Optimation of the lead MD77

The investigation which led to the identification of our lead MD771 began from a screening (dual-luciferase assay system) of chemical libraries, performed in collaboration with our colleagues of the Korean Research Institute of Bioscience and Biotechnology (KRIBB). From this preliminary screening, several STAT3 inhibitors were identified. Based on the further information gained through conformational and docking studies, a number of derivatives were synthesized, characterized and evaluated by means of different biological assays. The obtained results led to the discovery of a molecule (MD77) as a promising lead compound. MD77 exerted positive results in the dual-luciferase assay, showing 20% inhibition at 5 μM. It was also able to significantly interact with STAT3-SH2 domain, with a dose-dependent profile and an IC50 of 17.7 μM (AlphaScreen-based assay). Moreover, it displayed a significant growth inhibitory activity evaluated on a panel of tumor cell lines with a GI50 around 2 μM for most of them. Modeling, docking and crystallographic studies were also performed and they gave a key support in understanding the binding mode of MD77 to the STAT3-SH2 domain. In light of these results, MD77 became our starting point for the development of new direct STAT3 inhibitors. Initially, the optimized derivatives were designed following the classical methodologies of medicinal chemistry, in which the molecule undergoes a gradual modification on the basis of SAR studies and with the support of molecular modeling studies. In particular, the substitution of the amidic functionality with a bioisosteric thioamidic group and the nature of the substituent at position 5 were considered. In detail, alkyl groups or halogens were introduced at different positions of the aromatic ring. In addition, since docking studies on MD77 suggested that in the binding mode of its favoured conformation to the SH2 domain, which is comparable to that of phosphorylated Tyr-705, the trifluoromethyl group could play an important role by establishing three hydrogen bond interactions with the guanidine moiety of Arg-595 residue, we synthesized the analogue lacking the substituent to verify this hypothesis. 1. Masciocchi D., Villa S., Meneghetti F., Pedretti A., Barlocco D., Legnani L.,Toma L., Kwon BM, Nakano S., Asai A., Gelain A. Biological and computational evaluation of an oxadiazole derivative (MD77) as a new lead for direct STAT3 inhibitors. MedChemComm (2012), 3, 592-599