Protein acetylation, a critical post-translational modification, regulates crucial cellular processes such as enzymatic activity, subcellular localization, and protein interactions. Moreover, it impacts cell signaling, turnover, differentiation, and survival. In this process, histone acetyltransferases (HATs) transfer acetyl groups (acetylation), and histone deacetylases (HDACs) remove them (deacetylation), thereby influencing both histone and non-histone proteins in various cellular functions. As essential epigenetic regulators, HDACs have captured significant attention through extensive research spanning multiple stages of tumor development over the past decades, with their dysregulation contributing to tumorigenesis. Mammalian HDACs, 18 subtypes in total, were categorized into four classes based on their sequences, structural features, and cellular localization, among which, class I (HDAC1, 2, 3 and 8), class II (HDAC4, 5, 7, 9, 6 and 10), and class IV (HDAC11) are Zn 2+ -dependent. In contrast, members of class III (Sirt1-7) depend on NAD + . Class II HDACs can be further divided into class IIa (HDAC4, 5, 7, and 9) and class IIb (HDAC6 and 10). Notably, the key characteristics of class IIb HDACs are that they are primarily located in the cytoplasm and have acetylated non-histone proteins as primary substrates. Substantial progress has been made to develop efficacious HDAC inhibitors (HDACi) to combat various HDACrelated diseases, including cancer. To date, four HDACi have been approved by the FDA for diverse cancer treatments. However, despite their promising impact on cancer growth, the widespread use of non-selective HDACi is associated with various side effects. This underscores the need for exploring more targeted approaches to achieve subtype-or class-selective HDAC inactivation, aiming for both efficacy and enhanced safety in therapeutic interventions. To this end, class IIb HDACs gained much attention.