Abstract
Signal transducer and activator of transcription 3 (STAT3) is a validated anticancer target due to the relationship between its constitutive activation and malignant tumors. Through a virtual screening approach on the STAT3-SH2 domain, 5,6-dimethyl-1H,3H-2,1,3-benzothiadiazole-2,2-dioxide (1) was identified as a potential STAT3 inhibitor. Some benzothiadiazole derivatives were synthesized by employing a versatile methodology, and they were tested by an AlphaScreen-based assay. Among them, benzosulfamide 1 showed a significant activity with an IC50 = 15.8 ± 0.6 µM as a direct STAT3 inhibitor. Notably, we discovered that compound 1 was also able to interact with cysteine residues located around the SH2 domain. By applying mass spectrometry, liquid chromatography, NMR, and UV spectroscopy, an in-depth investigation was carried out, shedding light on its intriguing and unexpected mechanism of interaction.
Highlights
Since the discovery of the relationship between the constitutive activation of signal transducer and activator of transcription 3 (STAT3) and malignant tumors, the validation of STAT3 as a target has been supported by a large number of studies
We found that lipophilicity does not play an an important role in modulating STAT3 inhibitory activity
We investigated the importance of the thiadiazole ring (5 and 6) through the exploration of the function of the SO2 group and of the nitrogen atoms: The results of the AlphaScreen-based assay indicated that these moieties play a key role in the interaction with the STAT3-Src homology homology 22 (SH2) domain
Summary
Since the discovery of the relationship between the constitutive activation of signal transducer and activator of transcription 3 (STAT3) and malignant tumors, the validation of STAT3 as a target has been supported by a large number of studies. Various compounds with STAT3 inhibitory activity have been reported in recent years, including potent inhibitors such as Stattic, S3I-201, and erasin [1,2,3,4]. These molecules are mostly at the experimental stage, and only few are in clinical trials [5]. The large surface area of STAT3 and the chemistry of these interactions [6], which are very different from those of better-known targets such as enzymes and G-protein-coupled receptors, could represent significant hurdles, a number of successful examples have demonstrated that it is Molecules 2020, 25, 3509; doi:10.3390/molecules25153509 www.mdpi.com/journal/molecules
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