Variation in Photodynamic Efficacy during the Cellular Uptake of Two Phthalocyanine Photosensitizers

Abstract

A decrease in the efficacy of photodynamic therapy (PDT) with phthalocyanine photosensitizers was observed for lymphoblastic murine and human cell lines as the time between the addition of the photosensitizer, aluminum phthalocyanine (AlPc), to the culture medium and exposure to light was increased from 4 h to 18 h. The total intracellular concentration of photosensitizer did not decrease significantly during this 18 h interval. For the murine cell lines, the maximum cytotoxic and mutagenic effects were observed when the time between addition of the photosensitizer and irradiation was between 1 and 4 h. The time course of the variations in efficacy did not vary greatly from one murine cell line to another, even though the cell lines differ markedly in the extent of their cytotoxic and mutagenic response. The time course of the variation was similar for cytotoxicity and mutagenicity, as well as for the induction of DNA fragmentation. The human lymphoblastic cell line, WTK1, showed less variation in survival and mutability with time than did the murine cell lines. With Pc 4 (HOS~PCOS~[CH~],[CH,]~N[ CH,],) as the photosensitizer, the photocytotoxicity for murine L5178Y (LY)-Sl cells did not change significantly as the time between addition of Pc 4 and irradiation was increased from 2 to 18 h. However, the mutagenicity decreased by a factor of three during this interval. The mutagenicity of PDT with Pc 4 was much less in LY-S1 cells than that with AlPc. The results suggest that the variation in the efficacy observed for AIPc-induced photocytotoxicity is caused by changes in the intracellular distribution and/or the aggregation of the photosensitizer with time after its addition.

Apoptosis Mechanisms Related to the Increased Sensitivity of Jurkat T‐cells vs A431 Epidermoid Cells to Photodynamic Therapy with the Phthalocyanine Pc 4†‡

“…In a test of the stability of the uptake data, it was found that measurements at 2 and at 19 h after addition of Pc 4 to the culture medium did not differ by more than 5% for A431 cells and 20% for Jurkat cells. These data are in agreement with observations on Pc 4 uptake in other cells in which uptake reached a maximum in 1–2 h and did not change thereafter for the next 16–18 h (27). The average sizes of A431 and Jurkat cells were also measured against standard sizing beads.…”

Quantitative Analysis of Pc 4 Localization in Mouse Lymphoma (LY-R) Cells via Double-label Confocal Fluorescence Microscopy

“…LY-R cells were cultured as previously described (9,11,20,21) in Fischer's medium containing 0.1% Pluronic F68, 2 mM sodium pyruvate and 10% heat-inactivated horse serum. Cells were grown in a 25 cm 2 flask (Corning; Cambridge, MA) at 37ЊC and maintained at a cell density of 4-6 ϫ 10 5 cells/mL.…”

“…Determining the localization of a photosensitizer in a cell can help focus attention on the probable primary site(s) of initial damage by PDT with that photosensitizer. The phthalocyanine (Pc 4), HOSiPcOSi(CH 3 ) 2 (CH 2 ) 3 N(CH 3 ) 2 , is a second-generation PDT photosensitizer that is a highly efficient inducer of apoptosis in murine lymphoma cells and appears to activate a mitochondrial pathway of apoptosis (9)(10)(11). Therefore, we were interested in determining the subcellular localization of Pc 4 in these cells.…”

“…We studied the localization of the silicon phthalocyanine photosensitizer Pc 4 (15,16) in different organelles of LY-R cells. The hydrophobic nature of Pc 4 caused the molecule to bind to membranous organelles (3,6,9,(16)(17)(18) such as mitochondria and lysosomes which have been implied to be targets for photodynamic damage (3,10,16). Studies suggest that the distribution of the photosensitizer at different incubation times may affect the efficiency of PDT (2,6,9,19).…”

Secondary Reactive Oxygen Species Extend the Range of Photosensitization Effects in Cells: DNA Damage Produced Via Initial Membrane Photosensitization¶†

“…Most photosensitizers used in clinical PDT or in vitro PDT research do not localize in the nucleus, and as a consequence little attention has been paid to DNA damage in cellular systems. However, in the past few years, a number of studies have highlighted the potential of some PDT agents to cause nuclear alterations (48–50) and even mutagenesis (51–56). This article deals with a situation where DNA damage might not have been expected, i.e.…”