KS15 is an inhibitor of the interactions between cryptochromes (CRYs: CRY1 and CRY2) and the CLOCK:BMAL1 heterodimer . KS15 impairs the feedback actions of CRYs on E-box-dependent transcription (EC 50 =4.9 μM) by CLOCK:BMAL1 heterodimer, an indispensable transcriptional regulator of the mammalian circadian clock. Anti-proliferative activity .