[RhacacCOD]°, on Ehrlich ascites and Li210 leukemia growth and on the incorporation of labeled precursors into macromolecules of the tumor cells. RhacacCOD is structur ally related to a series of rhodium derivatives for which anhihumor

Two omganometallic complexes, acetylacetonate-1 ,5-cy clooctadienerhodium(l) ([RhacacCOD]°) and cis-dichloro tetrakisdimethylsulfoxide ruthenium(lI) ([cis-Ru(Il)(DMSO)4C12]°), have been examined for antitumor activity. Rhacac COD had an activity comparable with that of cis-diammine dichloroplatinum(ll) (cis-PDD) against Ehnlich ascites carci noma, yielding 100% cures at two dosages, whereas the comparative activity of [cis-Ru(lI)(DMSO)4Cl2]°was slightly lower. Only cis-PDD and [cis-Ru(II)(DMSO)4CI2]°had any significant activity against L1210 leukemia. The histological damage caused by the compounds tested was moderate and was virtually absent for [RhacacCODJ°,on intestinal mucosa and spleen, when compared with that of cis-PDD. Labeled precursor incorpo ration into macromolecules of tumor cells showed a selec hive depression of unidine incorporation for [RhacacCOD]. [cis-Ru(ll)(DMSO)4CI2]°,however, caused a similar inhibi lion of incorporation of thymidine, unidine, and leucine at the highest dosage tested, but no such effects were ob served at the two lower dosages that were still therapeuti cally useful. Our findings indicate that, in the experimental systems used, [RhacacCODJ°and Icis-Ru(ll)(DMSO)4Clz]°have a therapeutic efficacy better than or equal ho that displayed by cis-PDD, and that they may have a different mode of action.