**3.3 Cancer selective photodynamic action of phosphorus(V) porphyrin photosensitizers**

Above mentioned phosphorus(V) porphyrins, **Por8**, **Por9**, and **Por12**, exhibited the cancer cell selective toxicity under visible light irradiation [46].

**Figure 4.**

*Structures of Por8, Por9, and Por12, and their IC50 values for HeLa cells under photoirradiation [46].*

Photocytotoxicity to HeLa cells by these porphyrins are the following order: **Por9** > **Por12** > **Por8** in the condition of previous report (**Figure 4**) [46]. Although the half maximal inhibitory concentration (IC50) value for **Por8** is largest (least phototoxicity) in the three phosphorus(V) porphyrins, its photocytotoxicity to cancer cells is sufficiently high. Furthermore, **Por8** did not exhibit photocytotoxicity to HaCaT cells, cultured human skin cells (normal cell model). **Por9** and **Por12** exhibited phototoxicity to HaCaT cells, however, these IC50 value were significantly larger than those for HeLa cells and cellular DNA damage in HaCat cells were not observed. These three phosphorus(V) porphyrins demonstrated significant PDT effects on mice tumor models [46]. The observed PDT effects by these porphyrins are almost the same, and are comparable with that of talaporfin sodium. These results suggest the cancer selectivity of **Por8**, **Por9**, and **Por12**, and lower carcinogenic risk to normal cells. Specifically, **Por8**, of which the redox potential is most advantageous for the electron transfer-mediated biomolecule oxidation, demonstrated the highest cancer-selectivity and significant PDT effect under irradiation with longwavelength visible light.
