4.3. NSAIDs: Indomethacin (Indocin) and Naproxen (Aleve)
In one hand, indomethacin is a synthetic, small molecule of N-benzoyl-indole-3-acetic acid derivative (Figure 7). It was first approved by the U.S. FDA in 1984 for use as NSAID. It also possesses analgesic and antipyretic properties. It is used for acute mild to moderate pain. It is also used for ankylosing spondylitis, bursitis, tendonitis, osteoarthritis, and rheumatoid arthritis, among other conditions. The known mechanism is the reversible inhibition of cyclooxygenase-1 and 2 enzymes, which leads to decreased formation of prostaglandin precursors [142]. Orally administered indomethacin is being evaluated in combination with hydroxychloroquine and azithromycin in an open-label, single-arm, phase 2 study to determine its efficacy and safety in subjects with mild COVID-19 symptoms (NCT04344457; n = 80).
Considering activity against coronaviruses, in vitro studies demonstrated that indomethacin has a potent direct antiviral activity against the SARS coronavirus as determined in monkey Vero E6 cells and human lung epithelial A549 cells as well as against the canine coronavirus as determined in A72 canine cells. Indomethacin blocked the viral RNA synthesis, but not the viral adhesion/entry into the host cells. This effect is independent of the cyclooxygenase inhibition. At a dose rate of 1 mg/kg, indomethacin resulted in more than 1000-fold reduction in the virus yield in coronavirus-infected dogs [143]. Likewise, indomethacin has been reported to be a potent inhibitor of SARS CoV-2 replication in Vero E6 cells with an IC50 value of 1 µM, which is 10-fold less than its peak plasma concentration, and a selective index of 500-fold. Using a dose of 1 mg/kg in canine coronavirus-infected dogs, indomethacin accelerated the symptoms relieve and saved all infected animals, relative to ribavirin or anti-canine coronavirus serum/canine hemoglobin/canine blood immunoglobulin/INF regimen [144]. Previously, indomethacin also showed antiviral activity against rotavirus infection and vesicular stomatitis virus infection [145,146]. The antiviral activity of indomethacin was proposed to be a result of its binding to peroxisome proliferator activated receptor-γ, aldose reductase, and/or the viral NSP7/NSP8 complex [144]. The inhibition of the NSP7/NSP8 complex has been relatively verified and happened by indomethacin potentially targeting the interface between the host prostaglandin E synthase 2 and the viral NSP7/NSP8. In fact, prostaglandin E synthase 2 itself is inhibited by indomethacin in Vero cells with an IC50 value of 750 nM [144]. Lastly, in addition to the inhibition of the pro-inflammatory prostaglandin biosynthesis, indomethacin was also found to halt the increase in IL-6 expression caused by lipopolysaccharide-treated U937 cells [147]. Accordingly, the effect of indomethacin on IL-6 may translate into beneficial effect in treating the cytokine storm of COVID-19.
In the other hand, naproxen is another synthetic, small molecule NSAID that is a derivative of 2-naphthalene-acetic acid (Figure 7). It was first approved by the U.S. FDA in 1976 for oral use in the treatment of a host of painful inflammatory conditions such as ankylosing spondylitis, bursitis, polyarticular juvenile idiopathic arthritis, osteoarthritis, rheumatoid arthritis, tendonitis, dysmenorrhea pain, and gout [148,149]. The efficacy of naproxen in the treatment of critically ill, hospitalized COVID-19 patients is being evaluated in a randomized, open label clinical trial (NCT04325633; n = 584).
The drug has been reported to exhibit antiviral activity against influenza A and B viruses with IC50 values in the low micromolar range. In this arena, naproxen antagonized CRM1-mediated nuclear export of proteins of influenza A and B viruses. Naproxen also provided therapeutic protection to mice infected with influenza B virus [150,151]. In hospitalized patients with influenza, it was found that adding clarithromycin and naproxen to oseltamivir shortened the hospitalization time [150,151]. Naproxen also inhibited the replication of Zika virus by reducing the expression of AXL, the entry cofactor of Zika virus [152]. Naproxen’s antiviral activity against SARS-CoV-2 has also been proposed by a recent computational work and has been attributed its ability to bind to the viral nucleocapsid protein. In fact, it was recently reported that naproxen inhibits SARS-CoV-2 infection in Vero E6 cells and in reconstituted human airway epithelia with IC50 values comparable to those effective in influenza [153]. Lastly, similar to indomethacin, the anti-inflammatory effects of naproxen may also translate into beneficial effects in treating the cytokine storm of COVID-19.