An orally bioavailable, small molecule inhibitor of the highly conserved bromodomains of the histone acetyltransferase (HAT) paralogs, p300 (E1A-associated protein p300; p300 HAT) and CREB binding protein (CBP), with potential antineoplastic activity. Upon oral administration, inobrodib selectively and reversibly binds to the bromodomains of p300 and CBP. This disrupts the acetylation of histones and other proteins and prevents the co-activation of key transcription factors that contribute to tumor progression including the androgen receptor (AR), androgen receptor splice variants (AR-SV), hypoxia-inducible factor 1-alpha (HIF-1-alpha) and Myc proto-oncogene protein (c-Myc). The HAT paralogs p300 and CBP are key transcriptional co-activators that are essential for a multitude of cellular processes and are implicated in the progression and therapeutic resistance of certain cancers.