In the next step, we investigated whether this target engagement translates into degradation of multiple HDAC isoforms. HDAC1, 2, 4 and 6 levels were determined by immunoblot analysis of MM.1S cell lysates and the CRBN-recruiting PROTAC A6 was used as control. The immunoblot analysis confirmed the automated Simple Western™ immunoassay results, as 1j showed most pronounced degradation of all tested HDAC isoforms (Figure ). In detail, the strongest degradation was observed for HDAC1 (90%) by 1j, while the degradation of HDAC2, 4 and 6 ranged from 71-76%. Compound 2, although slightly less efficient, also degraded HDAC1 most successfully (74%) followed by HDAC2 (54%), while HDAC4 (40%) and HDAC6 (26%) were also degraded, but to a lesser extent. In contrast, A6 selectively degraded HDAC6 without significant effects on the other HDAC isoforms, as previously reported. By utilizing DCAF11 instead of CRBN for HDAC degradation, 1j and 2 are able to broaden the scope of degraded HDAC isoforms, degrading not only HDAC6 but also HDAC1, 2, 4 and 6. In addition, the degradation pattern of This analysis revealed less differences between the DCAF11-recruiting PROTACs and the HDACi.