Biochemical Assay: Through the Molecular Library Probe Production Center Network (MLPCN), at least 300,000 compounds were screened using a TR-FRET method, an ALPHASCREEN method or both, and tested for their ability to inhibit SUMOylation of a target protein via SUMO E1 or SUMO E2. The assays were based on SUMOylation of the target protein RanGAP1, which is a protein that is efficiently SUMOylated with only the SUMO E1 and E2 enzymes, and does not use E3 ligases. A fluorescence resonance energy transfer (FRET) assay was the primary assay followed by a chemoluminescence-based secondary assay using ALPHA screen to eliminate false positive hits. Then, the hits were screened by a poly-ubiquitination assay using ubiquitin, ubiquitin E1, Ubc5 and Apc11 to eliminate inhibitors not specific to SUMOylation. The screening identified a potent family of SUMOylation inhibitors based on a tricyclic scaffold.