TGF-β receptor-specific NanoBRET Target Engagement in living cells for high-throughput kinase inhibitor screens

Targeting transforming growth factor-β (TGF-β) receptors is a promising pharmacological approach to normalize aberrant signaling in genetic and non-genetic TGF-β associated diseases including fibrosis, cancer, cardiovascular and musculoskeletal disorders. To identify novel TGF-β receptor kinase inhibitors, methods like in vitro kinase assays, western blot or transcriptional reporter assays are often used for screening purposes. While these methods may have certain advantages, the lack of integration of key features such as receptor specificity, high-throughput capability, and cellular context resemblance remains a major disadvantage. This deficiency could ultimately hinder the translation of study outcomes into later (clinical) stages of drug development. In this study, we introduce an adjusted and optimized live cell NanoBRET Target Engagement (TE)-based method to identify TGF-β receptor specific kinase inhibitors. This comprehensive toolkit contains various TGF-β type I and type II receptors, with corresponding nanoBRET tracers, and disease-related cell lines, including novel non-commercially available materials. The nanoBRET capacity and kinase inhibitory window can be significantly enhanced for functional measurements when stable expression cell lines and substantially low tracer concentrations are used. In addition, this system can be tailored to study TGF-β associated genetic disorders and possibly be used to screen for disease-specific therapeutics. Therefore, the use of this optimized, live cell, antibody-independent nanoBRET Target Engagement assay is highly encouraged for future high-throughput compound screens targeting TGF-β/BMP receptors.