Drugs currently used to treat cancer are non-selective, killing healthy as well as tumour cells. In this project, known anti-cancer drugs will be masked into an inactive (prodrug) form. Unlike other prodrugs, which slowly release the active drug distant from the tumour, our approach will enable control over when, where and how much active drug is released by using a 'two-drug' activation strategy. Firstly, the activating molecule, which is targeted to a tumour-specific receptor, will be administered. The prodrug will then be given, and only when it encounters the tumour-bound activator will the tumour-killing drug be released. This represents a new technology in tumour-targeted drug delivery by using a bioorthogonal chemical reaction that occurs only between the prodrug and its activator, providing complete tumour-selectivity. The pre-clinical data from this project will be used to evaluate the potential of this technology in the clinic.