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

Abstract

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.

Nucleoside analog GS‐441524: pharmacokinetics in different species, safety, and potential effectiveness against Covid‐19

“…Previously, we suggested that endogenous https://www.guidetopharmacology.org/GRAC/LigandDisplayForward?ligandId=2844 competes with GS‐441524 for cellular uptake by nucleoside transporters such as equilibrative nucleoside transporter 1, and the perceived rate‐limiting first step of its phosphorylation to GS‐441524 monophosphate eventually leading to the formation of GS‐441524 triphosphate 11 . Under physiological conditions, extracellular and intracellular adenosine levels are in the submicromolar range, but these levels are significantly elevated in hypoxia and critical illness, occasionally being increased by 5‐ to 10‐fold or more, e.g.…”

“…Since GS‐441524 is a nucleoside analog lacking the McGuigan moiety characteristic of ProTides, its pharmacokinetics (PK) differs markedly from that of remdesivir. Notably, cellular uptake of GS‐441524 is believed to be dependent upon membrane‐bound transporters since it is hydrophilic with limited ability to cross cell membranes by diffusion 11 . By contrast, uptake of remdesivir appears to be mediated by diffusion, which is facilitated by its hydrophobic prodrug moieties, thus probably to a large extent being independent of membrane‐bound transporters 5,6,12 .…”

“…Notably, cellular uptake of GS‐441524 is believed to be dependent upon membrane‐bound transporters since it is hydrophilic with limited ability to cross cell membranes by diffusion. 11 By contrast, uptake of remdesivir appears to be mediated by diffusion, which is facilitated by its hydrophobic prodrug moieties, thus probably to a large extent being independent of membrane‐bound transporters. 5 , 6 , 12 Once inside the cells, the GS‐441524 is phosphorylated to the active antiviral GS‐441524 triphosphate metabolite, also known as GS‐443902, with adenosine kinase probably being responsible for catalyzing the first and perceived rate‐limiting step in the formation of this metabolite.…”

Preclinical Pharmacokinetics and In Vitro Properties of GS-441524, a Potential Oral Drug Candidate for COVID-19 Treatment

“…GS-441524 is reported to be an effective treatment of feline infectious peritonitis (FIP) caused by feline coronavirus ( Dickinson et al, 2020 ). The cellular uptake and phosphorylation of GS-441524 ( Rasmussen et al, 2021 ), PK of ester prodrugs of GS-441524 in mice ( Wei et al, 2021 ), and the in vivo efficacy in a SARS-CoV-2 mouse model ( Li et al, 2021 ) of GS-441524 have been reported recently. In addition, PK and efficacy of a triester prodrug of GS-441524 in mouse and ferret models of SARS-CoV-2 infection have been reported ( Cox et al, 2021 ; Schafer et al, 2021 ).…”

Preclinical Pharmacokinetics andIn VitroProperties of GS-441524, A Potential Oral Drug Candidate for COVID-19 Treatment

“…GS-441524 is reported to be an effective treatment of feline infectious peritonitis (FIP) caused by feline coronavirus [10]. The cellular uptake and phosphorylation of GS-441524 [11], PK of ester prodrugs of GS-441524 in mice [12], and the in vivo efficacy in a SARS-CoV-2 mouse model [13] of GS-441524 have been reported recently. In addition, PK and efficacy of a triester prodrug of GS-441524 in mouse and ferret models of SARS-CoV-2 infection have been reported [14, 15].…”