Photodynamic inactivation of synchronized human cells in vitro in the presence of hematoporphyrin.

Dose-response curves for inactivation of synchronized cells from the human cell line NHK 3025 in the presence of hematoporphyrin and light are shown. Sensitivity toward photodynamic inactivation is increasing as the cells move in the cell cycle from G1 to mid-S. The increase is mostly due to a change in the extent of the shoulder of the dose-response curve at low doses. The quasithreshold dose (Dq) is high in early G1 and much lower in mid-S. No great variations were found in the slope (1/Do) of the dose-response curves at high doses. The shape of the dose-response curves indicates a higher capacity for repair of sublethal damage in the early part of the cell cycle than in the later stages.