The severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel phlebovirus, recently being officially renamed as Dabie bandavirus, and a causative agent for an emerging infectious disease associated with high fatality. Effective therapeutics and vaccines are lacking and disease pathogenesis is yet to be fully elucidated. In our effort to identify new SFTSV inhibitory molecules, 6-Thioguanine (6-TG) was found to potently inhibit SFTSV infection. 6-TG has been widely used as therapeutic agent since the approval of the Food and Drug Administration in the 1960s. In the current study, we showed that 6-TG was a potent inhibitor of SFTSV infection with 50% effective concentrations (EC50) of 3.465 μM in VeroE6 cells, and 1.848 μM in HUVEC cells. The selectivity index (SI) was >57 in VeroE6 cells and >108 in HUVEC cells, respectively. The SFTSV RNA transcription, protein synthesis, and progeny virions were reduced in a dose dependent manner by the presence of 6-TG in the in vitro infection assay. Further study on the mechanism of the anti-SFTSV activity showed that 6-TG downregulated the production of early growth response gene-1 (EGR1). Using gene silencing and overexpression, we further confirmed that EGR1 was a host restriction factor against SFTSV. Meanwhile, treatment of infected experimental animals with 6-TG inhibited SFTSV infection and alleviated multi-organ dysfunction. In conclusion, we have identified 6-TG as an effective inhibitor of SFTSV replication via the inhibition of EGR1 expression. Further studies are needed to evaluate of 6-TG as a potential therapeutic for treating SFTS.

BACKGROUND: Thiopurine-induced leucopenia significantly hinders the wide application of thiopurines. Dose optimization guided by nudix hydrolase 15 (NUDT15) has significantly reduced the early leucopenia rate, but there are no definitive biomarkers for late risk leucopenia prediction.
OBJECTIVE: To determine the predictive value of early monitoring of DNA-thioguanine (DNATG) or 6-thioguanine nucleotides (6TGN) for late leucopenia under a NUDT15-guided thiopurine dosing strategy in patients with Crohn\'s disease (CD).
METHODS: Blood samples were collected within two months after thiopurine initiation for detection of metabolite concentrations. Late leucopenia was defined as a leukocyte count < 3.5 × 109/L over two months.
RESULTS: Of 148 patients studied, late leucopenia was observed in 15.6% (17/109) of NUDT15/thiopurine methyltransferase (TPMT) normal and 64.1% (25/39) of intermediate metabolizers. In patients suffering late leucopenia, early DNATG levels were significantly higher than in those who did not develop late leucopenia (P = 4.9 × 10-13). The DNATG threshold of 319.43 fmol/μg DNA could predict late leucopenia in the entire sample with an area under the curve (AUC) of 0.855 (sensitivity 83%, specificity 81%), and in NUDT15/TPMT normal metabolizers, the predictive performance of a threshold of 315.72 fmol/μg DNA was much more remarkable with an AUC of 0.902 (sensitivity 88%, specificity 85%). 6TGN had a relatively poor correlation with late leucopenia whether in the entire sample (P = 0.021) or NUDT15/TPMT normal or intermediate metabolizers (P = 0.018, P = 0.55, respectively).
CONCLUSIONS: Proactive therapeutic drug monitoring of DNATG could be an effective strategy to prevent late leucopenia in both NUDT15/TPMT normal and intermediate metabolizers with CD, especially the former.

6-Thioguanine (6-TG) is a purine analog anticancer drug used to treat childhood acute leukemia and inflammatory bowel disease; however, the over-dosage use of 6-TG can cause serious adverse effects. Therefore, monitoring the free 6-TG concentration in the human body is critical during drug therapy. In this work, a highly sensitive and rapid fluorescent nanoprobe based on Cu/Ag nanoclusters (NCs) for the detection of 6-TG was developed. The maximum emission wavelength of Cu/Ag NCs was observed at 563 nm with an excitation wavelength of 330 nm. A selective fluorescence quenching effect of 6-TG on the Cu/Ag NCs was found. Under optimum conditions for the determination of 6-TG, a wide linear concentration range from 2.5 to 100 μmol L-1 was observed with a limit of detection (LOD) of 1.57 μmol L-1. The characteristics of simple operation, high sensitivity and selectivity make this fluorescent nanoprobe a promising candidate for the detection of 6-TG in biological samples, as demonstrated by the application in spiked human serum with recoveries of 97.6 to 104.8%. In general, this proposed method has good potential for the detection of 6-TG in biological samples.

In present work, a novel voltammetric sensor for the determination of 6-thioguanine (6-TG) was fabricated. First, a graphite rod electrode (GRE) surface was modified via drop-coating of graphene oxide (GO) to increase the surface area of the electrode. Subsequently, molecularly imprinted polymer (MIP) network was prepared using a facile electro-polymerization procedure, using o-aminophenol (as functional monomer) and 6-TG (as template molecule). Influences of test solution pH, dropped GO concentration and incubation time on the performance of GRE-GO/MIP were studied, and their values determined as 7.0, 1.0 mg/mL and 90 s, respectively. Using GRE-GO/MIP, 6-TG was measured in the range of 0.5-60 μM with a low detection limit (DL) of 80 nM (based on S/N = 3). In addition, the electrochemical device demonstrated good reproducibility (3.8%) and anti-interference ability toward 6-TG monitoring. The as-prepared sensor illustrated satisfactory sensing performance in real samples with recovery ranging from 96.5% to 102.5%. For the determination of trace amounts of anticancer drug (6-TG) in real matrices (biological samples and pharmaceutical wastewater sample), this study is expected to provide an effective strategy with high selectivity, stability, and sensitivity.

The development of accurate and sensitive detection methods of anticancer drugs is of significant importance because they play vital roles in biological systems. In recent years, bimetallic nanoclusters (BMNCs) incorporating the advantages of two metals have gained more and more attention, and can be widely applied in sensing applications. In this work, for the first time, we designed a sensing platform based on terbium ion (Tb3+) triggered aggregation-induced emission (AIE) of BMNCs. Tb3+ hybrid glutathione (GS) protected Ag/Cu nanoclusters (Tb3+@GS-AgCuNCs) were facilely fabricated according to the complexation reaction between Tb3+ and the carboxyl group of GS. Due to the inner filter effect (IFE), the fluorescence of Tb3+@GS-AgCuNCs decreased significantly in the presence of anticancer drugs with 6-thioguanine and methotrexate as representatives. In addition, the sensing platform was applied to monitor 6-thioguanine and methotrexate in real serum samples, indicating that it has great potential in anticancer drugs related applications.

Thiopurine dose optimization by thiopurine-S-methyltransferase (TPMT) or nudix hydrolase-15 (NUDT15) significantly reduced early leucopenia in Asia. However, it fails to avoid the late incidence (> 2 months). Although laboratory monitoring of 6-thioguanine nucleotides (6TGN) to optimize thiopurine dose was suggested in White patients the exact association between leucopenia and 6TGN was controversial in Asian patients. In the present study, we aimed to explore whether DNA-thioguanine nucleotides (DNA-TGs) in leukocytes, compared with 6TGN in erythrocytes, can be a better biomarker for late leucopenia. This was a prospective, observational study. Patients with inflammatory bowel disease (IBD) prescribed thiopurine from February 2019 to December 2019 were recruited. Thiopurine dose was optimized by NUDT15 C415T (rs116855232). DNA-TG and 6TGN levels were determined at the time of late leucopenia or 2 months after the stable dose was obtained. A total of 308 patients were included. Thiopurine induced late leucopenia (white blood cells < 3.5 × 109 /L) were observed in 43 patients (14.0%), who had significantly higher DNA-TG concentration than those without leucopenia (P = 4.1 × 10-9 , 423.3 (~ 342.2 to 565.7) vs. 270.5 (~ 188.1 to 394.3) fmol/μg DNA). No difference in 6TGN concentrations between leucopenia and non-leucopenia was found. With a DNA-TG threshold of 340.1 fmol/μg DNA, 83.7% of leucopenia cases could be identified. Multivariate analysis showed that DNA-TG was an independent risk factor for late leucopenia. Quantification of DNA-TG, rather than 6TGN, can be applied to gauge thiopurine therapy after NUDT15 screening in Chinese patients with IBD.

Though various therapeutic strategies have been developed to overcome gastric cancer, the overall prognosis and therapeutic effect are still not optimistic. As a novel identified type of cell death, ferroptosis has been considered as a promising tumor suppression mechanism with therapeutic potential against gastric cancer. In this work, we screened a collection of 4890 bioactivity compounds and committed to find novel agents that can induce apoptosis in gastric cancer. Among these compounds, 6-TG was identified as a potential ferroptosis inducer in gastric cancer cells for the first time. It could inactivate system xc-, block the generation of GSH, down-regulate the expression of GPX4, increase the level of lipid ROS, and finally trigger the Fe2+-mediated ferroptosis in MGC-803 and AGS cell lines. The date in vivo also suggested that compound 6-TG performed anti-tumor activity via inducing ferroptosis. These findings gave a support for 6-TG may play as a novel leading compound for gastric cancer treatment as a ferroptosis inducer.

The nucleobase analog 6-thioguanine (6-TG) has emerged as important immunosuppressant, anti-inflammatory, and anticancer drug in the past few decades, but its unique photosensitivity of absorbing strongly ultraviolet UVA light elicits photochemical hazards in many ways. The particularly intriguing yet unresolved question is whether the direct photoreaction of 6-TG can promote DNA-protein cross-links (DPCs) formation, which are large DNA adducts blocking DNA replication and physically impede DNA-related processes. Herein, by real-time observation of radical intermediates using time-resolved UV-vis absorption spectroscopy in conjunction with product analysis by HPLC-MS, we discover that UVA excitation of 6-TG triggers direct covalent cross-linking with tryptophan (TrpH) via an exquisite radical mechanism of electron transfer. The photoexcitation prepares the redox-active triplet 36-TG*, which initiates electron transfer with TrpH, creating TrpH•+ and 6-TG•- in the first step. The deprotonated Trp• undergoes radical-recombination with its geminate partner 6-TG•- and eliminates a H2S, leading to the cross-linking product 6-TG-Trp. The photoadduct structures (two chiral isomers and one constitutional isomer) are identified unambiguously, validating further the mechanism. These findings pinpoint the exact amino acid that is vulnerable to photo-cross-linking with 6-TG and establish a mechanistic framework for understanding mutagenic DPCs formation and developing photoprobes based on this new type of photo-cross-linking.

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Triple-negative breast cancer (TNBC) is notoriously difficult to treat due to the lack of biological targets and poor sensitivity to conventional therapies. Chemotherapy is the main clinical therapy, but the effective screening strategy for chemotherapy drugs is poorly investigated. Drug repositioning has been the center of attention in recent years attracting numerous studies. Here, we firstly found multiple common features between leukemia and TNBC by analyzing the global transcriptome profiles based on the transformed comparison data from NCI60. Therefore, we investigated the role of the classic leukemia drug thioguanine (6-TG) in TNBC cancer cells. Our results indicated that 6-TG inhibited cell proliferation and tumor cell progression by suppressing PI3K-AKT pathway via downregulating the DNA methylation level of PTEN. Moreover, apoptosis was induced via the activation of PI3K-AKT downstream TSC1 and the downregulation of methylation levels of DAXX, TNF, FADD and CASP8 etc. These findings indicated 6-TG exerts its anti-tumor effects in vitro and in vivo through regulating the DNA methylation levels of genes involved in PI3K-AKT and apoptosis pathway. Meanwhile, our study suggested that transcriptome-based drug screening has potential implications for breast cancer therapy and drug selection.