A major challenge associated with biochemical and cellular analysis of pseudokinases is a lack of target-validated small-molecule compounds with which to probe function. Tribbles 2 (TRIB2) is a cancer-associated pseudokinase with a diverse interactome, including the canonical AKT signaling module. There is substantial evidence that human TRIB2 promotes survival and drug resistance in solid tumors and blood cancers and therefore is of interest as a therapeutic target. The unusual TRIB2 pseudokinase domain contains a unique cysteine-rich C-helix and interacts with a conserved peptide motif in its own carboxyl-terminal tail, which also supports its interaction with E3 ubiquitin ligases. We found that TRIB2 is a target of previously described small-molecule protein kinase inhibitors, which were originally designed to inhibit the canonical kinase domains of epidermal growth factor receptor tyrosine kinase family members. Using a thermal shift assay, we discovered TRIB2-binding compounds within the Published Kinase Inhibitor Set (PKIS) and used a drug repurposing approach to classify compounds that either stabilized or destabilized TRIB2 in vitro. TRIB2 destabilizing agents, including the covalent drug afatinib, led to rapid TRIB2 degradation in human AML cancer cells, eliciting tractable effects on signaling and survival. Our data reveal new drug leads for the development of TRIB2-degrading compounds, which will also be invaluable for unraveling the cellular mechanisms of TRIB2-based signaling. Our study highlights that small molecule–induced protein down-regulation through drug “off-targets” might be relevant for other inhibitors that serendipitously target pseudokinases.

The pseudokinase complement of the human kinase superfamily consists of approximately 60 signaling proteins, which lacks one or more of the amino acids typically required to correctly align ATP and metal ions, and phosphorylate protein substrates. Recent studies in the pseudokinase field have begun to expose the biological relevance of pseudokinases, which are now thought to perform a diverse range of physiological roles and are connected to a multitude of human diseases, including cancer. In this review, we discuss how and why members of the 'pseudokinome' represent important new targets for drug discovery, and describe how knowledge of protein structure and function provides informative clues to help guide the rational chemical design or repurposing of inhibitors to target pseudokinases.

Nanoparticles made of metal-organic frameworks (nanoMOFs) are becoming of increasing interest as drug carriers. However, preventing nanoMOFs recognition and clearance by the innate immune system, a prerequisite for biomedical applications, presents an important challenge. In this study we provide a proof of concept that the outer surface of biocompatible iron-based nanoMOFs can be functionalized in a rapid, organic solvent-free and non-covalent manner using a novel family of comb-like copolymers made of dextran (DEX) grafted with both poly(ethylene glycol) (PEG) and alendronate (ALN) moieties. We describe the synthesis and full characterization of DEX-PEG-ALN copolymers by click chemistry, with control of both the amount of grafted PEG and ALN moieties. The copolymers, freely soluble in aqueous media, were used to directly coat the nanoMOFs in water by simple incubation at room temperature. The coating procedure did not affect the nanoMOFs' morphology nor their crystalline structure. As strong iron complexing groups, the ALN moieties ensured multiple cooperative anchoring of the copolymers to the nanoMOFs surface, resulting in stable coatings that substantially decreased their internalization by macrophages in vitro, providing new perspectives for biomedical applications.