BRD4 and osteosarcoma: The PROTACs were initially screened in U2OS osteosarcoma cells due to their known sensitivity to BRD4 inhibition, degradation, and MAGEA11 expression, confirmed via western blot (Supplementary Figure S1).25, 28, 29 The PROTACs were screened in a 24 hour, 4-point titration from 10 - 0.01 μM concentrations.