINEs and ADAR1 dependency.

Cancer therapies that target epigenetic repressors can mediate their effects by activating retroelements within the human genome. Retroelement transcripts can form double-stranded RNA (dsRNA) that activates the MDA5 pattern recognition receptor1-6. This state of viral mimicry leads to loss of cancer cell fitness and stimulates innate and adaptive immune responses7,8. However, the clinical efficacy of epigenetic therapies has been limited. To find targets that would synergize with the viral mimicry response, we sought to identify the immunogenic retroelements that are activated by epigenetic therapies. Here we show that intronic and intergenic SINE elements, specifically inverted-repeat Alus, are the major source of drug-induced immunogenic dsRNA. These inverted-repeat Alus are frequently located downstream of 'orphan' CpG islands9. In mammals, the ADAR1 enzyme targets and destabilizes inverted-repeat Alu dsRNA10, which prevents activation of the MDA5 receptor11. We found that ADAR1 establishes a negative-feedback loop, restricting the viral mimicry response to epigenetic therapy. Depletion of ADAR1 in patient-derived cancer cells potentiates the efficacy of epigenetic therapy, restraining tumour growth and reducing cancer initiation. Therefore, epigenetic therapies trigger viral mimicry by inducing a subset of inverted-repeats Alus, leading to an ADAR1 dependency. Our findings suggest that combining epigenetic therapies with ADAR1 inhibitors represents a promising strategy for cancer treatment.

Oral cedazuridine/decitabine for MDS and CMML: a phase 2 pharmacokinetic/pharmacodynamic randomized crossover study.

This phase 2 study was designed to compare systemic decitabine exposure, demethylation activity, and safety in the first 2 cycles with cedazuridine 100 mg/decitabine 35 mg vs standard decitabine 20 mg/m2 IV. Adults with International Prognostic Scoring System intermediate-1/2- or high-risk myelodysplastic syndromes (MDS) or chronic myelomonocytic leukemia (CMML) were randomized 1:1 to receive oral cedazuridine/decitabine or IV decitabine in cycle 1, followed by crossover to the other treatment in cycle 2. All patients received oral cedazuridine/decitabine in subsequent cycles. Cedazuridine and decitabine were given initially as separate capsules in a dose-confirmation stage and then as a single fixed-dose combination (FDC) tablet. Primary end points: mean decitabine systemic exposure (geometric least-squares mean [LSM]) of oral/IV 5-day area under curve from time 0 to last measurable concentration (AUClast), percentage long interspersed nuclear element 1 (LINE-1) DNA demethylation for oral cedazuridine/decitabine vs IV decitabine, and clinical response. Eighty patients were randomized and treated. Oral/IV ratios of geometric LSM 5-day AUClast (80% confidence interval) were 93.5% (82.1-106.5) and 97.6% (80.5-118.3) for the dose-confirmation and FDC stages, respectively. Differences in mean %LINE-1 demethylation between oral and IV were ≤1%. Clinical responses were observed in 48 patients (60%), including 17 (21%) with complete response. The most common grade ≥3 adverse events regardless of causality were neutropenia (46%), thrombocytopenia (38%), and febrile neutropenia (29%). Oral cedazuridine/decitabine (100/35 mg) produced similar systemic decitabine exposure, DNA demethylation, and safety vs decitabine 20 mg/m2 IV in the first 2 cycles, with similar efficacy. This study is registered at www.clinicaltrials.gov as #NCT02103478.

Immuno-DNA binding directed template-free DNA extension and enzyme catalysis for sensitive electrochemical DNA methyltransferase activity assay and inhibitor screening.

Sensitive and accurate determination of DNA methyltransferase (DNA Mtase) activity is highly pursued for understanding fundamental biological processes related to DNA methylation, clinical disease diagnosis and drug discovery. Herein, we propose a new electrochemical immuno-DNA sensing platform for DNA Mtase activity assay and inhibitor screening. After homogeneous DNA methylation by CpG methyltransferase (M.SssI Mtase), the methylated DNA can be specifically recruited onto an electrode via its immunological binding with the immobilized anti-5-methylcytosine antibody. The recruited methylated DNA was simultaneously used as a substrate to facilitate successive template-free DNA extension and enzyme catalysis for the dual-step signal amplification of DNA Mtase activity. The developed immuno-DNA sensing strategy effectively integrates solution-phase DNA methylation, surface affinity binding recognition, and successive template-free DNA extension and enzyme catalysis-based signal amplification, rendering a highly specific, sensitive and accurate assay of DNA Mtase activity. A low detection limit of 0.039 U mL-1 could be achieved with a high selectivity. It was also applied for efficient evaluation of various inhibitors. Current affinity recognition of the immobilized antibody with methylated DNA switches the sensing platform into a DNA operation interface, facilitating the opportunity for combining various DNA-based signal amplification strategies to improve the detection performance. It would be used as a general strategy for the analysis of DNA Mtase activity, inhibitors and more analytes, and is anticipated to show potential for applications in disease diagnosis and drug discovery.

DNA methyltransferase inhibition reduces inflammation-induced colon tumorigenesis.

Chronic inflammation is strongly associated with an increased risk of developing colorectal cancer. DNA hypermethylation of CpG islands alters the expression of genes in cancer cells and plays an important role in carcinogenesis. Chronic inflammation is also associated with DNA methylation alterations and in a mouse model of inflammation-induced colon tumorigenesis, we previously demonstrated that inflammation-induced tumours have 203 unique regions with DNA hypermethylation compared to uninflamed epithelium. To determine if altering inflammation-induced DNA hypermethylation reduces tumorigenesis, we used the same mouse model and treated mice with the DNA methyltransferase (DNMT) inhibitor decitabine (DAC) throughout the tumorigenesis time frame. DAC treatment caused a significant reduction in colon tumorigenesis. The tumours that did form after DAC treatment had reduced inflammation-specific DNA hypermethylation and alteration of expression of associated candidate genes. When compared, inflammation-induced tumours from control (PBS-treated) mice were enriched for cell proliferation associated gene expression pathways whereas inflammation-induced tumours from DAC-treated mice were enriched for interferon gene signatures. To further understand the altered tumorigenesis, we derived tumoroids from the different tumour types. Interestingly, tumoroids derived from inflammation-induced tumours from control mice maintained many of the inflammation-induced DNA hypermethylation alterations and had higher levels of DNA hypermethylation at these regions than tumoroids from DAC-treated mice. Importantly, tumoroids derived from inflammation-induced tumours from the DAC-treated mice proliferated more slowly than those derived from the inflammation-induced tumours from control mice. These studies suggest that inhibition of inflammation-induced DNA hypermethylation may be an effective strategy to reduce inflammation-induced tumorigenesis.

Identification of a novel quinoline-based DNA demethylating compound highly potent in cancer cells.

BACKGROUND: DNA methyltransferases (DNMTs) are epigenetic enzymes involved in embryonic development, cell differentiation, epithelial to mesenchymal transition, and control of gene expression, whose overexpression or enhanced catalytic activity has been widely reported in cancer initiation and progression. To date, two DNMT inhibitors (DNMTi), 5-azacytidine (5-AZA) and 5-aza-2'-deoxycytidine (DAC), are approved for the treatment of myelodysplastic syndromes and acute myeloid leukemia. Nevertheless, they are chemically instable and quite toxic for healthy cells; thus, the discovery of novel DNMTi is urgent. RESULTS: Here, we report the identification of a new quinoline-based molecule, MC3353, as a non-nucleoside inhibitor and downregulator of DNMT. This compound was able, in promoter demethylating assays, to induce enhanced green fluorescence protein (EGFP) gene expression in HCT116 cells and transcription in a cytomegalovirus (CMV) promoter-driven luciferase reporter system in KG-1 cells. Moreover, MC3353 displayed a strong antiproliferative activity when tested on HCT116 colon cancer cells after 48 h of treatment at 0.5 µM. At higher doses, this compound provided a cytotoxic effect in double DNMT knockout HCT116 cells. MC3353 was also screened on a different panel of cancer cells (KG-1 and U-937 acute myeloid leukemia, RAJI Burkitt's lymphoma, PC-3 prostate cancer, and MDA-MB-231 breast cancer), where it arrested cell proliferation and reduced viability after 48 h of treatment with IC50 values ranging from 0.3 to 0.9 µM. Compared to healthy cell models, MC3353 induced apoptosis (e.g., U-937 and KG-1 cells) or necrosis (e.g., RAJI cells) at lower concentrations. Importantly, together with the main DNMT3A enzyme inhibition, MC3353 was also able to downregulate the DNMT3A protein level in selected HCT116 and PC-3 cell lines. Additionally, this compound provided impairment of the epithelial-to-mesenchymal transition (EMT) by inducing E-cadherin while reducing matrix metalloproteinase (MMP2) mRNA and protein levels in PC-3 and HCT116 cells. Last, tested on a panel of primary osteosarcoma cell lines, MC3353 markedly inhibited cell growth with low single-digit micromolar IC50 ranging from 1.1 to 2.4 µM. Interestingly, in Saos-2 osteosarcoma cells, MC3353 induced both expression of genes and mineralized the matrix as evidence of osteosarcoma to osteoblast differentiation. CONCLUSIONS: The present work describes MC3353 as a novel DNMTi displaying a stronger in cell demethylating ability than both 5-AZA and DAC, providing re-activation of the silenced ubiquitin C-terminal hydrolase L1 (UCHL1) gene. MC3353 displayed dose- and time-dependent antiproliferative activity in several cancer cell types, inducing cell death and affecting EMT through E-cadherin and MMP2 modulation. In addition, this compound proved efficacy even in primary osteosarcoma cell models, through the modulation of genes involved in osteoblast differentiation.

Photoelectrochemical determination of the activity of M.SssI methyltransferase, and a method for inhibitor screening.

A photoelectrochemical (PEC) method is described for the determination of the activity of M.SssI methyltransferase (MTase). The assay relies on enzyme-linkage reactions and a DNA intercalator Ru(bpy)2(dppz)2+ (where bpy is 2,2'-bipyridine, and dppz is dipyrido[3,2-a:2',3'-c]phenazine) which both serves as a PEC signal. The PEC electrode was obtained by immobilizing 5'-amino modified DNA strands (containing the methylation recognition site 5'-CCGG-3') on a polyethylenimine (PEI) coated ITO/SnO2 electrode with glutaraldehyde as crosslinking agent. In the presence of MTase and S-adenosyl-L-methionine, the 5'-CCGG-3' sequence in the DNA on the electrode is methylated. This protects the DNA strands from the shear of the methylation-sensitive restriction endonuclease HpaII. Consequently, more intact DNA strands remain on the surface of the electrode, providing more sites for Ru(bpy)2(dppz)2+ binding which in turn results in a high PEC response. The result demonstrates that the photocurrent increases linearly with the activity of MTase from 5 to 80 U·mL-1, and the limit of detection is 0.45 U·mL-1. The other MTases does not enhance the photocurrent, suggesting good selectivity of the assay. The method was also applied to rapid evaluate and screen the inhibitors of MTase. This strategy can be utilized to determinate the activity of other DNA MTases with specific DNA sequence. Graphical abstract Schematic presentation of a photoelectrochemical assay based on enzyme-linkage reactions and a photo electrochemical probe combined with the oxalic acid involved cyclic amplification system for the determination of methyltransferase activity.

Commercial glucometer as signal transducer for simple evaluation of DNA methyltransferase activity and inhibitors screening.

DNA methyltransferase (MTase) plays an important role in many biological processes and has been recognized as a predictive cancer biomarker far before other signs of malignancy and a therapeutic target in cancer treatment. Thus simple and sensitive determination of DNA MTase activity is urgently required. The commercially available glucometer is considered as the most successful point-of-care (POC) sensor up to date, and researchers extend its application in monitoring different types of targets rather than only glucose. Here, we developed a simple strategy for the sensitive detection of the DNA MTase (using M.SssI as an example) activity by using a glucometer as the signal transducer. A S1/S2 hybrid probe was designed including a specific recognition sequence for both DNA MTase and restriction endonuclease, and a complementary sequence for biotin-S3. Firstly, the S1/S2 hybrid probe was self-assembled on the gold electrode and methylated by M.SssI MTase to form the methylated dsDNA. Then, HpaII endonuclease specifically cleaved the residue of the unmethylated dsDNA. Subsequently, biotin-S3 hybridized with the overhang sequence of the methylated dsDNA. Finally, the biotin tag was successively combined with streptavidin (STV) and biotin-invertase. The invertase efficiently catalyzed the hydrolysis of sucrose to generate abundant glucose, which led to an amplified response of glucometer. This strategy could detect DNA MTase activity as low as 0.3 U mL-1 with good selectivity against other two cytosine MTases (HaeIII MTase and AluI MTase), and be successfully applied for screening the DNA MTase inhibitors (5-azacytidine and 5-aza-2'-deoxycytidine), implying our proposed method holds great promising application in early cancer diagnosis and therapeutics.

Aberrant epigenetic regulation of GABRP associates with aggressive phenotype of ovarian cancer.

Metastasis is a major cause of therapeutic failure in ovarian cancer. To elucidate molecular mechanisms of ovarian cancer metastasis, we previously established a metastatic xenograft mouse model using human ovarian carcinoma SK-OV-3 cells. Using gene expression profiling, we found that γ-aminobutyric acid (GABA)A receptor π subunit (GABRP) expression was upregulated (>4-fold) in metastatic tissues from our xenograft mice compared with SK-OV-3 cells. Importantly, GABRP knockdown diminished the migration and invasion of SK-OV-3 cells, and reduced extracellular signal-regulated kinase (ERK) activation while overexpression of GABRP exhibited significantly increased cell migration, invasion and ERK activation. Moreover, treatment with the mitogen-activated protein kinase (MAPK)/ERK kinase (MEK) inhibitor U0126 similarly suppressed the migration and invasion of SK-OV-3 cells, implying that GABRP promotes these cellular behaviors by activating the MAPK/ERK pathway. Using genome-wide DNA methylation profiling, we identified hypomethylated CpG sites in the GABRP promoter in metastatic tissues from the xenograft mice compared with SK-OV-3 cells. Treatment with a DNA methyltransferase inhibitor demonstrated that methylation at -963 bp from the GABRP transcription start site (-963 CpG site) was critical for the epigenetic regulation of GABRP. Finally, we analyzed human ovarian cancer patient samples and showed DNA hypomethylation at the GABRP -963 CpG site in advanced stage, but not early-stage, primary tumors compared with their paired normal tissues. These findings suggest that GABRP enhances the aggressive phenotype of ovarian cancer cells, and that the DNA methylation status of the GABRP -963 CpG site may be useful for predicting the metastatic potential in ovarian cancer patients.

RECQ1 helicase is involved in replication stress survival and drug resistance in multiple myeloma.

Multiple myeloma (MM) is a plasma cell cancer with poor survival, characterized by the expansion of multiple myeloma cells (MMCs) in the bone marrow. Using a microarray-based genome-wide screen for genes responding to DNA methyltransferases (DNMT) inhibition in MM cells, we identified RECQ1 among the most downregulated genes. RecQ helicases are DNA unwinding enzymes involved in the maintenance of chromosome stability. Here we show that RECQ1 is significantly overexpressed in MMCs compared to normal plasma cells and that increased RECQ1 expression is associated with poor prognosis in three independent cohorts of patients. Interestingly, RECQ1 knockdown inhibits cells growth and induces apoptosis in MMCs. Moreover, RECQ1 depletion promotes the development of DNA double-strand breaks, as evidenced by the formation of 53BP1 foci and the phosphorylation of ataxia-telangiectasia mutated (ATM) and histone variant H2A.X (H2AX). In contrast, RECQ1 overexpression protects MMCs from melphalan and bortezomib cytotoxicity. RECQ1 interacts with PARP1 in MMCs exposed to treatment and RECQ1 depletion sensitizes MMCs to poly(ADP-ribose) polymerase (PARP) inhibitor. DNMT inhibitor treatment results in RECQ1 downregulation through miR-203 deregulation in MMC. Altogether, these data suggest that association of DNA damaging agents and/or PARP inhibitors with DNMT inhibitors may represent a therapeutic approach in patients with high RECQ1 expression associated with a poor prognosis.

Quantitation of DNA methyltransferase activity via chronocoulometry in combination with rolling chain amplification.

In this paper, a rolling chain amplification (RCA) strategy was proposed for chronocoulometric detection of DNA methyltransferase (MTase) activity. Briefly, after the double DNA helix structure was assembled on the surface of gold electrode, it was first methylated by M. SssI MTase and then RCA was realized in the presence of E. coli and phi29 DNA polymerase. Successively, numerous hexaammineruthenium (III) chloride ([Ru(NH3)6)(3+), RuHex) were adsorbed on replicons by electrostatic interaction and generated a large electrochemical readout, the signal was "on". On the contrary, in the absence of M. SssI MTase, the methylated CpG site in the unmethylated double DNA helix structure could be specifically recognized and cleaved by HpaII, resulting in a disconnection of RCA from the electrode. This led seldom RuHex to be absorbed onto the surface of electrode, the signal was "off". Based on the proposed strategy, the activity of M. SssI MTase was assayed in the range of 0.5-60U/mL with a detection limit of 0.09U/mL (S/N=3). In addition, the inhibition of procaine and epicatechin on M. SssI MTase activity was evaluated. When the proposed method was applied in complex matrix such as human serum samples, acceptable accuracy, precision and high sensitivity were achieved. Therefore, the proposed method was a potential useful mean for clinical diagnosis and drug development.

Multicomponent Analysis of the Differential Induction of Secondary Metabolite Profiles in Fungal Endophytes.

Small molecule histone deacetylase (HDAC) and DNA methyltransferase (DNMT) inhibitors are commonly used to perturb the production of fungal metabolites leading to the induction of the expression of silent biosynthetic pathways. Several reports have described the variable effects observed in natural product profiles in fungi treated with HDAC and DNMT inhibitors, such as enhanced chemical diversity and/or the induction of new molecules previously unknown to be produced by the strain. Fungal endophytes are known to produce a wide variety of secondary metabolites (SMs) involved in their adaptation and survival within higher plants. The plant-microbe interaction may influence the expression of some biosynthetic pathways, otherwise cryptic in these fungi when grown in vitro. The aim of this study was to setup a systematic approach to evaluate and identify the possible effects of HDAC and DNMT inhibitors on the metabolic profiles of wild type fungal endophytes, including the chemical identification and characterization of the most significant SMs induced by these epigenetic modifiers.

Evaluation of DNA methyltransferase activity and inhibition via chiroplasmonic assemblies of gold nanoparticles.

Circular dichroism spectroscopy has been explored for detection of methyltransferase activity and inhibition based on DNA-induced chiroplasmonic assemblies of gold nanoparticles and endonuclease HpaII. Good accuracy, precision and sensitivity are obtained in complex matrices such as human serum samples, which is significant for clinical diagnosis and drug development.

Label-free electrochemical detection of methyltransferase activity and inhibitor screening based on endonuclease HpaII and the deposition of polyaniline.

Detection of DNA methylation and methyltransferase (MTase) activity are important in determining human cancer because aberrant methylation was linked to cancer initiation and progression. In this work, we proposed an electrochemical method for sensitive detection of DNA methylation and MTase activity based on methylation sensitive restriction endonuclease HpaII and the deposition of polyaniline (PANI) catalyzed by HRP-mimicking DNAzyme. In the presence of methylated DNA, HRP-mimicking DNAzyme catalyzed the polymerization of aniline on the dsDNA template, producing huge DPV current. In the presence of non-methylated DNA, dsDNA are cleaved and digested by HpaII and exonuclease III, as a result, no PANI are deposited. This method can be used to determine DNA methylation at the site of CpG. It exhibits a wide linear response toward M.SssI MTase activity in the range of 0.5-0.6 U mL(-1) with the detection limit of 0.12 U mL(-1). G-rich DNA forms HRP mimicking DNAzyme, which avoids complex labeling procedures and is robust. The method is simple, reliable, sensitive and specific, which has been successfully applied in human serum samples and been used to screen the inhibitors. Thus, the proposed method may be a potential and powerful tool for clinical diagnosis and drug development in the future.

DNA specific fluorescent symmetric dimeric bisbenzimidazoles DBP(n): the synthesis, spectral properties, and biological activity.

A series of new fluorescent symmetric dimeric bisbenzimidazoles DBP(n) bearing bisbenzimidazole fragments joined by oligomethylene linkers with a central 1,4-piperazine residue were synthesized. The complex formation of DBP(n) in the DNA minor groove was demonstrated. The DBP(n) at micromolar concentrations inhibit in vitro eukaryotic DNA topoisomerase I and prokaryotic DNA methyltransferase (MTase) M.SssI. The DBP(n) were soluble well in aqueous solutions and could penetrate cell and nuclear membranes and stain DNA in live cells. The DBP(n) displayed a moderate effect on the reactivation of gene expression.

G-quadruplex functionalized nano mesoporous silica for assay of the DNA methyltransferase activity.

The abnormal level of DNA methyltransferase (MTase) may cause the aberrant DNA methylation, which has been found being associated with a growing number of human diseases, so it is necessary to create a sensitive and selective method to detect DNA MTase activity. In this paper, a new type of DNA functionalized nano mesoporous silica (MSNs) was creatively introduced to the detection of DNA MTase activity with G-quadruplex as a lock for signal molecule to release. The method was carried out by designing a particular DNA which could fold into G-quadruplex and complement with probe DNA. Next, MSNs was prepared before blocking methylene blue (MB) by G-quadruplex. Probe DNA was then fixed on gold nanoparticles modified glass carbon electrode, and the material was able to be transferred to the surface of electrode by DNA hybridization. After methylation of DNA MTase and the cutting of restriction endonuclease, the electrode was transferred to phosphate buffer solution (pH 9.0) for the releasing of MB. The response of differential pulse voltammetry was obtained from the release of MB. Consequently, the difference of signals with or without methylation could prove the assay of M. SssI MTase activity. The results showed that the responses from MB increased linearly with the increasing of the M. SssI MTase concentrations from 0.28 to 50UmL(-1). The limit of detection was 0.28UmL(-1). In addition, Zebularine, a nucleoside analog of cytidine, was utilized for studying the inhibition activity of M. SssI MTase.

Distinct mechanisms underlie oral vs aboral regeneration in the cnidarian Hydractinia echinata.

Cnidarians possess remarkable powers of regeneration, but the cellular and molecular mechanisms underlying this capability are unclear. Studying the hydrozoan Hydractinia echinata we show that a burst of stem cell proliferation occurs following decapitation, forming a blastema at the oral pole within 24 hr. This process is necessary for head regeneration. Knocking down Piwi1, Vasa, Pl10 or Ncol1 expressed by blastema cells inhibited regeneration but not blastema formation. EdU pulse-chase experiments and in vivo tracking of individual transgenic Piwi1(+) stem cells showed that the cellular source for blastema formation is migration of stem cells from a remote area. Surprisingly, no blastema developed at the aboral pole after stolon removal. Instead, polyps transformed into stolons and then budded polyps. Hence, distinct mechanisms act to regenerate different body parts in Hydractinia. This model, where stem cell behavior can be monitored in vivo at single cell resolution, offers new insights for regenerative biology.

Single Amino Acid Mutation Controls Hole Transfer Dynamics in DNA-Methyltransferase HhaI Complexes.

Different mutagenic effects are generated by DNA oxidation that implies the formation of radical cation states (so-called holes) on purine nucleobases. The interaction of DNA with proteins may protect DNA from oxidative damage owing to hole transfer (HT) from the stack to aromatic amino acids. However, how protein binding affects HT dynamics in DNA is still poorly understood. Here, we report a computational study of HT in DNA complexes with methyltransferase HhaI with the aim of elucidating the molecular factors that explain why long-range DNA HT is inhibited when the glutamine residue inserted in the double helix is mutated into a tryptophan. We combine molecular dynamics, quantum chemistry, and kinetic Monte Carlo simulations and find that protein binding stabilizes the energies of the guanine radical cation states and significantly impacts the corresponding electronic couplings, thus determining the observed behavior, whereas the formation of a tryptophan radical leads to less efficient HT.

A novel signal-on strategy for M.SssI methyltransfease activity analysis and inhibitor screening based on photoelectrochemical immunosensor.

In this work, a novel signal-on photoelectrochemical (PEC) immunosensor was fabricated for M.SssI methyltransfease (MTase) activity analysis and inhibitor screening based on an in situ electron donor producing strategy, where the anti-5-methylcytosine antibody was selected as DNA CpG methylation recognition unit, gold nanoparticle labeled streptavidin (SA-AuNPs) as signal amplification unit and alkaline phosphatase conjugated biotin (ALP-Biotin) as enzymatic unit. In the presence of M.SssI MTase, hairpin DNA1 containing the palindromic sequences of 5'-CCGG-3' in its stem was methylated. After hybridization with biotin-conjugated DNA2, the stem-loop structure of the hairpin DNA1 was unfolded and the duplex strand DNA (dsDNA) was formed. Then, the dsDNA was captured on the surface of anti-5-methylcytosine antibody modified electrode through the specific immuno-reaction. Afterwards, SA-AuNPs and ALP-Biotin was further captured on the electrode surface through the specific reaction between biotin and streptavidin. Under the catalysis effect of ALP towards ascorbic acid 2-phosphate trisodium salt (AAP), ascorbic acid (AA) was in situ produced as electron donor and a strong PEC response was obtained. The fabricated biosensor showed high detection sensitivity with low detection limit of 0.33unit/mL for M.SssI MTase. Furthermore, the inhibition research suggested that RG108 could inhibit the M.SssI MTase activity with the IC50 value of 152.54nM.