Calphostins (UCN-1028), novel and specific inhibitors of protein kinase C. I. Fermentation, isolation, physico-chemical properties and biological activities

A novel complex of calphostin (UCN-1028), which specifically inhibits protein kinase C (PKC) has been isolated from the culture broth of a fungi Cladosporium cladosporioides. Purification of individual components was carried out by silica gel, non-porus resin Diaion HP-20SS and Sephadex LH-20 chromatography, leading to isolation of five closely related components. A, B, C, D and I. Calphostins showed cytotoxic activities against various tumor cells, and these cytotoxicities were proportional to their inhibitory activities against PKC.