In-cell bioluminescence resonance energy transfer (BRET)-based assay uncovers ceritinib and CA-074 as SARS-CoV-2 papain-like protease inhibitors.

Papain-like protease (PLpro) is an attractive anti-coronavirus target. The development of PLpro inhibitors, however, is hampered by the limitations of the existing PLpro assay and the scarcity of validated active compounds. We developed a novel in-cell PLpro assay based on BRET and used it to evaluate and discover SARS-CoV-2 PLpro inhibitors. The developed assay demonstrated remarkable sensitivity for detecting the reduction of intracellular PLpro activity while presenting high reliability and performance for inhibitor evaluation and high-throughput screening. Using this assay, three protease inhibitors were identified as novel PLpro inhibitors that are structurally disparate from those previously known. Subsequent enzymatic assays and ligand-protein interaction analysis based on molecular docking revealed that ceritinib directly inhibited PLpro, showing high geometric complementarity with the substrate-binding pocket in PLpro, whereas CA-074 methyl ester underwent intracellular hydrolysis, exposing a free carboxyhydroxyl group essential for hydrogen bonding with G266 in the BL2 groove, resulting in PLpro inhibition.

Safety assessment of Wuzhuyu decoction extract: acute and subacute oral toxicity studies in rats.

Wuzhuyu decoction (WZYD) is a well-known classic traditional Chinese medicine prescription and has been widely used to treat headache, nausea, vomiting, insomnia, etc. However, little published information is available about its safety. Our aim was to investigate the acute and subacute oral toxicity of WZYD extract in rats following the technical guidelines from China's National Medical Products Administration (NMPA) for single and repeated doses toxicity studies of drugs. Acute oral toxicity was assessed in rats via oral administration of WZYD extract at 4 g/kg three times within a day followed by a 14-day observation period. To evaluate the subacute toxicity, rats were orally administered with WZYD extract at doses of 0, 0.44, 1.33, and 4 g/kg for 28 days. The items examined included clinical signs, body weight, food consumption, hematological and biochemical parameters, bone marrow smear, organ index, and histopathology. After the rats were administered with 12 g/kg (3 × 4 g/kg) WZYD extract, no mortality and toxic effects were observed during the observation period. In the subacute toxicity study, WZYD extract did not cause any significant treatment-related abnormality in each examined item of rats, so the no observed adverse effect level (NOAEL) of WZYD extract for 28 days orally administered to rats is considered to be 4 g/kg, which is approximately 80-fold of its clinical proposed dosage.