Design of a Hyperpolarized Molecular Probe for Detection of Aminopeptidase N Activity

Aminopeptidase N (APN) is an important enzyme that is involved in tumor angiogenesis. Detection of APN activity can thus lead to early diagnosis and elucidation of tumor development. Although some molecular probes for APN have been developed, the detection of APN activity in opaque biological samples remains a challenge. To this end, we designed a hyperpolarized NMR probe [1-¹³C]Ala-NH₂ which satisfies the prerequisites for APN detection, namely, sufficient retention of the hyperpolarized state, a high reactivity to APN, and an APN-induced chemical shift change. The [1-¹³C]Ala-NH₂ probe allowed sensitive detection of APN activity using ¹³C NMR spectroscopy.