Development of a simple in vitro assay to identify and evaluate nucleotide analogs against SARS-CoV-2 RNA-dependent RNA polymerase

Nucleotide analogs targeting viral RNA polymerase have been approved to be an effective strategy for antiviral treatment and are attracting antiviral drugs to combat the current SARS-CoV-2 pandemic. In this report, we develop a robust in vitro nonradioactive primer extension assay to evaluate the incorporation efficiency of nucleotide analog by SARS-CoV-2 RNA-dependent RNA polymerase (RdRp) quantitively. Our results show that many nucleotide analogs can be incorporated into RNA by SARS-CoV-2 RdRp, and that the incorporation of some of them leads to chain termination. The discrimination values of nucleotide analog over those of natural nucleotide were measured to evaluate the incorporation efficiency of nucleotide analog by RdRp. We found that the incorporation efficiency of Remdesivir-TP is higher than ATP, and we did not observe chain termination or delayed chain termination caused by single Remdesivir-TP incorporation, while multiple incorporations of Remdesivir-TP caused chain termination in our assay condition. The incorporation efficiency of Ribavirin-TP and Favipiravir-TP is very low either as ATP or GTP analogs, which suggested that mutagenesis may not be the mechanism of action of those two drugs against SARS-CoV-2. Incorporation of Sofosbuvir-TP is also very low suggesting that sofosbuvir may not be very effective in treating SARS-CoV-2 infection. As a comparison, 2-C-Methyl-GTP can be incorporated into RNA efficiently, and the derivative of 2-C-Methyl-GTP may have therapeutic application in treating SARS-CoV-2 infection. This report provides a simple screening method that should be useful in evaluating nucleotide-based drugs targeting SARS-CoV-2 RdRp, and for studying the mechanism of action of selected nucleotide analog.

Screening different HPV genotypes infection and type-specific in cervical exfoliated cells of women in Yili area of Xinjiang Uygur Autonomous Region, China / 中华预防医学杂志

Objective@#To investigate the infection status and genotype distribution of cervical human papillomavirus (HPV) in women of different ethnic groups and different ages in Yili, Xinjiang Uygur Autonomous Region (Xinjiang).@*Methods@#By using the convenient sampling method, 54 760 women from November 2015 to May 2017 seeking for service in gynecological clinics in a general hospital in Yili, Xinjiang, were selected as the research subjects, and 3 445 samples of cervical mucous exfoliative cells were collected, and the social information of their ethnic and age was collected at the same time. The inclusion criteria were those with sexual life, cervical integrity, and ethnic groups for Han or Uygur or Kazak. PCR-reverse dot blot hybridization was used to detect HPV genotyping in exfoliated cells, and chi-square test was used to compare the difference of HPV positive rate among different ethnic groups. Then, according to ethnicity and age, the differences in positive rates of different ages and ethnic groups were compared in each layer.@*Results@#The positive rate of HPV was 25.6% (882 cases), of which the Han, Uygur and Kazakh were 27.9% (564 cases), 22.9% (196 cases) and 21.6% (122 cases), and the difference was statistically significant (χ2=13.80, P=0.001). The most prevalent high-risk genotypes of Han women were HPV16/52/58, accounting for 24.8% (140 cases), 17.7% (100 cases) and 9.8% (55 cases), respectively. The most prevalent high-risk genotypes of Uygur women were HPV16/52/53, accounting for 34.2% (67 cases), 12.8% (25 cases), 9.2% (18 cases), respectively. The most prevalent high-risk genotypes of Kazak were HPV16/52/53, accounting for 37.7% (46 cases), 17.2% (21 cases), 12.3% (15 cases), respectively. The highest rate of HPV in Uygur patients aged ≥61 years was 41.5% (22 cases), and the lowest in group 36-40 years old, 15.9% (21 cases), the difference between different age groups was statistically significant (χ2=35.01, P<0.001).@*Conclusion@#The positive rate of HPV infection among Han, Uygur and Kazak in Yili Prefecture of Xinjiang was different, and the HPV positive genotype differs among different ethnic groups.

Comparison of cellular localization of NS1 from different subtypes of influenza A virus / 生物工程学报

The non-structural (NS1) protein is a multifunctional molecular protein encoded by influenza A virus genome. NS1 plays an important role in inhibition of host immune responses. In order to assess the cellular localization of NS1 in different influenza A virus subtypes, we performed the immunofluorescence assay to observe the cellular location of NS1 after infection with influenza A virus WSN (H1N1), PR8 (H1N1), CA04 (H1N1), SD (H9N2) and AH01 (H7N9) in A549 cells and MDCK cells respectively. According to the results, NS1-WSN and NS1-PR8 accumulated mainly in cytoplasm at 24 h post infection, while the NS1-CA04 and NS1-SD appeared major in the nucleus. We also observed localization of NS1 by transfected 293T cells with plasmids which encoding the full-length NS1 from WSN, SD and AH01. The key sites which might determine the different cellular localization of NS1 were chosen by sequence alignment, and seven residues which were different between WSN, PR8 and CA04, SD and AH01 were finally focused. However, we found that single mutation of these residues could not alter the localization of NS1. The data indicated that the difference of location might not be caused by substitution of a single site, which contributes to our understanding of the diverse regulation of host factors during different subtypes of influenza virus infection.