Ribonucleotide reductase ( RR ) is a rate-limiting enzyme, and it is responsible for reducing ribonucleotides to their corresponding deoxyribonucleotides , which are the building blocks required for DNA replication and repair .Recent studies have revealed that RR activity is associated with DNA replication in virus , and RR inhibitors have been used for clinical antiviral treatment .This paper reviews research progress on RR and its inhibitors , including the classification , structure and function of RR; the classification, mechanism and clinical application of RR inhibitors in antiviral therapy and the future prospects of RR inhibitors .

Drugs targeting immune checkpoint are used for cancer treatment, but resistance to single drug may occur. Combination therapy blocking multiple checkpoints simultaneously can improve clinical outcome. Therefore, we designed a recombinant protein rPC to block multiple targets, which consists of extracellular domains of programmed cell death protein 1 (PD-1) and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4). The coding sequence was inserted into expression vector and stably transfected into HEK293 cells. The culture supernatant was collected and rPC was affinity-purified. Real-time quantitative PCR was used to evaluate the expression levels of ligands for PD-1 and CTLA-4 in several human cancer cell lines. The binding of rPC with cancer cells was examined by immunofluorescence cell staining, the influence of rPC on cancer cell growth was assayed by CCK-8. The results showed that rPC could be expressed and secreted by stably transfected HEK293 cells, the purified rPC could bind to lung cancer NCI-H226 cells which have high levels of ligands for PD-1 and CTLA-4, no direct impact on cancer cell growth could be observed by rPC treatment. The recombinant protein rPC can be functionally assayed further for developing novel immunotherapeutic drugs for cancer.
Animals ; CTLA-4 Antigen ; genetics ; Cell Proliferation ; HEK293 Cells ; Humans ; Lung Neoplasms ; metabolism ; Programmed Cell Death 1 Receptor ; genetics ; Protein Binding ; Protein Domains ; genetics ; Recombinant Fusion Proteins ; genetics ; isolation & purification ; metabolism

OBJECTIVE To explore the mechanism of action of epigallocatechin-3-gallate(EGCG) in inhibiting laryngeal cancer cells. METHODS The expression of epidermal growth factor receptor(EGFR) in laryngeal cancer cell lines AMC-HN-8, TU686 and TU212 was detected by Western blotting, and the inhibitory effects of cetuximab and EGCG on three laryngeal cancer cells were detected by CCK-8 assay. A lentiviral vector containing EGFR promoter and Luc reporter gene was constructed to generate a TU686-EGFR-Luc cell line that could steadily express Luc activity. Luciferase assay was performed to evaluate the effect of EGCG on the transcription activity of EGFR promoter. Cell cycle and apoptosis of EGCG-treated laryngeal carcinoma cells were analyzed by flow cytometry, and changes of the levels of EGFR and downstream ERK1/2, cell cycle-associated proteins P53 and P27, apoptosis-associated proteins BCL2 and PART, and autophagy marker LC3A/B were further examined. RESULTS The laryngeal carcinoma cell lines were insensitive to cetuximab but could be effectively suppressed by EGCG. EGCG effectively inhibited the transcription activity of EGFR promoter. Treatment of TU686 cells at sub-IC50 dose EGCG resulted in significant cell cycle arrest at S phase with partial apoptosis. Significant inhibition of expression and activation of EGFR and downstream signaling pathway were observed. CONCLUSION EGCG can effectively downregulate EGFR and suppress laryngeal carcinoma cells, further investigation on in vivo effect and mechanisms are anticipated.