There is increasing interest in developing specific inhibitors to various deubiquitylases (DUBs) which are enzymes that cleave ubiquitin from substrates and are implicated in disease. Much focus has been on one of these DUBs termed ubiquitin-specific protease-7 (USP7) which regulates stability of the p53 tumour suppressor critical for tumour cell survival. Inhibitors of USP7 have the potential to stabilize p53 and other tumour suppressors and therefore inhibit tumour growth.

There are ~100 deubiquitylases and many of these have highly similar structures and catalytic sites. Because of this, most inhibitors generated up to now are not selective and invariably inhibit a large number of other DUBs. To help with the development of DUB inhibitors, the MRC PPU through work originally pioneered by Maria Stella Ritorto, Matthias Trost and Dario Alessi and more recently Virginia de Cesare and members of the DUB profiling team including Ryan Traynor, developed a facile and quantitative mass spectrometry based assay to assess the potency and specificity of DUB inhibitors termed the MALDI-TOF DUB assay. The assay allows the potency and selectivity of DUB inhibitors to be characterized by testing them against a panel that currently consists of around 32 DUBs.

Using our MALDI-TOF DUB assay, we were able to demonstrate that two potent USP7 inhibitors elaborated by Genentech, termed GNE-6640 and GNE-6776 were highly selective for USP7 and did not significantly inhibit any other DUB on our panel. Genentech went on to elegantly demonstrate that the selectivity of these compounds is due to their ability to attenuate ubiquitin binding to USP7. They also demonstrated that USP7 inhibitors induced tumour cell death and enhanced cytotoxicity with chemotherapeutic agents, validating the concept that USP7 inhibitors might have benefit in treating cancer.

To read the paper describing the USP7 inhibitors click here.

To learn more about our DUB profiling technology and the DUB screening services we offer click here.