Didemnin B inhibits biological effects of tumor promoting phorbol esters on mouse skin, as well as phosphorylation of a 100 kD protein in mouse epidermis cytosol.

The immunosuppressive agent Didemnin B (DB) inhibits biological effects that are induced by topical application of phorbol esters to mouse skin as measured by mouse ear edema and the alkaline phosphatase activity of mouse epidermis. Furthermore, DB suppresses the phosphorylation in vitro of an epidermal cytosolic protein (p100). In these respects DB behaves like CsA, another immunosuppressive compound. Didemnin, however, does not bind to recently described CsA-binding sites.