The iron(III) and copper(II) complexes of adriamycin promote the hydrolysis of the cardioprotective agent ICRF-187 ((+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane).

ICRF-187 ((+)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane) has shown promise (Speyer et al., N. Engl. J. Med. 319, 745 (1988] as a cardioprotective agent against what may be an iron-based adriamycin-induced cardiotoxicity. ICRF-187, which is membrane permeable, likely exerts its action through its rings-opened hydrolysis product which has a structure similar to EDTA and which, likewise, strongly binds metal ions. Both Fe3(+)-adriamycin and Cu2(+)-adriamycin reacted directly with ICRF-187, promoting a ring-opening hydrolysis of ICRF-187 that resulted in the displacement of the metal ion from its complex with adriamycin. Thus ICRF-187 can be considered to be acting as a "suicide protective agent" in its reaction with metal ion-adriamycin complexes. That this metal ion complex-promoted hydrolysis was preceded by mixed ligand complex formation is evidenced by the fact that the first-order rate constant for loss of metal ion from the adriamycin complex exhibits saturation behaviour at high ICRF-187 concentrations. Also direct spectroscopic evidence was obtained both for a Cu2(+)-adriamycin-ICRF-187 mixed ligand complex and a Cu2+ (ICRF-187)2 complex. The Fe3(+)-adriamycin complex inactivates the cytochrome c oxidase and NADH cytochrome c reductase activity on submitochondrial particles. The protection that ICRF-187 affords against this loss of activity may be explained both on the basis of simple Fe3+ removal from Fe3(+)-adriamycin and also on formation of a less active Fe3(+)-adriamycin-ICRF-187 mixed ligand complex.