Structure-activity features of purines and their receptors: implications in cell physiopathology

The purine molecular structure consists of fused pyrimidine and imidazole rings. Purines are main pieces that conform the structure of nucleic acids which rule the inheritance processes. Purines also work as metabolic intermediates in different cell functions and as messengers in the signaling pathways throughout cellular communication. Purines, mainly ATP and adenosine (ADO), perform their functional and pharmacological properties because of their structural/chemical characteristics that make them either targets of mutagenesis, mother frameworks for designing molecules with controlled effects (e.g. anti-cancer), or chemical donors (e.g., of methyl groups, which represent a potential chemoprotective action against cancer). Purines functions also come from their effect on specific receptors, channel-linked and G-protein coupled for ATP, and exclusively G-coupled receptors for ADO (also known as ADORAs), which are involved in cell signaling pathways, there, purines work as chemical messengers with autocrine, paracrine, and endocrine actions that regulate cell metabolism and immune response in tumor progression which depends on the receptor types involved in these signals. Purines also have antioxidant and anti-inflammatory properties and participate in the cell energy homeostasis. Therefore, purine physiology is important for a variety of functions relevant to cellular health; thus, when these molecules present a homeostatic imbalance, the stability and survival of the cellular systems become compromised.

Combined lead and zinc oxide-nanoparticles induced thyroid toxicity through 8-OHdG oxidative stress-mediated inflammation, apoptosis, and Nrf2 activation in rats

A human is exposed to a chemical mixture rather than a single chemical, particularly with the wide spread of nanomaterials. Therefore, the present study evaluated the combined exposure of lead acetate (Pb) and zinc oxide-nanoparticles (ZnO-NPs) compared to each metal alone on the thyroid gland of adult rats. A total of 30 adult male albino rats were divided into four groups, group I (control), group II received Pb (10 mg/kg), group III received ZnO-NPs (85 mg/kg) and group IV co-administrated the two metals in the same previous doses. The materials were gavaged for 8 weeks. The toxicity was assessed through several biochemical parameters. Our results revealed significant body weight reduction relative to increased thyroid weights, decreased both of serum-free triiodothyronine (FT3), tetra-iodothyronine (FT4), increased thyroid-stimulating hormone (TSH), increased serum and thyroid levels of Pb and zinc, significant elevation in tumor necrosis factor-α (TNF-α), reduction in interleukin 4 (IL4), upregulation of Bax, and downregulation of Bcl-2 genes. Additionally, there was significant overexpression of nuclear factor erythroid 2-related factor 2(Nrf2), 8-Hydroxydeoxyguanosine(8-OHdG), the elevation of tissues malondialdehyde (MDA), reduction of tissues total antioxidant capacity (TAC), and disruptive thyroid structural alterations in all metals groups with marked changes in the combined metals group. In conclusion, the combined exposure of Pb and ZnO-NPs induced pronounced toxic thyroid injury, pointing to additive effects in rats than the individual metal effects through different significant changes of disruptive thyroid structural alterations related to the loading of thyroid tissues with Pb and zinc metals producing oxidative stress that mediated inflammation and apoptosis.

Inhibitor development of MTH1 via high-throughput screening with fragment based library and MTH1 substrate binding cavity

MutT Homolog 1 (MTH1) has been proven to hydrolyze oxidized nucleotide triphosphates during DNA repair. It can prevent the incorporation of wrong nucleotides during DNA replication and mitigate cell apoptosis. In a cancer cell, abundant reactive oxygen species can lead to substantial DNA damage and DNA mutations by base-pairing mismatch. MTH1 could eliminate oxidized dNTP and prevent cancer cells from entering cell death. Therefore, inhibition of MTH1 activity is considered to be an anti-cancer therapeutic target. In this study, high-throughput screening techniques were combined with a fragment-based library containing 2,313 compounds, which were used to screen for lead compounds with MTH1 inhibitor activity. Four compounds with MTH1 inhibitor ability were selected, and compound MI0639 was found to have the highest effective inhibition. To discover the selectivity and specificity of this action, several derivatives based on the MTH1 and MI0639 complex structure were synthesized. We compared 14 complex structures of MTH1 and the various compounds in combination with enzymatic inhibition and thermodynamic analysis. Nanomolar-range IC₅₀ inhibition abilities by enzyme kinetics and K_d values by thermodynamic analysis were obtained for two compounds, named MI1020 and MI1024. Based on structural information and compound optimization, we aim to provide a strategy for the development of MTH1 inhibitors with high selectivity and specificity.

A Double-Edged Sword: The Anti-Cancer Effects of Emodin by Inhibiting the Redox-Protective Protein MTH1 and Augmenting ROS in NSCLC

Background: Reactive oxygen species (ROS), playing a two-fold role in tumorigenesis, are responsible for tumor formation and progression through the induction of genome instability and pro-oncogenic signaling. The same ROS is toxic to cancer cells at higher levels, oxidizing free nucleotide precursors (dNTPs) as well as damaging DNA leading to cell senescence. Research has highlighted the tumor cell-specific expression of a redox-protective phosphatase, MutT homolog 1 (MTH1), that performs the enzymatic conversion of oxidized nucleotides (like 8-oxo-dGTP) to their corresponding monophosphates, up-regulated in numerous cancers, circumventing their misincorporation into the genomic DNA and preventing damage and cell death. Methods: To identify novel natural small molecular inhibitors of MTH1 to be used as cancer therapeutic agents, molecular screening for MTH1 active site binders was performed from natural small molecular libraries. Emodin was identified as a lead compound for MTH1 active site functional inhibition and its action on MTH1 inhibition was validated on non-small cell lung cancer cellular models (NSCLC). Results: Our study provides strong evidence that emodin mediated MTH1 inhibition impaired NSCLC cell growth, inducing senescence. Emodin treatment enhanced the cellular ROS burdens, on one hand, damaged dNTP pools and inhibited MTH1 function on the other. Our work on emodin indicates that ROS is the key driver of cancer cell-specific increased DNA damage and apoptosis upon MTH1 inhibition. Consequently, we observed a time-dependent increase in NSCL cancer cell susceptibility to oxidative stress with emodin treatment. Conclusions: Based on our data, the anti-cancer effects of emodin as an MTH1 inhibitor have clinical potential as a single agent capable of functioning as a ROS inducer and simultaneous blocker of dNTP pool sanitation in the treatment of NSCL cancers. Collectively, our results have identified for the first time that the potential molecular mechanism of emodin function, increasing DNA damage and apoptosis in cancer cells, is via MTH1 inhibition.

The Significance of 8-oxoGsn in Aging-Related Diseases

Aging is a common risk factor for the occurrence and development of many diseases, such as Parkinson’s disease, Alzheimer’s disease, diabetes, hypertension, atherosclerosis and coronary heart disease, and cancer, among others, and is a key problem threatening the health and life expectancy of the elderly. Oxidative damage is an important mechanism involved in aging. The latest discovery pertaining to oxidative damage is that 8-oxoGsn (8-oxo-7,8-dihydroguanosine), an oxidative damage product of RNA, can represent the level of oxidative stress. The significance of RNA oxidative damage to aging has not been fully explained, but the relationship between the accumulation of 8-oxoGsn, a marker of RNA oxidative damage, and the occurrence of diseases has been confirmed in many aging-related diseases. Studying the aging mechanism, monitoring the aging level of the body and exploring the corresponding countermeasures are of great significance for achieving healthy aging and promoting public health and social development. This article reviews the progress of research on 8-oxoGsn in aging-related diseases.

The high expression of MTH1 and NUDT5 predict a poor survival and are associated with malignancy of esophageal squamous cell carcinoma

Background

MTH1 and NUDT5 effectively degrade nucleotides containing 8-oxoguanine. MTH1 and NUDT5 have been linked to the malignancy of multiple cancers. However, their functions in tumor growth and metastasis in esophageal squamous carcinoma (ESCC) remain obscure. Our present study aims to explore their prognostic value in ESCC and investigate their function in MTH1 or NUDT5-knockout tumor cells.

Methods

MTH1 and NUDT5 protein expression in ESCC adjacent normal tissues and tumor tissues was examined by immunohistochemistry staining. Kaplan–Meier curves were used to assess the association between their expression and overall survival (OS) in ESCC patients. Univariate and Multivariate Cox regression analyses were generated to determine the correlation between these protein expression and OS of ESCC patients. Protein expression in ESCC cell lines were measured by Western blotting. To explore the potential effects of the MTH1 and NUDT5 protein in ESCC, cell models with MTH1 or NUDT5 depletion were established. CCK-8, cell cycle, Western blotting, migration and invasion assays were performed.

Results

Our present study demonstrated that the levels of MTH1 and NUDT5 were upregulated in ESCC cell lines and ESCC tissues, the expression of MTH1 and NUDT5 in ESCC tissues was significantly higher than in adjacent non-tumorous, and higher levels of MTH1 and NUDT5 predicted a worse prognosis in patients with ESCC. MTH1 and NUDT5 are novel biomarkers of the progression of ESCC and a poor prognosis. We also found for the first time that the high expression of NUDT5 independently predicted lower OS in patients with ESCC (hazard ratio (HR) 1.751; 95% confidence interval (CI) [1.056–2.903]; p = 0.030). In addition, the depletion of MTH1 and NUDT5 strongly suppressed the proliferation of ESCC cells and significantly delayed the G1 phase of the cell cycle. Furthermore, we found that MTH1 and NUDT5 silencing inhibited epithelial–mesenchymal transition mainly by the MAPK/MEK/ERK dependent pathway, which in turn significantly decreased the cell migration and invasion of ESCC cells. Our results suggested that the overexpression of MTH1 and NUDT5 is probably involved in the tumor development and poor prognosis of ESCC.

Effects of Tomato Juice Intake on Salivary 8-Oxo-dG Levels as Oxidative Stress Biomarker after Extensive Physical Exercise

Reactive oxygen species (ROS) at a normal level are important molecules involved in several cellular processes including immune response and cell signalling. Overproduction of ROS may lead to elevated oxidative stress and consequently to age-related diseases. Most of the studies related to oxidative stress in humans have been done on blood samples. However, blood sampling might be painful, requires special qualified personnel, and has to be performed at medical centers. An alternative to blood is saliva. Saliva sampling is noninvasive and can be performed by the donor. Biomarker determination in saliva is becoming an important part of laboratory diagnosis, but method development is needed before it can be used in the clinics. In the present investigation, 16 donors performed extensive physical exercise by cycling and keeping their heart rate at 80% of maximum for 20 minutes. The physical activity was repeated 3 times: before tomato juice intake, after daily intake of 100 ml tomato juice during 3 weeks, and finally 3 weeks after finishing tomato juice intake (washout period). The level of the stress biomarker, salivary 8-oxo-dG, was determined before and after the physical activity. The results indicate that (a) 20 min extensive physical activity increases the level of 8-oxo-dG in saliva significantly (p = 0.0078) and (b) daily intake of 100 ml tomato juice may inhibit (p = 0.052) overproduction of salivary 8-oxo-dG by 20 min physical activity. We conclude that the 20 min extensive physical activity increases the level of salivary 8-oxo-dG in healthy donors and 100 ml daily intake of tomato juice may inhibit the increase of 8-oxo-dG in saliva.

Increased MTH1-specific 8-oxodGTPase activity is a hallmark of cancer in colon, lung and pancreatic tissue

Cellular homeostasis is dependent on a balance between DNA damage and DNA repair mechanisms. Cells are constantly assaulted by both exogenous and endogenous stimuli leading to high levels of reactive oxygen species (ROS) that cause oxidation of the nucleotide dGTP to 8-oxodGTP. If this base is incorporated into DNA and goes unrepaired, it can result in G > T transversions, leading to genomic DNA damage. MutT Homolog 1 (MTH1) is a nucleoside diphosphate X (Nudix) pyrophosphatase that can remove 8-oxodGTP from the nucleotide pool before it is incorporated into DNA by hydrolyzing it into 8-oxodGMP. MTH1 expression has been shown to be elevated in many cancer cells and is thought to be a survival mechanism by which a cancer cell can stave off the effects of high ROS that can result in cell senescence or death. It has recently become a target of interest in cancer because it is thought that inhibiting MTH1 can increase genotoxic damage and cytotoxicity. Determining the role of MTH1 in normal and cancer cells is confounded by an inability to reliably and directly measure its native enzymatic activity. We have used the chimeric ATP-releasing guanine-oxidized (ARGO) probe that combines 8-oxodGTP and ATP to measure MTH1 enzymatic activity in colorectal cancer (CRC), non-small cell lung cancer (NSCLC) and pancreatic ductal adenocarcinoma (PDAC) along with patient-matched normal tissue. MTH1 8-oxodGTPase activity is significantly increased in tumors across all three tissue types, indicating that MTH1 is a marker of cancer. MTH1 activity measured by ARGO assay was compared to mRNA and protein expression measured by RT-qPCR and Western blot in the CRC tissue pairs, revealing a positive correlation between ARGO assay and Western blot, but little correlation with RT-qPCR in these samples. The adoption of the ARGO assay will help in establishing the level of MTH1 activity in model systems and in assessing the effects of MTH1 modulation in the treatment of cancer.

Anticancer effect of (S)-crizotinib on osteosarcoma cells by targeting MTH1 and activating reactive oxygen species

MTH1 has become a new rising star in the field of ‘cancer phenotypic lethality’ and can be targeted in many kinds of tumors. This study aimed to explore the anticancer effect of MTH1-targeted drug (S)-crizotinib on osteosarcoma (OS) cells. We detected MTH1 expression in OS tissues and cells using immunohistochemistry and western blot. The effects of MTH1 on OS cell viability were explored using the siRNA technique and CCK8. The anticancer effects of the MTH1-targeted drug (S)-crizotinib on OS cells were explored by in-vitro assays. The intracellular 8-oxo-dGTP level and oxygen reactive species (ROS) of OS cells were detected by Cy3-conjugated avidin staining and dichlorofluorescein diacetate staining, respectively. The expression of MTH1 was significantly higher in OS tissues and cell lines than that in the corresponding adjacent tissues and osteoblastic cell line. The proliferation of OS cells was significantly inhibited through knockdown of MTH1 by siRNA technology. (S)-Crizotinib could inhibit the proliferation of OS cells with an increase in the apoptosis levels and causing G0/G1 arrest by targeting MTH1 and activating ROS. In addition, (S)-crizotinib could inhibit the migration of OS cells. (S)-Crizotinib could suppress the proliferation and migration, cause G0/G1 arrest, and increase the apoptosis level of OS cells by targeting MTH1 and activating ROS. This study will provide a promising therapeutic target and the theoretical basis for the clinical application of (S)-crizotinib in OS.

Overexpression of MTH1 and OGG1 proteins in ulcerative colitis-associated carcinogenesis

Oxidative stress, demonstrated by an accumulation of 8-hydroxy-2'-deoxyguanosine (8-OHdG), results in DNA damage, which is normally repaired by base excision repair enzymes including 8-OHdG DNA glycosylase (OGG1) and human MutY homolog (MUTYH), in addition to nucleotide pool sanitizing enzymes including MutT Homolog 1 (MTH1). Abnormalities of this repair system are present in various cancer types. The present study aimed to elucidate the clinicopathological significance of altered expression levels of inducible nitric oxide synthase (iNOS), 8-OHdG, OGG1, MTH1 and MUTYH in ulcerative colitis (UC) and UC-associated neoplasms. Immunohistochemical staining for these markers and p53 in 23 cases of UC-associated neoplasm (Group A, 14 carcinomas and nine dysplasias), 16 cases of UC without neoplasm (Group B) and 17 cases of normal colon specimens (Group C) was performed. Mutation analyses was conducted for KRAS proto-oncogene, GTPase (K-ras), tumor protein P53 (TP53) and isocitrate dehydrogenase (NADP (+)) 1, cytosolic (IDH1) genes. Immunohistochemically, the iNOS, 8-OHdG, OGG1 and MTH1 expression levels were increased in Groups A and B compared with Group C. The OGG1 and MTH1 expression levels in Group A were also increased compared with Group B. Group A and Group B exhibited increased cytoplasmic expression and decreased nuclear expression of MUTYH compared with Group C. Mutations of K-ras and TP53 were detected in 2/21 (9.5%) and 10/22 (45.5%) cases of Group A, respectively. IDH1 mutation was not detected in any cases. These findings suggest that, as a response to oxidative damage, OGG1 and MTH1 may be upregulated in UC through an inflammatory condition that progresses to cancer formation. Persisting oxidative damage stress may play a role in the pathogenesis of UC-associated tumors.

Serum 8-Oxo-dG as a Predictor of Sensitivity and Outcome of Radiotherapy and Chemotherapy of Upper Gastrointestinal Tumours

The level of oxidative stress is important in the initiation and progression of various age-related diseases, such as cancer. The level of oxidative stress may also play a significant role in cancer patients' response to treatment. We aimed to investigate whether serum 8-oxo-dG as a marker of oxidative stress is a predictor of tumour response. We used modified ELISA with a two-step filtration to analyse 8-oxo-dG in serum. The relationship between 8-oxo-dG levels, tumour response, and toxicity was studied in 19 oesophageal cancer patients who received radiotherapy and 16 gastric cancer patients who received chemotherapy. In the radiotherapy and the merged radio- and chemotherapy groups, the baseline levels of 8-oxo-dG were significantly lower in responder patients than in nonresponder patients and the increments after treatment were greater. In comparison with patients whose serum 8-oxo-dG levels decrease after treatment, patients with increasing levels had a longer median “progression-free survival.” Our results, although preliminary, suggest that serum levels of 8-oxo-dG may potentially be used to predict the sensitivity and outcome of radiotherapy and chemotherapy of upper gastrointestinal tumours. Patients with 8-oxo-dG levels that are low prior to treatment and subsequently increase after treatment may be more likely to benefit from the therapy.

The Ratio of Plasma and Urinary 8-oxo-Gsn Could Be a Novel Evaluation Index for Patients with Chronic Kidney Disease

Nucleic acid oxidation plays an important role in the pathophysiology progress of a variety of diseases. 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxo-dGsn) and 8-oxo-7,8-dihydroguanosine (8-oxo-Gsn), which originate from DNA and RNA oxidation, were the most widely used indicators for oxidative stress. The study investigated the relation between 8-oxo-dGsn, 8-oxo-Gsn, and CKD. 146 patients with CKD were divided into five disease stages, and their fasting blood and morning urine were collected. The levels of 8-oxo-dGsn and 8-oxo-Gsn in plasma and urine were quantified by LC-MS/MS. The ratio of urinary 8-oxo-Gsn to creatinine increased from stages 1 to 4 corresponding to the increased severity of CKD, but it decreased in stage 5. And plasma 8-oxo-Gsn gradually increased with the decline of renal function. In particular, the increased ratio of plasma and urine 8-oxo-Gsn in stage 5 exceeded the concentration of creatinine. This trend was similar to the estimated glomerular filtration rate (eGFR), which indicates that 8-oxo-Gsn could be an appropriate indicator for renal function. Our finding indicates that as the disease progresses, RNA oxidation is increased. The significant increase in the ratio of plasma and urinary 8-oxo-Gsn is a novel evaluation index of end-stage renal disease.

MutT-related proteins are novel progression and prognostic markers for colorectal cancer

Background

MutT-related proteins, including MTH1, MTH2, MTH3 and NUDT5, can effectively degrade 8-oxoGua-containing nucleotides. The MTH1 expression is elevated in many types of human tumors and MTH1 overexpression correlates with the tumor pathological stage and poor prognosis. However, the expression of other MutT-related proteins in human cancers remains unknown. The present study systematically investigated the expression of MTH1, MTH2, MTH3 and NUDT5 in human colorectal cancer to establish its clinical significance.

Methods

Amounts of MutT-related mRNA and protein in CRC cell lines were assessed by qRT-PCR and Western blotting, respectively. Furthermore, the MutT-related protein expression was evaluated by immunohistochemical staining of tissue microarrays containing 87 paired CRC tissues and by Western blotting of 44 CRC tissue samples. Finally, the effect of knockdown of MutT-related proteins on CRC cell proliferation was investigated.

Results

The expression of MTH1, MTH2, MTH3 and NUDT5 was significantly higher in CRC cells and CRC tissues than normal cells and tissues, and this phenomenon was significantly associated with AJCC stage and lymph node metastasis of CRC specimens. CRC patients with high expression of MTH1, MTH2 or NUDT5 had an extremely poor overall survival after surgical resection. Notably, NUDT5 was an independent prognostic factor of CRC patients. We found that knockdown of MutT-related proteins inhibited CRC cell proliferation.

Conclusions

We showed for the first time that MutT-related proteins play an important role in CRC progression and prognosis. Further investigations are needed to elucidate the role of these proteins in CRC progression and their potential use for therapeutic targets.

Association of MTH1 expression with the tumor malignant potential and poor prognosis in patients with resected lung cancer

OBJECTIVES

The oxidized purine nucleoside triphosphatase, mutT homolog 1 (MTH1), physiologically sanitizes 8-oxo-dGTP in the nucleotide pool. Previous studies indicated that MTH1 is associated with tumor proliferation and invasion in non-small cell lung cancer (NSCLC) cell lines; however, the role of MTH1 in patients with NSCLC remains unclear.

MATERIALS AND METHODS

Two patient cohorts that underwent surgery for NSCLC in our institution were investigated retrospectively. In one cohort consisting of 197 patients, the associations between MTH1 expression and clinicopathological factors or prognosis were analyzed. In another cohort consisting of 41 patients, the relationship between MTH1 expression in the tumors and serum oxidative stress levels (evaluated by the diacron-reactive oxygen metabolites [d-ROMs] test) or antioxidant capacity in the patients (evaluated by the biological antioxidant potential (BAP) test) was analyzed. A total of 238 patients were assessed for MTH1 protein levels using immunohistochemistry.

RESULTS

Among the 197 patients in the former cohort, 111 (56.3%) exhibited high MTH1 expression, while 86 (43.7%) exhibited low MTH1 expression. Male sex, smoking habit of ≥20 pack-years, squamous cell carcinoma, pathological stage ≥ II, tumor diameter ≥30mm, lymph node metastases, pleural invasion, lymphatic permeation and vascular infiltration were significantly associated with high MTH1 expression (p<0.05). The high MTH1 expression group had a significantly worse prognosis than that of the low MTH1 expression group (5-year overall survival: 81.6% vs. 92.3%, p=0.0011; 5-year disease-free survival: 55.0% vs. 83.7%, p=0.0002). d-ROMs and BAP test values were significantly higher in the high than in the low MTH1 expression group (p<0.05).

CONCLUSION

This study showed that MTH1 protein expression was closely related to factors associated with a high malignant potential and poor patient survival. MTH1 may be a novel therapeutic target for NSCLC.

Prognostic impact of MutT homolog-1 expression on esophageal squamous cell carcinoma

MutT homolog‐1 (MTH1) is a pyrophosphatase that acts on oxidized nucleotides and hydrolyzes 8‐oxo‐2’‐deoxyguanosine triphosphate in deoxynucleoside triphosphate pool to prevent its incorporation into nuclear and mitochondrial DNA, result in reduce cytotoxicity in tumor cells. MTH1 is overexpressed in various cancers and is considered as a therapeutic target. Environmental factors such as cigarette smoking and alcohol consumption are critical risk factors for the development and progression of esophageal squamous cell carcinoma (ESCC), suggesting that oxidative stress contributes to the pathogenesis of ESCC. We examined the expression of MTH1 and the accumulation of 8‐oxo‐2’‐deoxyguanosine (8‐oxo‐dG) in 84 patients with ESCC who underwent curative resection without neoadjuvant therapy. MTH1 mRNA level was quantified by performing quantitative reverse transcription‐PCR. Immunohistochemical analysis of paraffin‐embedded cancer tissues was performed to determine MTH1 protein expression and 8‐oxo‐dG accumulation. MTH1 mRNA expression was higher in cancerous tissues than in the corresponding normal epithelium (P < 0.0001). Immunohistochemical analysis showed that high MTH1 expression was significantly associated with deeper tumor invasion and venous invasion, advanced cancer stage, and poor overall survival (P = 0.0021) and disease‐specific survival (P = 0.0013) compared with low MTH1 expression. Furthermore, high MTH1 expression was an independent predictor of poor disease‐specific survival (P = 0.0121). In contrast, 8‐oxo‐dG accumulation was not associated with any clinicopathological factor and poor prognosis. These results suggest that MTH1 overexpression is a predictor of ESCC progression and poor prognosis and that MTH1 can serve as a therapeutic target for treating patients with ESCC.