Mass spectrometry-based decoding enables rapid identification of therapeutic candidates from half-million compound libraries

Drug discovery has long relied on affinity selection technologies to rapidly screen vast chemical libraries for molecules that bind therapeutic targets. While DNA-encoded libraries have transformed this landscape by enabling the screening of billions of compounds through unique genetic barcodes, they come with significant limitations. The DNA tags themselves create synthesis complexity, restrict chemical reaction compatibility, and can interfere with binding assays, particularly for targets that naturally interact with nucleic acids like transcription factors and DNA-processing enzymes.

Recent advances in mass spectrometry instrumentation and computational annotation algorithms have now made barcode-free screening a reality. Researchers have developed self-encoded libraries that identify compounds directly through their tandem mass spectrometry fragmentation patterns rather than external tags. This approach combines solid-phase combinatorial synthesis with automated structure annotation software called COMET, which predicts fragmentation patterns and filters mass spectrometry data to accurately identify library members. The platform has successfully screened libraries containing over 500,000 small molecules in single experiments, matching the scale of functional DNA-encoded library selections while avoiding the constraints of genetic barcoding.

The self-encoded library workflow enables synthesis protocols that would degrade DNA tags, including palladium-catalyzed cross-couplings, heterocyclizations, and nucleophilic aromatic substitutions. Libraries can be synthesized in under a week using standard organic chemistry techniques, democratizing access to large-scale screening beyond well-funded pharmaceutical companies. Validation studies against carbonic anhydrase IX identified multiple nanomolar binders with enrichment factors comparable to phage display selections. More significantly, the platform succeeded where DNA-encoded approaches cannot, discovering potent inhibitors of flap endonuclease 1, a DNA-binding enzyme whose active site would be compromised by the presence of oligonucleotide tags. The absence of bulky barcodes allows library compounds to explore broader conformational diversity during selection and eliminates false positives caused by DNA-target interactions. With detection limits suggesting scalability to five million compounds and the ability to screen diverse chemical scaffolds simultaneously, this barcode-free technologyrepresents a transformative step for early-stage therapeutic development.