Copies of full items can be used for personal research or study, educational, or not-forprofit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. (1) is potently cytotoxic to cancer cells when irradiated with visible (blue) light. We show that the acute photocytotoxicity can be switched off by low doses (500 μM) of the amino acid L-tryptophan. EPR and NMR spectroscopic experiments using spin traps show that L-Trp quenches the formation of azidyl radicals, probably by acting as an electron donor. L-Trp is wellknown as a mediator of electron transfer between distant electron acceptor/donor centers in proteins, and such properties may make the free amino acid clinically useful for controlling the activity of photochemotherapeutic azido Pt IV drugs. Since previous work has demonstrated the ability of photoactivated 1 to platinate DNA, this suggests that the high potency of such photoactive platinum complexes is related to their dual attack on cancer cells by radicals and Pt II photoproducts.

The most widely used anticancer drugs are platinum-based. Their efficacy might be improved by carriers which can transport large numbers of Pt centres, shield the drug from premature activation, and/or deliver Pt specifically to cancer cells using vectors which recognise specific targets. We describe recent progress using functionalized carbon nanotubes (CNTs) and nanorods, hollow Prussian blue (HPB), magnetic iron oxide and gold nanoparticles, liposomes, nanogels and polymers, as well as active targeting by conjugation to biodegradable proteins and peptides (e.g. EGF, heparin, herceptin, somatostatin and TAT). Spatially targeted activation of Pt(IV) prodrugs using light is also a promising approach. Interestingly, use of these new delivery and targeting systems for platinum drugs can lead to species with unusual reactivity which can kill cancer cells by new mechanisms.

No abstract