Synthesis, characterization and activity of Antamanide and its analogues as inhibitors of the mitochondrial permeability transition pore

Antamanide (AA) is a non-toxic cyclic decapeptide which has the following amino acid sequence: c(Val-Pro-Pro-Ala-Phe-Phe-Pro-Pro-Phe-Phe). It was isolated in 1968 from the fungus Amanita phalloides. AA acts as an antidote in poisoning by this fungus, preventing the cellular accumulation of toxins, such as Phalloidin. It was also reported that AA inhibits tumor cell growth in vitro, displays an antitumor action in an animal model, and attenuates IL-2-induced multisystem organ edema. Like Cyclosporin A (CsA) and Cyclolinopeptide A, it has a powerful immunosuppressant activity. Moreover, as CsA and Cyclolinopeptide A, it interacts favorably with Cyclophilin-D (Cyp-D). Cyp-D is a mitochondrial protein that has a high sequence homology and essentially identical folding with other Cyclophilins. Cyp-D plays a key role in regulating the mitochondrial permeability transition pore (PTP), but it is not a component of the pore. The fact that the administration of CsA or the genetic ablation of Cyp-D leads to inhibition of PTP opening suggested Cyp-D as a potential pharmacological target for the treatment of diseases caused by dysregulation of the pore, such as muscular dystrophy. Studies on mice showed that ablation of Cyp-D protects the animal from cerebral ischemia and reperfusion injury and promotes recovery in diseases such as muscular dystrophy, autoimmune encephalomyelitis, and Alzheimer's disease. All these factors suggest that inhibiting Cyp-D can be a valuable therapeutic strategy. To assess its affinity for Cyp-D and to obtain valuable information about the structure-activity relationships, we synthesized AA and several of its monosubstituted derivatives and studied their effect on the PTP on isolated mitochondria or in whole cells.