P005091 (P5091) is a selective and potent inhibitor of ubiquitin-specific protease 7 (USP7) with EC50 of 4.2 μM.

USP7:4.2 μM

P5091 demonstrates synergistic anti-multiple myeloma (anti-MM) activity when used in combination with Lenalidomide, the HDAC inhibitor SAHA, or Dexamethasone. In animal tumor models, P5091 is well-tolerated, inhibits tumor growth, and prolongs survival.

P5091 exhibits potent, specific, and selective deubiquitinating (deubiquitinase) activity against USP7. Conversely, P5091 does not inhibit other tested DUBs or proteases from different families (EC50 >100 mM). It decreases HDM2 and HDMX levels while upregulating p53 and p21. P5091-induced cytotoxicity is partly mediated via the HDM2-p21 signaling axis, and despite the upregulation of p53 following P5091 treatment, its cytotoxic effects do not depend on p53. P5091 concentration-dependently inhibits USP7 tagged with HA-UbVME and dose-dependently inhibits USP7-mediated disassembly of ultra-high molecular weight ubiquitin chains. Moreover, P5091 inhibits the breakdown of polyK48-linked ubiquitin chains specifically by USP7 rather than USP2 or USP8. It suppresses USP7 deubiquitinase activity in MM cells without inhibiting protease activities and overcomes bone marrow stromal cell-induced MM cell growth.

Recombinant enzymes in 20 mM Tris-HCl (pH 8.0), 2 mM CaCl2, and 2 mM β-mercaptoethanol are incubated with dose ranges of P005091 for 30 min in a 96-well plate before the addition of Ub-PLA2 and NBD C6-HPC or Ub-EKL and EKL substrate. The liberation of a fluorescent product within the linear range of the assay is monitored using a Perkin Elmer Envision fluorescence plate reader. Vehicle (2% [v/v] DMSO) and 10 mM N-ethylmaleimide (NEM) are included as controls.

Animal Models: CB-17 SCID-mice are subcutaneously inoculated with MM.1S, ARP-1, or RPMI-8226 cells in 100 μL of serum free RPMI-1640 medium. Formulation: P005091 is dissolved in 4% NMP(N-methyl-2-Pyrrolidone), 4% Tween-80, and 92% Milli-Q water at a final concentration of 2 mg/mL.