[Mode of action of new antitumor compounds]

The antitumoral agents PR toxin, bouvardin and grandilactones A and B inhibit the growth of HeLa cells, and abolish polyphenylaline synthesis by polyuridylic acid in acellular eukaryotic systemns. However, only bouvardin and the PR toxin inhibit polypeptide synthesis in polysomes using endogenous m-RNA. In addition, grandilactones A and B inhibit the "fragment" reaction, which indicates that they affect specifically peptide bond formation, and the lack of effect on polysomes of these compounds would be due to the fact that, in polysomes, the substrate is bound to either the donor on the acceptor site. Apparently, the PR toxin acts by blocking the enzymatic binding to 80 S ribosomes of (3H)phenylalanyl-tRNA. The inhibitory action of bouvardin seems to be result of the selective blocking of peptidyl-tRNA translocation dependent on elongation factor EF-2 and GTP.