Opportunities for protein kinase drug discovery – 2025 update on the chemically underexplored human kinome

As a part of the Illuminating the Druggable Genome initiative, the U.S. National Institutes of Health (NIH), identified 162 understudied human protein and lipid kinases forming the “dark” kinome. In protein kinase (PK) drug discovery, the dark kinome has become a focal point in the search for new PK targets with interesting disease biology and lack of high-quality PK inhibitors (PKIs) for therapeutic intervention. Major criteria for the identification of dark kinases applied by the NIH included the lack of functional information and reagents for functional studies. We have previously introduced an alternative chemistry-centric assessment of understudied PKs that was based on a detailed analysis of the PKI coverage of the human kinome. This concept made it possible to differentiate between PKs based of their degree of chemical exploration. Given the continuing growth of PKI data in the public domain, we have repeated the analysis of chemically explored, underexplored, and unexplored PKs and updated the previous PK classification. As a part of our study, all PK and PKI data curated for our analysis are made publicly available together with the up-to-date chemical exploration-based PK classification and its comparison to the dark kinome. The curated data and kinome classification should be a useful resource for PK target prioritization and medicinal chemistry. Shown is a phylogenetic tree rendering of the human kinome. Chemically under- and unexplored protein kinases are represented as red and blue dots, respectively.