A synthetic heterocyclic carboxaldehyde thiosemicarbazone with potential antineoplastic activity. Triapine inhibits the enzyme ribonucleotide reductase, resulting in the inhibition of the conversion of ribonucleoside diphosphates to deoxyribonucleotides necessary for DNA synthesis. This agent has been shown to inhibit tumor growth in vitro. OR A substance being studied in the treatment of cancer. It is a type of ribonucleotide reductase inhibitor. Also called 3-aminopyridine-2-carboxaldehyde thiosemicarbazone and 3-AP.