Cellular Uptake and Intracellular Phosphorylation of GS-441524: Implications for Its Effectiveness against COVID-19

GS-441524 is an adenosine analog and the parent nucleoside of the prodrug remdesivir, which has received emergency approval for treatment of COVID-19. Recently, GS-441524 has been proposed to be effective in the treatment of COVID-19, perhaps even being superior to remdesivir for treatment of this disease. Evaluation of the clinical effectiveness of GS-441524 requires understanding of its uptake and intracellular conversion to GS-441524 triphosphate, the active antiviral substance. We here discuss the potential impact of these pharmacokinetic steps of GS-441524 on the formation of its active antiviral substance and effectiveness for treatment of COVID-19. Available protein expression data suggest that several adenosine transporters are expressed at only low levels in the epithelial cells lining the alveoli in the lungs, i.e., the alveolar cells or pneumocytes from healthy lungs. This may limit uptake of GS-441524. Importantly, cellular uptake of GS-441524 may be reduced during hypoxia and inflammation due to decreased expression of adenosine transporters. Similarly, hypoxia and inflammation may lead to reduced expression of adenosine kinase, which is believed to convert GS-441524 to GS-441524 monophosphate, the perceived rate-limiting step in the intracellular formation of GS-441524 triphosphate. Moreover, increases in extracellular and intracellular levels of adenosine, which may occur during critical illnesses, has the potential to competitively decrease cellular uptake and phosphorylation of GS-441524. Taken together, tissue hypoxia and severe inflammation in COVID-19 may lead to reduced uptake and phosphorylation of GS-441524 with lowered therapeutic effectiveness as a potential outcome. Hypoxia may be particularly critical to the ability of GS-441524 to eliminate SARS-CoV-2 from tissues with low basal expression of adenosine transporters, such as alveolar cells. This knowledge may also be relevant to treatments with other antiviral adenosine analogs and anticancer adenosine analogs as well.

Bromhexine Hydrochloride: Potential Approach to Prevent or Treat Early Stage COVID-19

The most critical step during viral infection is when viruses enter the cell. A novel coronavirusSARS-CoV-2 penetrates into alveolar cells through the transmembrane serine proteaseTMPRSS2. Extensive studies show that a clinically approved drug from Japan and South Korea,camostat mesylate inactivates TMPRSS2 in order to prevent the infection. However, these basicstudies have not been translated to “bedside”, and their effectiveness has not been clinicallyconfirmed yet. Here, we describe another potential antiviral substance, commonly used in theclinical practice as a mucolytics – bromhexine hydrochloride. Causing only few mild sideeffects, it may serve as either a new therapeutic strategy during early stages of the disease or apreventive agent blocking SARS-CoV-2 entry into alveolar cells through TMPRSS2.Therefore, in this review, we discuss these possible approaches based on the current data.

Rotavirus Inhibitor and Recovery in Raw Bovine Milk

Milk could be a vector for viruses contaminating the human gut, but detection of rotavirus in raw bovine milk is prevented by the presence of a very active antiviral substance. Rotavirus inhibition by various milk samples and the nature of the inhibitor were examined, and an improved method for rotavirus detection in raw bovine milk was designed. Most milk samples from cows near Toulouse, France, could inhibit 5 × 106 PFU/ml of rotavirus, with wide variations among individuals and with time. The rotavirus inhibitor was bound on a protein G affinity column, and corresponded to the immunoglobulin G fraction (IgG) as shown by enzymatic immunoassay. The proposed method for rotavirus detection requires the action of HCl (pH 3) and dithiothreitol (0.01 M) for 10 min before PFU counts on cell cultures. This treatment improved the detection threshold 1,000-fold, and the recovery of rotavirus in raw bovine milk 300-fold.