Cancer is the leading cause of death in New Zealand and there is an unmet global need for new therapies. One promising new treatment utilises biological agents, such as tumour-targeting viruses, to deliver enzymes to tumours. These enzymes "switch on" inactive non-toxic prodrugs, which become potent chemotherapeutic toxins within the tumour. This strategy has yielded promising results in early-stage clinical trials, but further development has been limited by several issues. The objective of this research is to address such limitations by engineering superior enzymes for use in cancer therapy. Classic molecular biology techniques, including enzyme cloning, expression and purification, will be combined with specialised molecular biology techniques (such as metagenomic screening and protein engineering), to characterise, evolve and analyse enzymes for desirable therapeutic qualities. This research has the potential to aid the development of improved cancer therapies which will have significant influence in both economic and health systems.