Medium-Throughput Detection of Hsp90/Cdc37 Protein–Protein Interaction Inhibitors Using a Split Renilla Luciferase-Based Assay

The protein-folding chaperone Hsp90 enables the maturation and stability of various oncogenic signaling proteins and isthus pursued as a cancer drug target. Folding in particular of protein kinases is assisted by the co-chaperone Cdc37. Severalinhibitors against the Hsp90 ATP-binding site have been developed. However, they displayed significant toxicity in clinicaltrials. By contrast, the natural product conglobatin A has an exceptionally low toxicity in mice. It targets the protein–proteininterface (PPI) of Hsp90 and Cdc37, suggesting that interface inhibitors have an interesting drug development potential.

In order to identify inhibitors of the Hsp90/Cdc37 PPI, we have established a mammalian cell lysate-based, medium-throughput amenable split Renilla luciferase assay. This assay employs N-terminal and C-terminal fragments of Renillaluciferase fused to full-length human Hsp90 and Cdc37, respectively. We expect that our assay will allow for theidentification of novel Hsp90/Cdc37 interaction inhibitors. Such tool compounds will help to evaluate whether the toxicityprofile of Hsp90/Cdc37 PPI inhibitors is in general more favorable than that of ATP-competitive Hsp90 inhibitors. Furtherdevelopment of such tool compounds may lead to new classes of Hsp90 inhibitors with applications in cancer and otherdiseases.