Our group has reported recently about the very promising in vitro light-induced anticancer properties of novel tetraplatinated porphyrins 1.¹ This family of platinum-porphyrin conjugates 1 had only minor dark toxicity, however upon visible light irradiation (420 or 575 nm), IC₅₀ values down to 19 ± 4 nM could be observed. These values correspond to an excellent phototoxic index (PI = IC₅₀ dark / IC₅₀ light) of greater than 5000.

We have now started to study similar systems that contain a metal in the central position of the porphyrin (2 and 3). We will discuss the influence of the metal on the singlet oxygen yield, cellular dark and (photo)toxicity as well as cellular localisation. For the latter we employed the isotopically labelled ⁶⁷Zn complex 2b in order to determine, by ICP-MS, the cellular distribution of ⁶⁷Zn and platinum, which in turn allowed us to study the stability of the platinum - pyridine nitrogen bond within the cells. We included the copper(II) 3, since we previously discovered the first phototoxic copper(II) complex of a porphyrin.²

Acknowledgements

We thank for financial support by the University of Zurich and the Swiss National Science Foundation.

[1] Naik, A.; Rubbiani, R.; Gasser, G.; Spingler, B. Angew. Chem. Int. Ed. 2014, 53, 6938.
[2] Antoni, P. M.; Naik, A.; Albert, I.; Rubbiani, R.; Gupta, S.; Ruiz-Sanchez, P.; Munikorn, P.; Mateos, J. M.; Luginbuehl, V.; Thamyongkit, P.; Ziegler, U.; Gasser, G.; Jeschke, G.; Spingler, B. Chem. Eur. J. 2015, 21, 1179.