TKT and cancer: TG6002 is a VV from the Copenhagen strain that is deleted of the TK and the ribonucleotide reductase (RR) genes and expresses the suicide gene FCU1. 10As TK, RR is a key enzyme in the supply chain of deoxyribonucleoside triphosphates (dNTPs) for DNA replication and is often overexpressed in cancer.11