Computational study on mechanism of G-quartet oligonucleotide T40214 selectively targeting Stat3

Abstract

The mounting evidences have shown that signal transducer and activator of transcription 3 (Stat3) is a critical target for cancer therapy. Recently, we developed a G-quartet oligonucleotide T40214 as a novel and potent Stat3 inhibitor. T40214 specifically inhibited DNA-binding activity of Stat3 and significantly suppressed the growth of many tumor xenografts in nude mice. To determine the mechanism of GQ-ODNs selectively targeting Stat3, we established a 3D model of complex T40214/p-Stat3 dimer based on experimental evidences. The binding site of T40214 within Stat3 dimer was determined by statistical docking analysis. The results indicated that T40214 strongly interacted within the region from residue E638 through E652 of Stat3 dimer. The binding model refined by Hex docking disclosed that T40214 binds to SH2 domain of Stat3 and forms H-bonds with residues Q643, Q644, N646, and N647, which are critical for the binding interaction. The 3D models also suggested that T40214 inhibits Stat3 activity through disrupting the binding interaction between Stat3 dimer and DNA duplex for transcription. Our computational studies provided a platform for future structure-based drug design of novel Stat3 inhibitors.

Signal Transducer and Activator of Transcription 3 (STAT3) Regulates Collagen-Induced Platelet Aggregation Independently of Its Transcription Factor Activity

“…To validate data generated with STA21, we also tested the oligonucleotide G-quartet T40214, a different class of STAT3 inhibitor that specifically blocked phosphorylation-dependent STAT3 dimerization 17;18 . Compared to those treated with a scrambled control oligonucleotide, T40214 significantly reduced the aggregation of human platelets induced by 5 μg/ml, but not 10 μg/ml of collagen (Figure 2A & 2B).…”

“…It is in a linear structure in low extracellular [K + ] (~5 mM), but forms a symmetrical G-quartet structure in high intracellular [K + ] (~140 mM) when it is delivered into cells using polyethyleneamine nanobeads (PEI, MW ~25,000, Aldrich Chemical, WI) as a carrier 17 . It binds the SH2 domain of STAT3 to inhibit the tyrosine phosphorylation and dimerization of STAT3 18;19 . T40214 and a scrambled control oligonucleotide (CGGGGCGGGGCGGGGC) were commercially synthesized (Midland Certified Reagent Co., Midland, TX) and purified by anion exchange high pressure liquid chromatography on Q Sepharose followed by pressure filtration in H 2 O.…”

Transcription Factor STAT3 as a Novel Molecular Target for Cancer Prevention

“…The reduced expression of these gene products inhibits proliferation and increases apoptosis in a variety of tumor cell lines [194,195] and induces tumor regression in xenograft models [196,197]. The G-quartet ODN, which forms four-stranded G-quartet structures [154], uses another mechanism: it disrupts STAT3:STAT3 dimers and inhibits STAT3 binding to DNA [155], thereby inducing tumor cell apoptosis and tumor regression [156,157,193]. Another effective method of blocking STAT3 activity with ODNs is the use of siRNA to degrade STAT3 mRNA.…”

Nucleic Acid Aptamers Based on the G-Quadruplex Structure: Therapeutic and Diagnostic Potential

“…They promoted apoptosis and reduced angiogenesis and cell proliferation. Computer-assisted docking analysis revealed that the oligonucleotide is likely folded into a G-4 structure and interacts with the SH2 domains of Stat3 homodimers thereby destabilizing dimer formation and reducing DNA-binding activity [54]. Moreover, it forms Hbonds with residues Q643, Q644, N646, and N647, which are critical for the binding interaction.…”