The non-degrading control was then used to treat MM.1S cells in direct comparison to the related PROTAC 1j. In comparison to 1j, the non-degrading control 1j-nc was not able to affect the protein levels of HDAC1 and 6 (Figure ), proving that covalent binding to DCAF11 is crucial for degradation. showed first promising effects. The phenotypic cell viability screening demonstrated that both PROTACs exhibited cytotoxicity against all tested cell lines (Table ). However, the effect was diminished in the solid cancer cell lines, particularly for U-87MG, in comparison to the multiple myeloma cell line MM.1S. As anticipated, the non-degrading control 1j-nc demonstrated no activity in MDA-MB-231, indicating that degradation is the underlying cause of cytotoxicity.