KPG-121 is a novel generation of Lenalidomide analogue. Results from in vivo metastatic castration resistant prostate cancer xenograft models demonstrated that KPG-121 at tested daily dose levels ranging from 1.0 mg/kg to 10 mg/kg in combination with Enzalutamide, Abiraterone Acetate, Apalutamide or Darolutamide significantly improved anti-tumor efficacy compared to the AR signaling inhibitors alone. In addition, KPG-121 showed favorable DMPK profiles and potentially manageable toxicity in pre-clinical IND enabling study.