Tosedostat is a synthetic aminopeptidase inhibitor. Structurally, it is a dipeptide mimetic, specifically a phosphonic acid analogue of alanine-phenylalanine (Ala-Phe). This design allows it to act as a potent and selective inhibitor of multiple aminopeptidases. Its primary application is as an investigational anti-cancer agent (API). Tosedostat functions by inhibiting key intracellular aminopeptidases, particularly those involved in the final stages of protein degradation. This inhibition leads to an accumulation of amino acid-deprived proteins, which triggers an unfolded protein response and ultimately induces apoptosis (programmed cell death) in tumor cells. It has been evaluated in clinical trials for the treatment of acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS). As a peptide-based therapeutic candidate, it falls under the category of peptidomimetics. Its development highlights the strategy of targeting amino acid metabolism within cancer cells.