Evaluation of mechanisms of action of re-purposed drugs for treatment of COVID-19

Abstract

Coronavirus disease 2019 (COVID-19) is a global health emergency caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). The rapid worldwide spread of SARS-CoV-2 infection has necessitated a global effort to identify effective therapeutic strategies in the absence of vaccine. Among the re-purposed drugs being tested currently, hydroxychloroquine (HCQ), without or with zinc ion (Zn⁺⁺) and the antibiotic azithromycin (AZM), has been administered to prevent or treat patients with COVID-19. The outcome of multiple clinical studies on HCQ has been mixed. Zn⁺⁺ interferes with viral replication by inhibiting replicative enzymes and its entry into cells may be facilitated by HCQ. Another immunomodulatory drug, methotrexate (MTX), is well known for its ability to mitigate overactive immune system by upregulating the anti-inflammatory protein, A20. However, its beneficial effect in treating COVID-19 has not drawn much attention. This review provides an overview of the virology of SARS-CoV-2 and an analysis of the mechanisms by which these anti-inflammatory agents may act in the treatment of COVID-19 patients. We propose a rationale for the combinatorial use of these re-purposed drugs that may help to combat this ongoing pandemic health emergency.

Keywords: COVID-19; Cytokine storm; Hydroxychloroquine; Methotrexate; SARS-CoV-2.

Graphical abstract

Fig. 1

Life cycle of coronavirus. (A) ACE-2-mediated entry of corona virus via endocytosis, followed by uncoating and synthesis of polyprotein 1a (pp1a) and pp1ab using genomic RNA (+ve) strand. Proteolysis of polyproteins with the help of host lysosomal proteases to make nonstructural protein RNA-dependent RNA polymerase (RdRP) that uses (+ve) strand genomic RNA as a template. The (+ve) strand genomic RNA is synthesized by the process of replication becomes the genome of the new virus particles. The transcription of (–ve) strand into subgenomic RNAs that are translated into structural proteins. Reassembly of viral particles in RER and secreted via Golgi vesicles as new viruses by exocytosis.

Fig. 2

Pathogenesis of corona virus and its interference by HCQ and MTX. (A) Phagocytosis of coronavirus by immune cells results in the activation PRR-mediated NF-κB and IRF7 signaling leading to induction of the cytokine storm. HCQ inhibits the engagement of viral nucleotides with endosomal TLRs by increasing pH. MTX inhibits cytokine storm by inducing an anti-inflammatory molecule, A20.

Fig. 3

Possible sites of inhibition of viral replication by combination of HCQ, Zn⁺⁺ and MTX. The combination of HCQ, Zn⁺⁺ and MTX interferes with viral replication at several stages. HCQ interferes directly by inhibiting fusion of virus to host membrane receptors and indirectly acts as ionophore that transports Zn⁺⁺ that inhibits viral RNA polymerase. HCQ directly interacts with sialic acid and interferes in the attachment of virus to membrane glycoproteins. MTX interferes at viral replication stage by depleting the nucleotide pool.

Fig. 4

MTX-mediated A20 upregulation inhibits TNF-α-induced signaling. TLR7/8-mediated TNF-α release from coronavirus-stimulated immune cells acts on lung epithelial cells, induces NF-κB activation, apoptosis and necroptosis that leads to the destruction of lung tissue. MTX-mediated A20 involves in the survival of lung tissue by inhibiting TNF-α-induced NF-κB activation, apoptosis and necroptosis.