Review 2: "Inhibiting Glutamine Metabolism Blocks Coronavirus Replication in Mammalian Cells"

RR:C19 Evidence Scale rating by reviewer:

• Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.

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Review:

This preprint suggests that targeting glutamine metabolism with glutaminase inhibitors may be a promising therapeutic strategy for COVID-19. The study shows that these inhibitors can block viral replication in mammalian epithelial cells and highlights the importance of glutamine metabolism for coronavirus replication in human cells. This research may lead to the development of new anti-viral drugs to combat COVID-19.

Clinically, a meta-analysis highlighted that higher levels of glutamine were linked to a reduced risk of getting infected with SARS-CoV-2 and having a severe case of COVID-19. On the other hand, some studies found that elevated levels of glutamate were linked to an increased risk of SARS-CoV-2 infection and severe COVID-19 (DOI: 10.1002/jmv.28150). These conflicting results indicate that there is still debate on this topic. However, several in vitro studies have been performed to understand the role of glutamine metabolism during SARS-Cov-2 infection. 

A study has found (DOI: 10.1111/jnc.15679) that SARS-CoV-2 infection in astrocytes alters the metabolism of glucose and other carbon sources, leading to an increased dependence on glutamine for energy and biosynthesis. The researchers evidenced this using the mitochondrial glutaminase (GLS) inhibitor, L-6-Diazo-5-oxo-norleucine, and by supplementing the media with glutamine in the absence of glucose. de Oliveira et al., also found that inhibiting glutamine metabolism could reduce viral replication in astrocytes. These findings suggest that targeting glutamine metabolism could be a potential therapeutic strategy for COVID-19.

In another study, Mullen et al. (DOI:10.1038/s41467-021-22166-4) found that SARS-CoV-2 infection rewires host cell metabolism, leading to a decrease in oxidative TCA metabolism of glutamine and an increase in glucose-derived carbon entry into the TCA cycle. The researchers also found that mTORC1 inhibition, which blocks a key pathway in glutamine metabolism, impaired viral replication and inflammatory response in vitro.

Besides the studies previously discussed, there have been additional research efforts exploring the connection between how the body processes glutamine and its association with SARS-CoV-2 infection. In this submitted preprint draft, Greene et al. evidenced that three members of the Coronavirus family, including SARS-CoV-2, require glutamine metabolism for their replication and are susceptible to inhibition by allosteric glutaminase inhibitors. They demonstrated how glutaminase (GLS) inhibitors are especially effective at blocking coronavirus infection and that they may serve as new lead compounds toward the design of even more potent and novel anti-viral drug candidates. The authors also showed that genetic silencing of glutaminase enzymes and small molecule allosteric inhibitors targeting these enzymes can block viral replication in mammalian epithelial cells. They highlighted the importance of glutamine metabolism for coronavirus replication in human cells and suggested that glutaminase inhibitors may represent a novel class of anti-viral drug candidates.

Based on the highlighted results, in this submitted manuscript, the authors have supported previous in vitro studies with a newly developed GLS inhibitor, UP4, as well as others. They also bring the novelty that genetically silencing of GLS reduces coronavirus replication in vitro.