We conducted unbiased mass spectrometric experiments to evaluate the specificity of NCL-ZATAC#20. In these studies, HEK293T cells expressing GFP-NCL were treated with NCL-ZATAC#20. The result revealed the detection of more than 6000 proteins, among which there was a notable degradation of GFP-NCL, confirming the targeted action of NCL-ZATAC#20 against NCL protein.