Unexpected Noncovalent Off-Target Activity of Clinical BTK Inhibitors Leads to Discovery of a Dual NUDT5/14 Antagonist.

Cofactor mimicry represents an attractive strategy for the development of enzyme inhibitors but can lead to off-target effects due to the evolutionary conservation of binding sites across the proteome. Here, we uncover the ADP-ribose (ADPr) hydrolase NUDT5 as an unexpected, noncovalent, off-target of clinical BTK inhibitors. Using a combination of biochemical, biophysical, and intact cell NanoBRET assays as well as X-ray crystallography, we confirm catalytic inhibition and cellular target engagement of NUDT5 and reveal an unusual binding mode that is independent of the reactive acrylamide warhead.

Open resources for chemical probes and their implications for future drug discovery.

Introduction: The rational development of new therapeutics requires a thorough understanding of how aberrant signalling affects cellular homeostasis and causes human disease. Chemical probes are tool compounds with well-defined mechanism-of-action enabling modulation of, for example, domain-specific protein properties in a temporal manner, thereby complementing other target validation methods such as genetic gain- and loss-of-function approaches.

Areas Covered: In this review, the authors summarize recent advances in chemical probe development for emerging target classes such as solute carriers and ubiquitin-related targets and highlight open resources to inform and facilitate chemical probe discovery as well as tool compound selection for target validation and phenotypic screening.