The adenosine analog prodrug ATV006 is orally bioavailable and has preclinical efficacy against parental SARS-CoV-2 and variants.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus driving the ongoing coronavirus disease 2019 (COVID-19) pandemic, continues to rapidly evolve. Because of the limited efficacy of vaccination in prevention of SARS-CoV-2 transmission and continuous emergence of variants of concern (VOCs), orally bioavailable and broadly efficacious antiviral drugs are urgently needed. Previously, we showed that the parent nucleoside of remdesivir, GS-441524, has potent anti-SARS-CoV-2 activity. Here, we report that esterification of the 5'-hydroxyl moieties of GS-441524 markedly improved antiviral potency. This 5'-hydroxyl-isobutyryl prodrug, ATV006, demonstrated excellent oral bioavailability in rats and cynomolgus monkeys and exhibited potent antiviral efficacy against different SARS-CoV-2 VOCs in vitro and in three mouse models. Oral administration of ATV006 reduced viral loads and alleviated lung damage when administered prophylactically and therapeutically to K18-hACE2 mice challenged with the Delta variant of SARS-CoV-2. These data indicate that ATV006 represents a promising oral antiviral drug candidate for SARS-CoV-2.

Effect of Rhodotorula mucilaginosa on patulin degradation and toxicity of degradation products.

Rhodotorula mucilaginosa is an antagonistic yeast for which our research team has recently reported interesting biocontrol activities against blue mould decay of apples and a strong ability to decrease the patulin concentration in vivo. However, the possible mechanisms of patulin degradation by R. mucilaginosa and the toxicity of patulin degradation products remain unclear. In this study, the effect of R. mucilaginosa on patulin degradation and toxicity of degradation products were investigated, the results showed that viable cells of R. mucilaginosa are essential to patulin degradation. Also, R. mucilaginosa eliminated patulin without adsorbing it through its cell wall. The extracellular metabolites of R. mucilaginosa stimulated by patulin showed little degradation activity for patulin. Cycloheximide addition into the medium significantly decreased the patulin degradation capacity of R. mucilaginosa cells. The main patulin degradation product by R. mucilaginosa was ascladiol, which was proved non-toxic to human hepatoma (HepG2) cells at 0.625-10 g/mL. Furthermore, toxicological analysis using a confocal laser scanning microscope revealed that the degradation product induced cellular apoptosis to a lesser extent than patulin itself. This result offers an innovative method to detoxify patulin and limit the risks of patulin in fruits and vegetables using R. mucilaginosa.

Regulating the Golgi apparatus sorting of proteinase A to decrease its excretion in Saccharomyces cerevisiae.

Beer foam stability, a key factor in evaluating overall beer quality, is influenced by proteinase A (PrA). Actin-severing protein cofilin and Golgi apparatus-localized Ca2+ ATPase Pmr1 are involved in protein sorting at the trans-Golgi network (TGN) in yeast Curwin et al. (Mol Biol Cell 23:2327-2338, 2012). To reduce PrA excretion into the beer fermentation broth, we regulated the Golgi apparatus sorting of PrA, thereby facilitating the delivery of more PrA to the vacuoles in the yeast cells. In the present study, the cofilin-coding gene COF1 and the Pmr1-coding gene PMR1 were overexpressed in the parental strain W303-1A and designated as W + COF1 and W + PMR1, respectively. The relative expression levels of COF1 in W + COF1 and PMR1 in W + PMR1 were 5.26- and 19.76-fold higher than those in the parental strain. After increases in the expression levels of cofilin and Pmr1 were confirmed, the PrA activities in the wort broth fermented with W + COF1, W + PMR1, and W303-1A were measured. Results showed that the extracellular PrA activities of W + COF1 and W + PMR1 were decreased by 9.24% and 13.83%, respectively, at the end of the main fermentation compared with that of W303-1A. Meanwhile, no apparent differences were found on the fermentation performance of recombinant and parental strains. The research uncovers an effective strategy for decreasing PrA excretion in Saccharomyces cerevisiae.

Discovering the role of the apolipoprotein gene and the genes in the putative pullulan biosynthesis pathway on the synthesis of pullulan, heavy oil and melanin in Aureobasidium pullulans.

Pullulan produced by Aureobasidium pullulans presents various applications in food manufacturing and pharmaceutical industry. However, the pullulan biosynthesis mechanism remains unclear. This work proposed a pathway suggesting that heavy oil and melanin may correlate with pullulan production. The effects of overexpression or deletion of genes encoding apolipoprotein, UDPG-pyrophosphorylase, glucosyltransferase, and α-phosphoglucose mutase on the production of pullulan, heavy oil, and melanin were examined. Pullulan production increased by 16.93 and 8.52% with the overexpression of UDPG-pyrophosphorylase and apolipoprotein genes, respectively. Nevertheless, the overexpression or deletion of other genes exerted little effect on pullulan biosynthesis. Heavy oil production increased by 146.30, 64.81, and 33.33% with the overexpression of UDPG-pyrophosphorylase, α-phosphoglucose mutase, and apolipoprotein genes, respectively. Furthermore, the syntheses of pullulan, heavy oil, and melanin can compete with one another. This work may provide new guidance to improve the production of pullulan, heavy oil, and melanin through genetic approach.