PCI-34051 is a selective inhibitor of histone deacetylase 8 (HDAC8), an enzyme involved in the regulation of gene expression through chromatin remodeling. It is primarily used in research settings to study the role of HDAC8 in cellular processes such as proliferation, differentiation, and apoptosis. Due to its selectivity, PCI-34051 has been instrumental in investigating the potential of HDAC8 inhibition in treating cancers, particularly T-cell lymphomas and neuroblastoma. It has shown antiproliferative effects in certain cancer cell lines by inducing cell cycle arrest and promoting the expression of tumor suppressor genes. Additionally, it serves as a valuable tool compound in epigenetics research, helping to dissect the specific contributions of HDAC8 among other HDAC isoforms. Its application remains largely preclinical, supporting drug development and mechanistic studies in oncology and epigenetic therapy.