# Carbazole Derivatives as STAT Inhibitors: An Overview
## 3 STATs Inhibitors
### Carbazoles as STAT Inhibitors
ACB downregulated the nuclear pool of phospho-STAT3 pointing out that **30** suppresses the phosphorylation of STAT3, thereby translocating into the nucleus and reducing its DNA binding ability. LSD1 was exploited as nuclear marker and loading control for nuclear protein. The levels of LSD1, cytoplasmic STAT3 and \(\beta\)-actin did not vary. These data were also confirmed by in silico studies that determined the acetyl group on the core carbazole as the most auspicious substituent. In particular, in different matched molecular series, compounds bearing the acetyl group showed the best cellular activities. An ethyl substituent is related to a modest solubility of the corresponding compounds, particularly in relation to chlorine substitutions. On the contrary, they explored \(N\)-substituents and found the 3-(2-cyano-phenyl)-benzyl substitution as decoration with the highest effects in two out of three matched molecular series. Moreover, they extracted the SH2 domain from the crystal structure of the STAT3 homo-dimer and chose the pTyr as the center for in silico docking experiments. The 3-(2-cyano-phenyl)-benzyl substituted compounds such as **30**, **31**, and **32** demonstrated distinct features in molecular docking apart from conserved shape fit and hydrophobic interactions. The substituents on the carbazole moiety were buried in the pTyr binding site and thereby form hydrogen bonds via the acetyl and hydroxyethyl group. This provides a clarification of the better activity of the acetyl and ethyl decoration over the ethyl one, which misses the acceptor functionality resembling the pTyr in binding to the side chain of Arg609. [PERSON] et al. in 2011 [118] explored the possible activity of Lesaturtinib against HL based on the knowledge that JAK/STAT pathway constitutive activation is involved in [PERSON]'s lymphoma (HL) pathogenesis and the ability of Lesaturtinib (formerly known as CEP-701, 33 Figure 15) to inhibit JAK2 and FLT3 [119] in myeloproliferative disorders. Genomic gains of JAK2 [120], due to 9p24 gains [121], and SOCS1, a negative regulator of JAK/STAT signaling, are often somatically mutated and inactivated in HL [122]. Besides, constitutive activation of STAT3 has been documented in HL cell lines [123]. To verify, they treated five HL cell lines from refractory patients, L-428, L-1236, L-540, HDML-2, and HD-MY-Z with Lesaturtinib. They noticed a dose-dependent cell growth suppression (23%-66% at 300 nM) and an apoptotic increase (10%-64% at 300 nM) after treatment for 48 h. Furthermore, Lesaturtinib prevented JAK2, STAT5, and STAT3 phosphorylation and decreased the mRNA expression of its downstream antiapoptotic  
Figure 14: Carbazol-carbonitrile derivatives (**30–32**). target Bcl-xL. Furthermore, they determined after 1 h, phospho-JAK2 levels were reduced in all the HL cell lines by 46-94% at 300 nM, whereas no substantial changes were detected in JAK2 total protein expression. Lestaurtinib markedly hampered the phosphorylation of STAT5 and STAT3. However, no substantial changes in STAT5 and STAT3 total protein were assessed. Phospho-STAT5 and phosphoSTAT3 levels declined by 88-100% and by 97-100%, respectively, after 1 h of 300 nM of Lestaurtinib treatment. Bcl-xL, a pro-survival protein triggered by phosphorylated STAT5 DNA binding, is upregulated in HL samples, and is implicated in apoptotic resistance in HRS cells. Reduced phosphorylation of STAT5 resulted in lowered mRNA expression of its downstream antiapoptotic effector Bcl-xL. Cells were treated for 1 h with Lestaurtinib at 300 nM discovering that Bcl-xL mRNA expression levels diminished by 52% in L-428, 28% in L-1236, 37% in L540, 55% in HDLM-2, and 71% in HD-MY-Z [124]. Subsequently, [PERSON] et al. [125] carried out a phase 2 study of CEP-701 in which 22 JAK\({}^{2}\)V617F-positive patients with myelofibrosis, for which few therapeutic options are available today, were treated with 80 mg, orally twice daily, of this drug. The total response rate for the patients was of 27%, with a median time to response of three months.