We identified a series of 4-hydroxyquinolines bearing a C1 to C15 alkyl chain at the C2 position and a carbethoxy/carboxy group at the C3 position of the quinoline nucleus (MC compounds), endowed with selective inhibitory activity against the p300/CBP HAT enzymes. Enzyme inhibition was investigated using in vitro HAT assays and by western blot analysis of cellular lysates to examine the acetylation levels of histone H3 and alpha-tubulin. When tested in U937 cells, some compounds displayed pro-apoptotic or cytodifferentiating properties.