The dibromotyrosine derivative (1′R,5′S,6′S)-2-(3′,5′-dibromo-1′,6′- dihydroxy-4′-oxocyclohex-2′-enyl) acetonitrile, isolated from Pseudoceratina sp., exhibited apoptotic activity by the activation of caspase-9 in leukemia K562 cells [22]. This evidence concerns the gene CASP9 and leukemia.