XL-44

Proteolysis-targeting chimeras (PROTACs) and degraders have been developed against the hRpn13 fragment hRpn13^Pru that is present in various cancer types. Testing the performance of these hRpn13^Pru-targeting compounds in pharmacokinetic and efficacy studies has been stymied, however, by their poor solubility. Here, we develop a rapid and cost-effective platform to Screen and Characterize small molecule Nanosuspensions (SCaN). We discovered that the hRpn13^Pru degrader XL44 adopts a crystalline state, preventing its bioavailability. The first phase of SCaN screens vehicles to identify lead XL44 nanosuspension formulations based on particle size consistency, including in biorelevant media, while the second phase evaluates stability over time. The lead nanosuspensions are then advanced to the third phase of SCaN to assess their physical and colloidal stability. This pipeline allows the formulation of poorly soluble compounds for single-dose pharmacokinetic and pilot multidose tumor mouse studies. We additionally analyzed our XL44 formulation morphologically by atomic force microscopy to find that the XL44 nanoparticles are predominantly globular, with a small population of rod-like particles. Using the optimal nanosuspension determined by SCaN, XL44 slowed tumor growth in a myeloma xenograft model at 35% inhibition with a 48-72 mg/kg treatment regimen. This case study is the first in vivo demonstration that hRpn13^Pru-targeting degraders can inhibit tumor growth, and the efficacy shown here motivates the development of more potent hRpn13^Pru degraders. Broadly, our SCaN platform is designed for poorly soluble drug candidates to allow for pilot in vivo testing.