Novel Small Molecules Disabling the IL-6/IL-6R/GP130 Heterohexamer Complex PRINCIPAL INVESTIGATOR:

The IL-6/GP130/STAT3 pathway is critical forthe progression of multiple types of cancers. We report here thediscovery of raloxifene and bazedoxifene as novel inhibitors of IL-6/GP130 protein−protein interactions (PPIs) using multipleligand simultaneous docking (MLSD) and drug repositioningapproaches. Multiple drug scaffolds were simultaneously dockedinto hot spots of GP130 D1 domain by MLSD to compete withthe key interacting residues of IL-6, followed by tethering togenerate virtual hit compounds. Similarity searches of virtual hitson drug databases identified raloxifene and bazedoxifene aspotential inhibitors of IL-6/GP130 interaction. In cancer cellassays both compounds bind to GP130 and demonstratedselective inhibition of IL-6 induced STAT3 phosphorylation andwere significantly more potent than the previously reportednatural product inhibitor MDL-A. The identified drugs represent a new class of lead compounds with piperidine,benzothiophene, and indole scaffolds to inhibit IL-6 induced homodimerization of GP130. Besides potential direct usage forclinic trials, the two compounds can also serve as lead compounds for optimization to speed the development of drugs selectivelytargeting the IL-6/GP130/STAT3 cancer signaling pathway. ■ INTRODUCTIONInterleukin-6 (IL-6) is a cytokine involved in variousinflammatory and immune responses, cellular apoptosis, andproliferation, etc. IL-6 binds to IL-6Rα to form a binarycomplex and then recruits GP130 to form the IL-6/IL-6Rα/GP130 heterotrimer. Furthermore, homodimerization of theIL-6/IL-6Rα/GP130 heteotrimers occurs by interactionsbetween IL-6 of one trimer and the D1 domain of GP130 ofthe other trimer, forming a hexamer (Figure 1). Thereciprocal homodimerization of the IL-6/IL-6Rα/GP130trimers triggers a signaling cascade of phosphorylation ofJanus kinases (JAKs) and a downstream effector STAT3,followed by reciprocal dimerization of the Tyr705-phosphory-lated STAT3, resulting in STAT3 nucleus translocation, DNAbinding, and multiple oncogene transcriptions.Previous studies indicated that IL-6 and the major down-stream effector STAT3 are protumorigenic agents in manycancers, supporting both as attractive therapeutic targets.Madindoline A (MDL-A), a natural product compound, wasreported as a highly selective, non-peptide antagonist toGP130. It was confirmed that MDL-A binds to the extracellular domain of GP130 and inhibits IL-6 dependent STAT3 tyrosine phosphorylation in HepS2 (hepatocellularcarcinoma) cells. However, this natural product cannot be developed into an effective drug because (a) it is no longer available from natural resources, (b) the total synthesis involves many steps, and the low yield makes it not economically practical, and (c) its binding to GP130 is relatively weak (Kd of288 μM). Although a few MDL-A analogues were identified to inhibit the homodimerization of GP130 via virtual screeningand structure based drug design, synthesis of these analogues requires many steps, resulting in yields too low to be practical for drug development. Therefore, it is highly desirable to design and identify novel, small molecule drugs to disable this Received: July 27, 2013Published: January 23, 2014Article