# Carbazole Derivatives as STAT Inhibitors: An Overview
## 3 STATs Inhibitors
### Carbazoles as STAT Inhibitors
With this in mind, an in-depth investigation of acetyl-STAT3 and DNMT1 status in human cancers could offer a potential therapeutic opportunity with the aim of targeting the STAT3-DNMT1 interaction [113]. [PERSON] et al. in 2019 [114] evaluated the anticancer effect of **16**, too. They assessed that PI3K/AKT/mTOR, JAK/STAT or SRC were the main activated pathways in cell-of-origin sarcoma models and/or sarcoma primary cell lines. Compound **16** blocked the phosphorylation of these targets and impeded proliferation triggering the DNA damage, cell cycle arrest, and apoptosis. Moreover, **16** in part decreased tumor growth _in vivo_. Furthermore, it decreased the expression and the effect of ABC efflux pumps implicated in drug resistance. Data also suggested that combining compound **16** with doxorubicin resulted in a synergistic cytotoxic effect in vitro and an enhanced antitumor effect in the animal model. They found that **16** is much more successful than midostaurin in preventing the phosphorylation of ERK1/2 at Thr202 and Tyr204, AKT at Ser473 and Thr308, p56 at Ser235 and Ser236 and 4 EBP at Ser65, which are the kinases/kinase substrates most enabled  
Figure 11: Structure of (5R,7S,9S)-7,8-dihydroxy-9-methyl-6,7,8,9-tetrahydro-5H,14H-17-oxa-4b,9a,15-triaza-5,9-methanandobenz[b,h]cyclonona[jkl]cyclopenta[e]-as-indacene-14,16(15H)-dione (EC-70124, **16**). among a panel of relevant signaling molecules in a cell model of MRCLS. Furthermore, **16** prevented the activation of SRC, STAT1, and STAT3, activated in several primary sarcoma cell lines. The multikinase inhibitory effect of **16** in sarcomas is linked to a potent antiproliferative activity if compared with midostaurin. This is due to the induction of DNA damage followed by a more stringent S-phase arrest and apoptosis. In addition, it is known that midostaurin and other indolocarbazoles inhibit Aurora kinase abrogating the mitotic spindle checkpoint and the accumulation of cells with 4 N and 8 N DNA content [114]. In 2015 [PERSON] et al. [115] synthesized a series of 1,4-dimethyl-carbazole derivatives (Figure 12) and tested them for their potential activity on STAT3. The design of molecules has been assisted by in silico studies with the purpose to identify new ligands of SH2 domain of STAT3 responsible for the protein dimerization, where a monomer identifies the Pro-Tyr/pTyr-Leu-Lys-Thr-Lys sequence of its partner. Indeed, the in silico analysis was performed by selecting the protein region accommodating the Pro-Tyr/pTyr-Leu-Lys-Thr-Lys sequence and especially the interactions involving the Tyr/05/pTyr705, essential for the possible ligand binding. Therefore, the possible effects on the cellular viability of human melanoma (A375) and human epithelial cervix adenocarcinoma (HeLa) cell lines, which constitutively express STAT3, have been evaluated. Their findings evidenced that 1,4-dimethyl-carbazole (**17**) (IC\({}_{50}\) of 80.0 uM) had similar activity to doxorubicin (IC\({}_{50}\) of 87.0 uM), used as a reference molecule, toward A375 cells. Compounds **18**, **20**, **24**, and **26** achieved a similar trend of results on both cell lines in comparison with doxorubicin whereas compounds **19** and **21** exhibited IC\({}_{50}\) values on A375 of 50 and 60 uM, respectively. Moreover, the most active compounds **19-21** displayed a considerable inhibition rate at 72h of STAT-3 expression with respect to the control cells, with a percentage of inhibition amounting to 94.33, 90.66, and 91.0 %, respectively. In silico studies revealed that the position 6 of carbazole ring faces the cavity accommodating the Tyr/05/pTyr705. Specifically, this research group verified that the Tyr/05/pTyr705 is in a small hollow, to interact with the side chains of Lys591, Arg609, Ser611, Glu612 and Ser613. For this reason, they designed compounds **18-22** inserting at C-6 a hydrogen bond acceptor to replicate this interaction. Furthermore, they added hydroxyl, methoxy, ethyl ester groups, and a chlorine and a sulfonamide function.