# An Update of Carbazole Treatment Strategies for COVID-19 Infection
## 4 Carbazoles Treatment
### Viral-Entry Inhibitors Targeting Human ACE2  
[PERSON] et al. in 2020 [54] have identified the carbazole edotecarin (**8**, Figure 4), (6-(1,3-dihydroxypropan-2-yl)amino)-2,10-dihydroxy-12-((2\(R\),3\(R\),4\(S\),5\(S\),6\(R\))-3,4,5-trihydroxy- 6-(hydroxymethyl))tetrahydro-2\(H\)-pyran-2-yl)-12,13-dihydro-5\(H\)-indol[2,3-\(a\)]pyrrolo[3,4-\(c\)]carbazole-5,7(6\(H\))-dione) as viral-entry inhibitors targeting human ACE2 by molecular docking. Figure 3: Structures of: koenigicine **(3**), mukonicine **(4**), O-methylmurrayamine A (5), koenine **(6)** and girinimbine (7). Compound **8**, by means of electrostatic interactions, favors the closed (substrate/inhibitor-bound) conformation of angiotensin-converting enzyme 2 modifying the positions of the receptor's amino acids interested in recognition by SARS-CoV-2. Specifically, the diol group of topoisomerase I inhibitor (**8**) is crucial for the interaction; the catalytic residues of ACE2 mainly interested in interacting with **8** are Glu375, Tyr515, and Asn149. Furthermore, **8** with conjugative \(p\)-planes performs pep interactions (sandwich or T-shaped) with the amino acids Phe274, His345, and Tyr510 [50]. As already discussed, modulators of expression levels of proteins such as ACE2 may control the SARS-CoV-2 infection [55]. In 2022, [PERSON] et al. [56] studied the synergistic effect of an analog of edotecarin (**9**, Figure 5) and bafeinib. In particular, with computational methods, they found that 7-hydroxsurosporine (9), ((55,6,7,7,9,16))-16-hydroxy-6-methoxy-5-methyl-7-(methylamino)-6,7,8,9,15,16-hexahdro-17-oxa-4b,9a,15-triaza-5.9-methanodibenzo[b,h] cyclonona[\(jk\)]cyclopenta[e]-as-indacen-14(5\(H\))one), and bafeinib (4-[[(3S)-3-(dimethyl amino)pyrrolidine-1-yl]methyl]-N-[4-methyl-3-[(4-pyrimidin-5-ylpyridimid-2-yl)amino]phenyl]-3-(trifluoromethyl)benzamide), inhibit viral infection when combined together. In vitro studies confirmed that these compounds, used in combination, hinder a post-entry mechanism of the virus and efficacy against the Delta variant. HEK-293 T cells stably expressing human ACE2 and TMPRSS2 (HEK-293 TAT), infected with the SARS-CoV-2 strain isolated from Wuhan, were used for the experiments. The drugs were tested at concentrations of 0.09, 0.9, and 9 uM. Antineoplastic agent **9** and bafeinib (second-generation tyrosine kinase inhibitor) showed significant inhibition at 9 uM. The combination of bafe-tinib and 7-hydroxsurosporine (**9**) on Caco2-ACE2 cells (Caco2 is an immortalized cell linehuman colorectal adenocarcinoma cells) has also been studied using 1 or 3 uM concentrations of drug **9** in combination with 3 uM bafeinib. At 3 uM, the treatment decreased infection by >70%. The synergistic effect was also observed for the Delta variant in a concentration-dependent manner [56; 85; 86]. Another staurosporine analog (**10**, Figure 6)  
Figure 4: Structure of edotecarin (**8**). Figure 5: Structure of 7-hydroxsurosporine (**9**). (sodium 3-(4-(((()-5-5(55,75,8R,95)-8-methoxy-9-methyl-16-oxo-6,7,8,9,15,16-hexahhydro-5H,14H-4b,9a,15-triaza-5,9-methanodibenzo[b,h]cyclonona[jk]cyclopenta[e]-as-indacen-7-yl)-4-oxohexanamido)methyl)-1H-1,2,3-triazol-1-yl)propane-1-sulfonate), called CIMSSNa, was studied in 2022 by [PERSON] et al. as SARS-CoV-2 inhibitor. Experiments conducted on three cell lines (Vero, Huh7 and Calu-3 cells) confirmed that **10** inhibits SARS-CoV-2 and that SARS-CoV-2 enters the cells by direct fusion (at least partly) [57]. Instead, [PERSON] et al. in 2021 [58] proved that treatment with AHR agonists (aryl hydrocarbon receptor agonists), as 6-formylindolo(3,2-_b_)carbazole (**11**, Figure 7), decreases expression of ACE2 via AHR activation, resulting in the suppression of SARS-CoV-2 disease in mammalian cells. The studies were conducted on HepG2 cells. RNA-seq analysis demonstrated that **11** increased CYP1A1 gene expression in a dose-dependent manner and inhibited the expression of the ACE2 gene.