Mass-spectrometry-based proteomics analyses in prostate cancer cells confirmed that CBPD-409 specifically degraded p300 and CBP (Fig. 3d and Extended Data Fig. 3h) without affecting other bromodomain proteins, including bromodomain and extraterminal protein (BET) family members39 (Extended Data Fig. 3i,j) or known CRBN neo-substrates, including G1 to S phase transition 1 (GSPT1) and Ikaros40 (Extended Data Fig. 3k). This evidence concerns the gene GSPT1 and prostate carcinoma.