Degradation of certain proteins through the ubiquitin-proteasome pathway is a common strategy taken by the key modulators responsible for stress responses. Kelch-like ECH-associated protein-1(Keap1), a substrate adaptor component of the Cullin3 (Cul3)-based ubiquitin E3 ligase complex, mediates the ubiquitination of two key modulators, NF-E2-related factor 2 (Nrf2) and IκB kinase β (IKKβ), which are involved in the redox control of gene transcription. However, compared to the Keap1-Nrf2 protein-protein interaction (PPI), the intermolecular recognition mechanism of Keap1 and IKKβ has been poorly investigated. In order to explore the binding pattern between Keap1 and IKKβ, the PPI model of Keap1 and IKKβ was investigated. The structure of human IKKβ was constructed by means of the homology modeling method and using reported crystal structure of Xenopus laevis IKKβ as the template. A protein-protein docking method was applied to develop the Keap1-IKKβ complex model. After the refinement and visual analysis of docked proteins, the chosen pose was further optimized through molecular dynamics simulations. The resulting structure was utilized to conduct the virtual alanine mutation for the exploration of hot-spots significant for the intermolecular interaction. Overall, our results provided structural insights into the PPI model of Keap1-IKKβ and suggest that the substrate specificity of Keap1 depend on the interaction with the key tyrosines, namely Tyr525, Tyr574 and Tyr334. The study presented in the current project may be useful to design molecules that selectively modulate Keap1. The selective recognition mechanism of Keap1 with IKKβ or Nrf2 will be helpful to further know the crosstalk between NF-κB and Nrf2 signaling.

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Protein kinase CK2 (CK2), a ubiquitous serine/threonine protein kinase for hundreds of endogenous substrates, serves as an attractive anticancer target. One of its most potent inhibitors, CX-4945, has entered a phase I clinical trial. Herein we present an integrated workflow combining shape-based virtual screening for the identification of novel CK2 inhibitors. A shape-based model derived from CX-4945 was built, and the subsequent virtual screening led to the identification of several novel scaffolds with high shape similarity to that of CX-4945. Among them two tricyclic scaffolds named [1,2,4]triazolo[4,3-c]quinazolin and [1,2,4]triazolo[4,3-a]quinoxalin attracted us the most. Combining strictly chemical similarity analysis, a second-round shape-based screening was performed based on the two tricyclic scaffolds, leading to 28 derivatives. These compounds not only targeted CK2 with potent and dose-dependent activities but also showed acceptable antiproliferative effects against a series of cancer cell lines. Our workflow supplies a high efficient strategy in the identification of novel CK2 inhibitors. Compounds reported here can serve as ideal leads for further modifications.

NF-κB is a significant transcription factor that regulates the expression of various pro-survival genes. IKK is a crucial protein kinase that activates NF-κB translocating from cytoplasm to nucleus for DNA binding. It is composed of three subunits, IKKα, IKKβ, IKKγ (NEMO), where IKKα and IKKβ are catalytic subunits, and IKKγ is the regulatory subunit. Many diseases, such as Hodgkin's disease, Hepatitis-associated hepatocellular carcinoma, colorectal cancer, prostate cancer, rheumatoid arthritis and inflammatory bowel disease, are related to IKK and NF-κB. So far, various IKK inhibitors targeting the ATP binding site have been identified through high throughput screening, rational design or in silico methods, however, only three of them (CHS-828, EB-1627 and IMD-1041) have been under clinical studies, indicating the strategy for the design of IKK inhibitors need to be reinspected. Besides ATP-competitive inhibitors, several other inhibitors have also been disclosed recently, which provide novel concepts to the discovery of IKK inhibitors. In this review, we focus on two parts: 1) the chemotypes and binding patterns of the traditional ATP-competitive IKK inhibitors; 2) novel strategies for the identification of non-ATP-competitive IKK inhibitors as NF-κB modulators. Through these discussions we hope to present inspirations for the development of new IKK inhibitors.