PHOTODAMAGING EFFECTS OF TETRAPHENYLPORPHYCENE IN A HUMAN CARCINOMA CELL-LINE

The photosensitizing effects of tetraphenylporphycene (TPPo) and light on HeLa cells, with emphasis on cell viability and the microtubular n etwork, have been investigated. The survival of the cells incubated wi th TPPo was dependent on both drug concentration and light dose. The i ntegrity of microtubules (MTs) was evaluated by immunofluorescence sta ining of alpha-tubulin. Interphasic and mitotic MTs were altered after 30 min of incubation with 5 mu M TPPo followed by light irradiation. The degree of damage depended on light exposure time: 3 or 15 min corr esponded to survival rates of similar to 50% or <5%, respectively. Sub lethal treatment led to the gradual accumulation of cells in metaphase . which caused an increase in the mitotic index (MI), with a maximum b eing found 6 h later. The number of cells in metaphase, as well as the MI, were within control values 24 h after sublethal photodynamic trea tment. Lethal treatment provoked irreversible damage of interphasic an d mitotic MTs. In addition, cell surface modifications such as bleb pr ojections of the plasma membrane were also observed immediately after lethal treatment. It is concluded that both cellular structures, plasm a membrane and MTs, constitute important targets for the phototoxic ac tion of TPPo.