Disruption of Transcriptionally Active Stat3 Dimers with Non‐phosphorylated, Salicylic Acid‐Based Small Molecules: Potent in vitro and Tumor Cell Activities

Abstract

Signal transducer and activator of transcription 3 (Stat3) protein is a cytosolic transcription factor that relays signals from receptors in the plasma membrane directly to the nucleus, and is routinely hyperactivated in many human cancers and diseases. [1] Regarded as an oncogene, Stat3 is well-recognized as a master regulator of cellular events that lead to the cancer phenotype, making this protein viable target for molecular therapeutic design. [2] Stat3 inhibitors have included peptides, [3][4] peptidomimetics, [5][6][7][8][9] small molecules [10][11][12][13][14] and metal complexes.[15] Despite significant advances in Stat3 inhibition, [1] truly potent (in vivo), isoform-selective, small molecule Stat3 agents have not been readily forthcoming; this is likely due in part to the challenge of disrupting protein-protein interactions. [16] The canonical view of Stat3 signaling describes inactive Stat3 monomers located predominantly within the cytoplasm. The Stat3 activation pathway begins with a cytokine or growth factor ligand interaction with the extracellular domain of a transmembrane receptor. Subsequently, receptor-associated tyrosine kinases such as the Janus kinases (Jaks) are induced to phosphorylate tyrosine residues on the specific receptor's cytoplasmic domain. These phosphorylated residues then serve to recruit latent Stat monomers through interaction with their SH2 domains. Tyrosine-kinase-mediated phosphorylation of Tyr705 on Stat3 monomers induces Stat3-receptor dissociation and Stat3-Stat3 homodimerization through reciprocal phosphotyrosine (pTyr)-SH2 domain interactions. The resulting transcriptionally active Stat3 dimers then translocate to the nucleus, where they bind to specific DNAresponse elements in the promoters of target genes and induce antiapoptotic gene expression programs (e.g., Bcl-x L ) and the overexpression of cell cycle regulators (for example, cyclin D 1 ).[17] Current programs of research, including our own, have focused on inhibiting the Correspondence to: Patrick T. Gunning, patrick.gunning@utoronto.ca. NIH Public Access Author ManuscriptChembiochem. Author manuscript; available in PMC 2010 August 10. Figure 1A; IC 50 = 86 μM) through in silico structure-based virtual screening of National Cancer Institute chemical libraries.[12] We sought to optimize lead agent S3I-201 through rational, synthetic modifications with the global objective of obtaining isoform-selective, Stat3 inhibitors displaying potency at low to submicromolar concentrations. S3I-201 is based on a glycolic acid scaffold whose carboxylic acid functionality has been condensed with 4-aminosalicylic acid to furnish the amide bond, and whose hydroxyl has been tosylated ( Figure 1A). The Stat3 SH2 domain is broadly composed of three subpockets, but GOLD [18] docking studies showed that S3I-201 can access only two of these subpockets simultaneously ( Figure 1B), and this identified a potential means of improving inhibitor potency. The salicylic (ortho-hydroxybenzoic) acid component of S3I-201 is a known pTyr ...

Changes in Signal Transducer and Activator of Transcription 3 (STAT3) Dynamics Induced by Complexation with Pharmacological Inhibitors of Src Homology 2 (SH2) Domain Dimerization

“…6, A and B). The side chain of Arg-609, mapping near the peptide LRFSE (608 -612), was predicted to hydrogen bond with the salicylic acid moiety common to both inhibitors, greatly stabilizing the binding energy of the molecules (8,22). This is consistent with large decreases in backbone deuteration observed in the LRFSE (608 -612) peptide given the tight predicted occupancy of this subpocket by the salicylic acid moiety for both inhibitors.…”

Potent Targeting of the STAT3 Protein in Brain Cancer Stem Cells: A Promising Route for Treating Glioblastoma

“…To circumvent these problems, our group has developed novel small molecule STAT3 inhibitors not containing a phosphate ester. 16,17 Using structure-based design, targeting the pTyr-SH2 domain interactions, salicylic acid-based inhibitors have been identified that block STAT3 dimerization and DNA-binding, namely, BP-1-102 (1, Figure 1). BP-1-102 potently suppresses cell proliferation, migration, invasion, and motility.…”

A potent and selective inhibitor for the UBLCP1 proteasome phosphatase

“…Interestingly, salicylic acid derivatives have also subsequently been found as pTyr mimetics for SHP2 domain proteins. 35–37 Importantly, we demonstrated that PTP inhibitor potency and selectivity can be achieved by tethering molecular fragments to an appropriate bicyclic salicylic acid core to engage both the active site and an adjacent binding pocket. 28,30–33 Given the success with the PTPs, we initially set out to discover UBLCP1 inhibitors by screening the benzofuran and indole-based salicylic acid libraries already prepared in the laboratory.…”