Human infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19) and there is no cure currently. The 3CL protease (3CLpro) is a highly conserved protease which is indispensable for CoVs replication, and is a promising target for development of broad-spectrum antiviral drugs. In this study we investigated the anti-SARS-CoV-2 potential of Shuanghuanglian preparation, a Chinese traditional patent medicine with a long history for treating respiratory tract infection in China. We showed that either the oral liquid of Shuanghuanglian, the lyophilized powder of Shuanghuanglian for injection or their bioactive components dose-dependently inhibited SARS-CoV-2 3CLpro as well as the replication of SARS-CoV-2 in Vero E6 cells. Baicalin and baicalein, two ingredients of Shuanghuanglian, were characterized as the first noncovalent, nonpeptidomimetic inhibitors of SARS-CoV-2 3CLpro and exhibited potent antiviral activities in a cell-based system. Remarkably, the binding mode of baicalein with SARS-CoV-2 3CLpro determined by X-ray protein crystallography was distinctly different from those of known 3CLpro inhibitors. Baicalein was productively ensconced in the core of the substrate-binding pocket by interacting with two catalytic residues, the crucial S1/S2 subsites and the oxyanion loop, acting as a “shield” in front of the catalytic dyad to effectively prevent substrate access to the catalytic dyad within the active site. Overall, this study provides an example for exploring the in vitro potency of Chinese traditional patent medicines and effectively identifying bioactive ingredients toward a specific target, and gains evidence supporting the in vivo studies of Shuanghuanglian oral liquid as well as two natural products for COVID-19 treatment.

This work describes the development and investigation of an aptamer modified microfluidic device that captures rare cells to achieve a rapid assay without pre-treatment of cells. To accomplish this, aptamers are first immobilized on the surface of a poly (dimethylsiloxane) microchannel, followed by pumping a mixture of cells through the device. This process permits the use of optical microscopy to measure the cell-surface density from which we calculate the percentage of cells captured as a function of cell and aptamer concentration, flow velocity, and incubation time. This aptamer-based device was demonstrated to capture target cells with > 97% purity and > 80% efficiency. Since the cell capture assay is completed within minutes and requires no pre-treatment of cells, the device promises to play a key role in the early detection and diagnosis of cancer where rare diseased cells can first be enriched and then captured for detection.