Nidulal, a novel inducer of differentiation of human promyelocytic leukemia cells from Nidula candida

Nidulal (1), a novel inducer of differentiation of human HL-60 promyelocytic leukemia cells, was isolated from fermentations of the basidiomycete Nidula candida together with low amounts of niduloic acid (2). Both compounds are bisabolane sesquiterpenes. Their structures were elucidated by spectroscopic methods. In reporter gene assays nidulal (1) preferentially activated the transcription factor complex AP-1-mediated expression of secreted alkaline phosphatase in COS-7 cells. In addition nidulal (1) and niduloic acid (2) exhibited weak cytotoxic and antibiotic activities.