Mechanism of action of didemnin B, a depsipeptide from the sea.

With the brush border membrane vesicles prepared from the rat kidney cortex, didemnin B and its parent compound, didemnin A function neither as a K+-specific ionophore nor as an ionophore for Na+ ions while other depsipeptide antibiotics such as valinomycin and gramicidin promote transmembrane movement of K+ and Na+ ions, respectively. Didemnin B inhibits protein synthesis and DNA synthesis much more than RNA synthesis and is in general more potent than didemnin A. Time course studies reveal that the action of didemnin B is rapid and cannot be reversed after 2 h in contact with the cells. The inhibition of protein synthesis is almost superimposable to that of L1210 cells growth. DNA synthesis is also markedly inhibited. These results collectively suggest that didemnin B acts differently, at least in part, from other depsipeptide antibiotics and its biological effect is primarily mediated through its inhibition of protein synthesis and to a lesser extent its inhibition of DNA synthesis.