Disclosed is an oligopeptidic compound capable of interacting with proliferating cell nuclear antigen (PCNA), wherein the compound comprises a PCNA interacting motif which is: (SEQ ID NO. 28) [K/R]-[F/Y/W]-[L/I/V/A/M]-[L/I/V/A/M]-[K/R]; wherein the oligopeptidic compound has 9-70 subunits and comprises at least one signal sequence, wherein the signal sequence is a nuclear localization signal sequence and/or a cell penetrating signal sequence and wherein in said compound a PCNA interacting motif is N-terminal to a signal sequence. Also disclosed are methods of treatment of a disorder or condition where it is desirable to inhibit the growth of cells, or a method of treatment which involves cytostatic therapy, or a method of treatment of inflammation said method comprising administering the oligopeptidic compound to a subject in need thereof.