Development of first-in-class USP7 inhibitors using structure-based design
Session type: Proffered paper sessions
Small molecule modulation of the MDM2/p53 axis is a major goal within oncology research. One strategy focuses on targeting ubiquitin specific protease 7 (USP7). USP7 controls stability of the E3 ligase MDM2, which is reflected in changes of its substrate p53. Depending on context, USP7 can also regulate p53 levels directly. A unique Industry-Academia Alliance led by CRUK Therapeutic Discovery Laboratories (CRUK-TDL) and Forma Therapeutics, which encompasses 4 academic centres, has focused on the development of highly specific deubiquitinase inhibitors with USP7 representing a high priority target. USP7 exhibits conformational plasticity between the apo-form and ubiquitin-bound states that can be exploited for drug development.
A high-throughput screening campaign targeting USP7 was carried out at Forma Therapeutics. Subsequent medicinal chemistry optimisation was driven by high resolution USP7-inhibitor X-ray structures and led to the development of highly specific inhibitors and to drug insensitive mutants of USP7. Specificity was profiled against a panel of deubiquitinase enzymes and by mass spectrometric analysis of target engagement in cell lysates and intact cells. Analyses of biological effects were carried out in tissue culture cells and in a MM.1S multiple myeloma xenograft mouse model.
A series of novel, potent and exquisitely selective reversible and covalent inhibitors of USP7 have been developed. We have found that these inhibitors specifically bind within the catalytic domain to the unique auto-inhibited apo-form state of USP7, leading to inhibition of its deubiquitinase activity. This provides a clear understanding of how selectivity within the USP family is achieved. We show compound-dependent modulation of established USP7 targets (e.g.MDM2/p53) in cell culture systems that is eliminated upon expression of compound resistant USP7. Modulation of p53 and tumour growth retardation is observed in a mouse xenograft model.
Our study provides a landmark in the development of a new targeting strategy for otherwise challenging oncology targets.