The present invention relates to small molecules interfering with the conformational space of the TONSL ARD occupied by the histone H4 tail. These small molecules targets the binding pocket ofTONSL encompassing the H4 residues Kl2- R23 and act by preventing or disrupting the binding of the H4 tail Kl2- R23 with the TONSL ARD via direct competition or via allosteric disruption of the binding pocket. The present inventors have identified and solved the structure of a histone reader domain ofTONSL termed the ARD (ankyrin repeat domain).