Spectrofluorometric measurements of the dispersion state of pyrenedodecanoic acid and its uptake by cultured cells and liposomes

Photosensitization of human bladder carcinoma cells by pyrene-dodecanoic acid: quantitative analysis of the cytotoxicity

The effects of photochemotherapy with the fluorescent fatty acid pyrenedodecanoic acid (P12) and long-wavelength ultraviolet (UVA) light on cells derived from human bladder carcinoma were studied. Exposure of these anchorage-dependent cells to P12 either in monolayers of adherent cells or in suspension resulted in a time-related uptake of P12 and its incorporation into the cells' neutral and phospholipids. The uptake and localization of P12 was visualized with fluorescence microscopy and the distribution of the cell population with respect to P12 uptake was analyzed by flow cytometry. Irradiation of P12-containing monolayers of bladder carcinoma cells with UVA light resulted in cell killing. But, on microscopic examination no apparent cell lysis was detected, and since digestion with trypsin did not result in the dispersion of the monolayers it was impossible to assess toxicity by cell count. Alternative procedures were therefore used, and the following cell parameters were determined: (a) cellular uptake or release of chromate; (b) ability of cells to re-adhere to the substratum; and (c) the long-range proliferation potential. The combined inhibitory effect of photoirradiation on cell adherence and on their proliferative potential was utilized for determining reductions of up to 7 log in cell viability. The results obtained with five independently established in vitro bladder carcinoma cell lines indicated that these cells are susceptible to P12-induced photosensitization, suggesting that bladder malignancies might be potential candidates for pyrene-induced photochemotherapy.

Pyrene butanol--an efficient, selective and non-metabolized photosensitizing agent for human myeloid leukemia cells

Methods for ex vivo purging of neoplastic cells from harvested marrow are being developed to increase the efficacy of autologous transplantation. One approach is selective photosensitization, using sensitizing compounds and light radiation. Pyrene-containing fatty acids and lipids are potent photosensitizers, e.g. 12-(1-pyrene)dodecanoic acid (P12), is taken up preferentially by leukemic cells and undergo photoexcitation when exposed to long wave ultra-violet light, resulting in selective killing of leukemic cells. These compounds are incorporated into the neutral- and phospho-lipids of the cells. The presence of intracellular pyrene-linked lipids might present a potential hazard in applying these agents for clinical use. We have, therefore, studied a series of other pyrene-linked compounds with the objective of finding a non-metabolizable photosensitizing agent that can be easily removed from the cells. In the present paper we report the results with pyrene butanol (P4-OH), a pyrene linked short-chain alcohol. When compared to P12, P4-OH was found to be taken up by cells most rapidly and reached saturation within minutes. It did not undergo any metabolism and washing the cells with serum-containing salt solutions removed practically all the P4-OH. This compound was found to be an efficient photosensitizer (in terms of concentrations and time of incubation with the cells) and selective to leukemic cells--it caused a 99% reduction in leukemic clonogenic cells under conditions that normal hemopoietic progenitors remained almost intact. These properties make P4-OH a potential photosensitizer for clinical application.

Pyrene eximer mapping in cultured fibroblasts by ratio imaging and time-resolved microscopy

The kinetics of pyrene eximer formation provide a measure of lateral diffusibility in bilayer membranes. Swiss 3T3 fibroblasts were labeled with pyrene, pyrenedecanoic acid (PDA) and 1,3-bis(1 pyrene) propane (BPP) by incubation in the presence of Pluronic F127. Single-cell emission spectra obtained by epifluorescence microscopy (excitation 350 nm) with photodiode array detection showed monomer (380-420 nm) and eximer (475 nm) peaks. The eximer-to-monomer fluorescence ratio (E/M) increased with increasing temperature and loading time. Time-resolved microscopy studies of fibroblasts labeled with PDA for 15 min gave monomer and eximer lifetimes of 101 and 78 ns, respectively, with a monomer-to-eximer conversion rate of 0.02 ns-1. E/M ratio images were obtained with a microchannel plate intensifier and CCD camera at 350-nm excitation and 405 +/- 5 nm (monomer) and greater than 470-nm (eximer) emission wavelengths. E/M ratios of PDA showed spatial variation across the cell with highest ratios at the peripheral plasma membrane. These results establish the methodology to label cells with pyrene eximer-forming probes and to image eximer distributions in membranes of intact cultured cells. Eximer-to-monomer fluorescence ratios are sensitive to maneuvers that alter the membrane physical state and should be of utility in examining the cellular regulation of membrane fluidity.

Analysis of cellular heterogeneity in the response of human leukemic cells to photosensitization induced by pyrene-containing fatty acid

Incubation of cells with 12-(1-pyrene) dodecanoic acid (P12) followed by irradiation with ultraviolet light at 366 nm (UVA) resulted in cytotoxicity. We compared the photosensitivity to UVA irradiation of various human myelo-monocytic leukemic cell lines, their intra- and inter-clonal variability and correlated their photosensitivity to P12-uptake and metabolism. The fluorescence properties of pyrene were utilized for flow cytometric analysis of cell distribution with respect to P12-uptake as well as for sorting subpopulations differing in their fluorescence. Spectrofluorometric analysis of the total cell-associated fluorescence and of the cellular lipids-associated fluorescence were also carried out. Considerable heterogeneity in P12-uptake and photosensitivity was found not only among cell lines, but also in the response of different clones and among the individual cells in specific clonal populations. Within a clone, photosensitivity was related to the amount of P12 taken up by the individual cells, while among different cell lines and their clones the photosensitivity was correlated with the proportion of cellular pyrene-linked phospholipids. The larger the fraction of pyrene-linked phospholipids within the cell--the more sensitive it was to UVA-irradiation. Photosensitivity could be affected by changing the proportion of cellular pyrene-linked phospholipids. Cells treated with cAMP showed an increase in total P12-uptake, but the proportion of pyrene-linked phospholipids was reduced, resulting in lower photosensitivity. These findings, demonstrating that by manipulating lipid metabolism photosensitivity can be modified, may prove useful in a clinical setting for selective photosensitization of malignant cells.