In order to analyze the selectivity profile of AP1 by an orthogonal method, we performed quantitative proteomics analysis. To this end, MM.1S cells were treated for 6 h with 1 µM of AP1, tubastatin A, and To further investigate the proteome-wide degradation specificity of AP1, we performed quantitative proteomics analysis in MOLT-4 cells. In this experiment, HDAC6, but not HDAC10, could be quantified.