Nonclinical teratogenicity safety assessment of CRBN-engaging targeted protein degraders: Points to consider

Targeted protein degraders (or degraders) are an emerging small molecule drug modality with transformative therapeutic potential. Currently, most degraders are developed for severe life-threatening disorders and engage the E3 ligase cereblon. One barrier to the broader use of degraders is the potential risk of embryofetal toxicity with cereblon-engaging degraders, exemplified by thalidomide. Thalidomide (and analogs, known as immunomodulatory drugs) binds cereblon and modifies its substrate repertoire, leading to degradation of intended and multiple unintended neosubstrates. Some cereblon-engaging degraders have been engineered to avoid the degradation of unintended neosubstrates implicated in teratogenicity, specifically SALL4. Mechanistic links between SALL4 degradation by thalidomide and human teratogenicity have been established; further, SALL4 degradation by thalidomide (and its analogs) has been linked to teratogenicity in susceptible nonclinical species. It is generally accepted that SALL4 degradation is unlikely to be the only mechanism of teratogenicity associated with thalidomide and its analogs. Currently, best practices to evaluate the teratogenicity risk of cereblon-engaging degraders have not been established. Here, we present points to consider in the teratogenicity safety assessment of cereblon-engaging degraders from the perspective of an IQ consortium working group.