# An Update of Carbazole Treatment Strategies for COVID-19 Infection
## 4 Carbazoles Treatment
### SARS-CoV-2 M-Pro Inhibitors  
As already reported, protease M-pro, also known as chymotrypsin-like protease, (3 CL-pro) is an enzyme that only exists in the virus and not in humans [75; 76]. For this reason, Mpro is an interesting target for the discovery of new antivirals [77]. [PERSON] et al. in 2020 [45] applied a virtual screening (VS) method for checking approved medicines to verify which of them could inhibit this protease. The drugs studied were docked against the structure of the protease involved using docking programs such as Glide, FRED, and AutoDock Vina. Thanks to these studies, drugs were selected, including one with a carbazole structure, carprofen **(1, Figure 1)**, as possible M-pro inhibitors. Carprofen (2-(6-chloro-9\(H\)-carbazol-2 yl) propanoic acid) **(1)** is a selective COX-2 (cyclooxygenase-2) inhibitor. Compound **1**, in the active site of M-pro, makes many interactions, such as hydrophobic interactions, with Gln189 and Met49, \(\pi\)-\(\pi\) interaction with His41 through its ring system, hydrogen interaction, for example with His164, Ser144, and Cys145, and halogen bond interaction with the thiol group of Cys44 through its chloro group. In-vitro studies show a limited inhibitory capacity on M-pro (3.97% at 50 \(\upmu\)M) of drug **1** therefore this molecule could be considered a promising compound for the synthesis of more potent and effective inhibitors [45]. In 2022, [PERSON] et al. [5] identified carvediol ((1-(9\(H\)-carbazol-4-yloxy)-3-[2-(2-methoxyphenyloxy)ethylamine]propan-2-ol)) **(2, Figure 2)**, a \(\beta\)-adrenergic receptor blocker, as Mpro inhibitor by _in-silico_ and in-vitro assays. In silico studies allowed us to study the conformational changes in the enzyme induced by the different ligands. From the evaluation of the data obtained, it was possible to identify combinations of molecules that gave a synergistic effect on protease Mpro. In fact, the drug combination favipiravit (6-fluoro-3,4-dihydro-3-oxo-2-pyrazinecarboxamide)/ carvediol **(2)** was found to be active against this enzyme. The inhibitory activity tests the evaluation of the synergistic effect and was evaluated by using the \"3 CL Protease (SARS-CoV-2) Assay Kit\" from \"BPS Bioscience.\" The best results have been obtained by mixing 2 \(\upmu\)M compound **2** and 1 \(\upmu\)M favipiravit showing an inhibition percentage of 98 and a contact-dependent growth inhibition (CDI) of 0.89. CF analysis (analysis of contact frequency) and MD simulation (molecular dynamics simulations) were able to identify the amino acid residues that affect the bond between compound **2** and Mpro (for example His41, Met49, and Thr25 showed more than 80% CF; Cys44, Ser46, and Glu166 more than 70%) [5]. This study supports the computational work carried out in 2020 by [PERSON] et al., showing the important role of carvediol in the treatment of COVID-19 [46; 78] and that of [PERSON] et al. [17] reporting carvediol as a potential protease inhibitor similar to 3-chymotrypsin SARS-CoV-2. Carvediol **(2)** was also used in a clinical trial to evaluate the clinical outcomes of hypertensive patients infected with SARS-CoV-2, who commonly use inhibitors of the renin-angiotensin-aldosterone system. The study conducted by [PERSON] et al. [47] confirmed that there are no deleterious effects following the use of angiotensin-converting enzyme inhibitors (ACEis) and angiotensin receptor blockers (ARBs) in hypertensive patients with COVID-19 [48]. Also, according to the report of [PERSON] et al. [9] in 2021, drugs such as carvediol **(2)** may control the development of HF by reducing the infectivity of the 2019 novel coronavirus (SARS-CoV-2) and prevent the production of cytokine storms in severely affected COVID-19 people. Compound **2** downregulates cardiac ACE2 and inhibits SARS-CoV-2-induced acute cardiac injury [49]. [PERSON] et al. demonstrated that **2** can moderate the development of paraquat-induced ALI through suppression of oxidative stress and NF-kB signaling pathway [79].