Photoinactivation of Chinese hamster cells by hematoporphyrin derivative and red light

Preliminary results of interstitial motexafin lutetium-mediated PDT for prostate cancer

BACKGROUND AND OBJECTIVES

Interstitial photodynamic therapy (PDT) is an emerging modality for the treatment of solid organ disease. Our group at the University of Pennsylvania has performed extensive studies that demonstrate the feasibility of interstitial PDT for prostate cancer. Our preclinical and clinical experience is herein detailed.

STUDY DESIGN/MATERIALS AND METHODS

We have treated 16 canines in preclinical studies, and 16 human subjects in a Phase I study, using motexafin lutetium-mediated PDT for recurrent prostate adenocarcinoma. Dosimetry of light fluence, drug level and oxygen distribution for these patients were performed.

RESULTS

We demonstrate the safe and comprehensive treatment of the prostate using PDT. However, there is significant variability in the dose distribution and the subsequent tissue necrosis throughout the prostate.

CONCLUSIONS

PDT is an attractive option for the treatment of prostate adenocarcinoma. However, the observed variation in PDT dose distribution translates into uncertain therapeutic reproducibility. Our future focus will be on the development of an integrated system that is able to both detect and compensate for dose variations in real-time, in order to deliver a consistent overall PDT dose distribution.

Enhanced photodynamic effects using fractionated laser light

Photodynamic eradication of tumour cells depends on the presence of a photosensitizer and light delivery to the cells. The present study investigated the influence of fractionated light (on-off mode) on cell killing as documented by a colony-forming assay. Photosensitizers were m-THPC (ethanol soluble, Foscan) and m-THPC-MD (water soluble, both from Scotia Pharmaceuticals, Guildford, UK). Fractionated laser light at a wavelength of 652 nm with a light duration of 0.05 s was more effective than continuous illumination at the same power density for both photosensitizers. We propose that fractionated laser light is more toxic due to short phases of recovery during the dark intervals, probably resulting in more singlet oxygen under these conditions. By use of Foscan, for example, and fractionated laser light, a similar effect is expected for the treatment of solid tumours. In this case we expect improvements in photodynamic therapy (PDT) for patients by lowering the concentrations of photosensitizer and/or by reducing the applied light dose.

Cooperative effects of photodynamic treatment of cells in microcolonies

Microcolonies of 2-8 Madison-Darby canine kidney cells (MDCK II) and Chinese hamster lung fibroblasts (V79) cells were incubated with the photosensitizer Photofrin and exposed to light, and the resulting number of dead cells per colony was determined. The distribution of this number was found to be incompatible with the assumption that cells are inactivated independently. The experimental distributions were significantly different from the binomial distribution expected from this assumption, but in accordance with a model in which an inactivated cell can inactivate adjacent cells with a certain probability. These findings are contrary to the common view that damage caused by radiation is limited to the cell in which the primary damage takes place. Our findings clearly indicate some kind of cooperativity between cells treated with Photofrin and light.

Photodynamic therapy of human bladder carcinoma cells in vitro with pH-sensitive liposomes as carriers for 9-acetoxy-tetra-n-propylporphycene

In vitro experiments were performed on human bladder carcinoma cells to evaluate the efficiency of the recently synthesized photosensitizer 9-acetoxy-tetra-n-propylporphycene (ATPPn) for photodynamic therapy. To improve cytoplasmic delivery of this hydrophobic compound, we prepared pH-sensitive liposomes composed of phosphatidylethanolamine (PE) and cholesteryl hemisuccinate (CHEMS) in comparison with pH-insensitive liposomes consisting of phosphatidylcholine (PC) and CHEMS. Dynamic light scattering measurements were used to monitor the acid-induced liposome destabilization. After incubation with liposome-bound ATPPn, bladder carcinoma cells were irradiated by a dye laser with increasing light fluence rates from 1 to 48 J/cm2. The photodynamic effects were then assessed from cell survival curves. No dark or phospholipid toxicity was measured for 2 micrograms ATPPn/1.5 ml medium. Qualitative cellular uptake of ATPPn was determined by fluorescence microscopy, while photodamage was elucidated by transmission and scanning electron microscopy. Absorption spectra performed up to 42 days revealed changes in shape for the pH-sensitive liposomes after storage at room temperature. ATPPn was proved to be an encouraging photosensitizer, capable of reducing cell survival to 0.1% after short-term incubation of 60 min with a drug dose of 2 micrograms ATPPn/1.5 ml medium. Although pH-sensitive PE/CHEMS liposomes showed significantly (P < 0.05) more photokilling effects at 24 J/cm2 and 48 J/cm2, no further advantages over non-pH-sensitive PC/CHEMS liposomes were found.

Flow cytometric analysis of intracellular hematoporphyrin derivative in human tumor cells and multicellular spheroids

Flow cytometry (FCM) has been used to investigate the intracellular fluorescence of hematoporphyrin derivative (HPD) in monolayer and spheroid cultures of WiDr cells. For exponentially-growing monolayer cultures mean cellular fluorescence was directly proportion to the external HPD levels in the range 5-100 micrograms ml-1 (r = 0.99). Heterogeneity of cellular fluorescence was quantified by determining the ratio of the fluorescence value below which were observed values for 98% of the cell population compared to the fluorescence value for 2%. In exponentially-growing cultures, decreasing levels of HPD in the medium led to an increase in the 98:2% ratio, i.e. an increase in heterogeneity of intracellular drug levels. The growth of cells as multicellular spheroids confers a spheroid-size-dependent resistance to photodynamic treatment. With increasing spheroid size (100, 250, 500, 750 and 1000 microns diam.) there was a decrease in mean intracellular HPD levels and a large linear increase in the 98:2% ratio (r = 0.94).

Size-dependent resistance of human tumour spheroids to photodynamic treatment

Spheroids derived from the human colon adenocarcinoma cell line, WiDr, were exposed to 10 micrograms ml-1 Photofrin II and irradiated with light (700 nm, 50 mW cm-2). Compared with exponentially growing monolayer cultures, cells in spheroids of 100, 250 and 500 microns diameter were respectively 1.8, 2.5 and 22-fold less sensitive. The small resistance of plateau-phase cultures (1.3-fold) was insufficient to account for this marked spheroid size-dependent resistance. For monolayer cultures and for spheroids of 100 and 250 microns diameter, the results were the same whether irradiations were carried out pre- or post-trypsinisation. However, there was a difference for the largest spheroid size: when irradiations were carried out pre-trypsinisation, spheroids were more resistant than when irradiations were given post-trypsinisation. Drug extraction studies showed that there was no difference in the average drug uptake between cultures of exponentially growing or plateau-phase cells, and 100 microns diameter spheroids while 250 and 500 microns diameter spheroids took up proportionally 0.5 and 0.4 as much drug. Cell contact effects, drug heterogeneity between cells, hypoxia and problems in drug penetration are suggested as possible reasons for the resistance of large spheroids to photodynamic treatment.

In vitro photosensitization I. Cellular uptake and subcellular localization of mono-L-aspartyl chlorin e6, chloro-aluminum sulfonated phthalocyanine, and photofrin II

The mechanisms of cellular uptake, subcellular localization, and cellular retention kinetics of the photosensitizers photofrin II (PfII), mono-L-aspartyl chlorin e6 (MACE), and chloro-aluminum sulfonated phthalocyanine (CASPc) are reported in this paper. Each photosensitizer's cellular uptake mechanism was determined by preferentially inhibiting endocytosis by chilling cells to 2 degrees C, while allowing diffusion across the membrane. Subcellular localization was studied by computer-enhanced low-light level video fluorescence microscopy, while flow cytometry was used to determine uptake and retention kinetics. The results indicate that PfII enters the cell primarily by diffusion across the membrane, whereas MACE and CASPc enter the cell through endocytosis.

The effect of fractionation of light treatment on necrosis and vascular function of normal skin following photodynamic therapy

Sparing of normal tissue, mouse tail skin, by fractionation of light treatment in photodynamic therapy has been demonstrated in BDF1 mice injected with 2 mg tetrasodium-meso-tetra(4-sulphophenyl)porphine dodecahydrate i.v. When the time between 2 fractions of 67.5 J cm-2 and 90 J cm-2 was increased to 2 and 4 days respectively the incidence of necrosis fell to that expected after a single fraction. Blood flow in the tail skin 5 days after the second light fraction, as measured by the clearance of an intradermally injected solution of 133xenon in 0.9% saline, returned to control values when the time between 2 fractions was 2 days with 67.5 J cm-2 fractions, and 3 days with 90 J cm-2 fractions. The time course of recovery of normal mouse tail skin from photodynamic therapy, as shown by these split dose experiments, was found to be similar to the time course for the recovery of blood flow following a single light treatment.

Strategies for selective cancer photochemotherapy: antibody-targeted and selective carcinoma cell photolysis

A principle objective in chemotherapy is the development of modalities capable of selectively destroying malignant cells while sparing normal tissues. One new approach to selective photochemotherapy, antibody-targeted photolysis (ATPL) uses photosensitizers (PS) coupled to monoclonal antibodies (MAbs) which bind to cell surface antigens on malignant cells. Selective destruction of human T leukemia cells (HBP-ALL) was accomplished by coupling the efficient PS chlorin e(6) to an anti-T cell MAb using dextran carriers. Conjugates with chlorin: MAb ratios of 30:1 retained > 85% MA b binding activity, and had a quantum yield for singlet oxygen production of 0.7 +/- 0.1, the same as that of free chlorin e(6). Cell killing was dependent on the doses of both MAb-PS and 630-670 nm light and occurred only in target cell populations which bound the MAb. On the order of 10(10) singlet oxygen molecules were necessary to kill a cell. A second approach to specific photochemotherapy, selective carcinoma cell photolysis (SCCP), relies on preferential accumulation of certain cationic PS by carcinoma cell mitochondria. We have evaluated several classes of cationic dyes, and in the case of N,N'-bis-(2-ethyl-1,3-dioxolane)-kryptocyanine (EDKC) and some of its analogs, have demonstrated highly selective killing of human squamous cell, bladder and colon carcinoma cells in vitro. In isolated mitochondria, EDKC uptake and fluorescence depended on membrane potential, and the dye specifically photosensitized damage to Complex I in the electron transport chain. N,N'-bis-(2-ethyl-1,3-dioxolane)-kryptocyanine and some of its analogs accumulated within subcutaneous xenografts of human tumors in nude mice with tumor:skin ratios > 8. Photoirradiation caused significant inhibition of tumor growth, without cutaneous phototoxicity.

Toxic and phototoxic effects of tetraphenylporphinesulphonate and haematoporphyrin derivative in vitro

The toxic and phototoxic effects of tetraphenylporphinesulphonate (TPPS4) and haematoporphyrin derivative (HpD) have been examined in vitro. TPPS4 was found to have less dark toxicity to the cells than HpD as measured by inhibition of cell multiplication and colony formation at comparable extracellular concentrations. TPPS4 was also less effective than was HpD in photoinactivating NHIK 3025 cells by more than a factor 2 which should be expected on the basis of cellular uptake. Spectrofluorometric data suggest that HpD in cells interacts more with lipids than TPPS4. This might explain the large photosensitizing effect of HpD compared to TPPS4 since the lifetime of singlet oxygen is about a factor of 10 longer in a lipid environment than in an aqueous environment. The uptake of TPPS4 and HpD by cancer cells in vitro does not correlate with previous in vivo data, indicating retention of TPPS4 in the tumour stroma. This makes in vitro/in vivo extrapolation difficult with regard to the use of TPPS4 as an agent for photodynamic therapy.

Antibody-targeted photolysis: selective photodestruction of human T-cell leukemia cells using monoclonal antibody-chlorin e6 conjugates

Selective in vitro photodestruction of HPB-ALL human T-cell leukemia cells was accomplished using the photosensitizer chlorin e6 coupled through dextran molecules to an anti-T-cell monoclonal antibody (mAb), anti-Leu-1. Conjugates with mAb/chlorin molar ratios as high as 1:36 retained mAb binding activity, and the absorption spectrum and quantum efficiency for singlet oxygen production of bound chlorin (0.7 +/- 0.2) were unchanged from that of the free photosensitizer. Phototoxicity, as measured by a clonogenic assay and by uptake of ethidium bromide, was dependent on the doses of both mAb-chlorin and 630- to 670-nm light, was enhanced by 2H2O, and was observed only in target populations that bound the mAb. Similarly, free chlorin e6 in solution had no photodynamic effect in amounts 100 times more than that carried by the mAb. For this antibody-targeted system, approximately 10(10) molecules of singlet oxygen were necessary to kill a cell.

Haematoporphyrin derivative photosensitization and gamma-radiation damage interaction in Chinese hamster ovary fibroblasts

The interaction of haematoporphyrin derivative (HPD) photosensitization and gamma-irradiation was studied with regard to clonogenicity of Chinese hamster ovary (CHO) fibroblasts. Exposure to either treatment alone resulted in shouldered response curves. Exposure to 4.2 Gy gamma-radiation immediately before graded doses of visible light had no effect on the shape of the visible-light survival curve; similarly, exposure to 8.75 kJ/m2 light immediately before graded doses of gamma-radiation had no effect on the shape of the gamma-radiation response curve. These data indicate that damage due to gamma-radiation and HPD photosensitization did not interact, suggesting that the mechanisms of cell killing are different.

Effect of bleaching of porphyrin sensitizers during photodynamic therapy

Cells of the line NHIK 3025 were incubated with the tumor-localizing porphyrin preparation DHE (Photofrin II). Exposure of light within the porphyrin absorption spectrum resulted in a change of the fluorescence spectra indicative of a movement of porphyrins from binding sites on proteins to more lipid environments, a degradation of the porphyrins in the cells without any significant formation of new porphyrin species. The photodegradation of the porphyrins resulted in a reduced yield of inactivation of cells per incident photon. Several independent estimations indicate that bleaching may play a role in clinical situations.

The cytotoxic activity of hematoporphyrin: studies on the possible role of transition metals

Hematoporphyrin acquires a potent cytolytic activity toward erythrocytes when activated by visible light. Considerable evidence has been obtained suggesting that this toxic activity is mediated by certain active oxygen species, including singlet oxygen and hydroxyl radicals. These active oxygen species have also been proposed as intermediates in the toxic activity of peroxidases, hemin, and a variety of metal complexes. Unlike hematoporphyrin, all these compounds contain a liganded Fe atom, which appears to play a central role in the activation of molecular oxygen. In order to ascertain whether the generation of active oxygen by hematoporphyrin may also involve the participation of a metal ion we have compared the cytolytic activity of hematoporphyrin with that of hematoheme. The participation of a metal ion in the light-activated hematoporphyrin reaction was ruled out on the basis of four criteria: no increase in cytolytic activity was observed upon the addition of Fe or Cu ions; no evidence could be obtained for the incorporation of a metal ion into hematoporphyrin during light activation; hematoporphyrin is a more potent cytolytic agent than hematoheme on an equimolar basis; and the activities of the two cytolytic agents are affected differently by various activators and inhibitors of the toxic reaction. Our results further indicate that the mechanism of the cytolytic activity promoted by light-activated hematoporphyrin is distinctly different from that promoted by hematoheme in the presence of ascorbate. We conclude that the two cytolytic reactions are most likely propagated by two different forms of active oxygen.

The interaction of hematoporphyrin derivative, light, and ionizing radiation in a rat glioma model

The effects of hematoporphyrin derivative, light, and cobalt 60 (60Co) irradiation were studied in a rat glioma model using an in vivo and an in vitro clonogenic assay. There was no effect on tumor growth by visible light or by a single dose of 60Co irradiation at 4 Gy or 8 Gy, whereas 16 Gy inhibited tumor growth to 40% versus the control. Hematoporphyrin derivative alone slightly stimulated growth (P less than 0.1). Light in the presence of 10 mg hematoporphyrin derivative/kg inhibited tumor growth to 32%. 60Co irradiation in the presence of hematoporphyrin derivative produced a significant tumor growth inhibition (P less than 0.02). This growth inhibition was directly related to the concentration of hematoporphyrin derivative. The addition of 60Co to light in the presence of hematoporphyrin derivative produced a greater growth inhibition than light or 60Co irradiation alone. This effect was most pronounced when light was applied 30 minutes before 60Co irradiation. Our experiments in a subcutaneous rat glioma model suggest a radiosensitizing effect of hematoporphyrin derivative. Furthermore, the photodynamic inactivation is enhanced by the addition of 60Co irradiation. These findings may be of importance in planning new treatment modalities in malignant brain tumors.

Cell uptake, distribution and response to aluminium chloro sulphonated phthalocyanine, a potential anti-tumour photosensitizer

The uptake, retention and effects of aluminium chloro sulphonated phthalocyanine (AlSPc) were measured in two cell lines, UV-2237 a murine fibrosarcoma and the non-tumorigenic NIH/3T3 fibroblast line. The behaviour of cells treated with AlSPc was compared with that of those treated with haematoporphyrin derivative (HpD), a photosensitizer often used in photodynamic therapy (PDT) of cancer. AlSPc absorbs light strongly in the red region, is taken up by cells in a dose dependent fashion and is retained in vitro over a period of days (5 days after exposure greater than 40% remains cell-associated versus less than 25% of HpD). Additionally AlSPc was less cytotoxic to cells, maintained in darkness or exposed to room light, compared to HpD (100% viability versus 0% viability 3 days after 60 min exposure to room light). However red light (approximately 600-700 nm) caused greater toxicity in AlSPc-treated cells (100%) than in similarly exposed HpD-treated cells (less than 60%). No significant differences were detected between the responses of the fibrosarcoma and the fibroblast cell lines. These characteristics of AlSPc suggest that it may prove to be a useful photosensitizer for PDT of cancer and this possibility is discussed.

Photodynamic therapy of prostate cancer: an in vitro study

The photo-induced toxicity of hematoporphyrin derivative on Dunning R3327 rat prostate cancer cells was studied. Dunning R3327 cells in culture were incubated for two hours in hematoporphyrin derivative and then exposed to red light at 630 nanometers wavelength from an argon pumped dye laser. Cell survival was measured for varying laser power densities, variable concentrations of hematoporphyrin derivative and variable light exposure times. AT1 cells not incubated with hematoporphyrin derivative were directly killed by laser light exposure at power densities greater than 500 mw./cm.2, probably due to hyperthermia. Cells that retained hematoporphyrin derivative were effectively killed using non-thermal levels of red light exposure due to a photochemical effect. Decreasing cell survival of cells that retained hematoporphyrin was related to increasing time of exposure to red light. This form of therapy may be applicable to the treatment of locally invasive prostatic carcinoma in man.

The binding of dihematoporphyrin ether (photofrin II) to human serum albumin

The variable aggregation of porphyrins such as Hp and Hpd introduces uncertainties and errors into attempts to measure their binding to proteins. Methods such as dialysis, ultrafiltration and gel chromatography, so frequently used, proved to be unreliable when applied to the binding of Hp to serum albumin. Quenching of tryptophan fluorescence will only occur at porphyrin binding sites which are closely situated to the tryptophan residue (1.7 nm). Porphyrin bound to more distant sites may not be included in this analytical procedure which must therefore be applied with reserve. In the present work, photofrin II (PII) was shown to consist of large aggregates greater than 20 000-30 000 Mr, solutions of which did not disaggregate on dilution down to 1 mumol/1. Addition of albumin resulted in a change in the absorption spectrum of PII. Thus, it was assumed that measurements of differential absorption gave the proportion of free-to-bound PII when serum albumin was added in graded amounts to its solution. By applying suitable calculations to the data, an association constant of 0.3 1/mumol +/- 30% was deducted. Hill plots of the binding data were linear with slopes close to unity. Experimentally determined uptake of PII by NHIK 3025 cells from solutions containing different amounts of HSA showed that the amount bound to the cells was proportional to the free PII. The kinetics of quenching of tryptophan fluorescence in HSA by PII indicates that there is one main porphyrin-binding site affecting this fluorescence. This binding site seems to have a slightly higher affinity for PII than the remaining sites. Up to 8 porphyrin rings of PII can be bound to an HSA molecule.

Phototoxic effects of hematoporphyrin derivative and its chromatographic fractions on hormone-producing human malignant trophoblast cells in vitro

The in vitro phototoxicity of HPD on malignant cells relative to normal cells has been examined. Two human malignant cell lines were studied: the BeWo line of choriocarcinoma cells, which secrete the tumor marker human chorionic gonadotropin (hCG) and its alpha-subunit; and the CaSki line of human cervical carcinoma cells, which secrete hCG and its beta-subunit. Trophoblast-derived, hCG-secreting cells from human amniotic fluid were used as normal controls. In all experiments with HPD plus light, a close correlation was found 24 h after light between cell number and RIA-detectable marker concentration in the medium. Phototoxicity was greater when HPD was introduced in serum-free rather than serum-containing medium. No toxicity was observed in light and dark controls. Cells in Leighton tubes were incubated 1 h with HPD (25 micrograms/ml) in serum-free medium, then rinsed and incubated with medium containing 10% serum. At 2 and 3 days after contact with HPD, flasks were exposed to cool white fluorescent light (1 mW/cm2) for 5 min. Viable cell counts taken 1 day after the light dose indicated that HPD is significantly more phototoxic to BeWo than to CaSki cells; and that both malignant cell types are more photosensitive than amniotic fluid cells, presumably because the latter retain HPD less effectively. In another aspect of this work BeWo cells were used as a model system for comparing the phototoxic effects of the fast (F) and slow (S) eluting fractions of HPD obtained by Bio-Gel P-10 chromatography. Cells in light-shielded tubes were sensitized by incubating with porphyrins for 20 h in media containing 10% calf serum. At 2, 3, or 4 days after removal of porphyrin, with daily replacement of serum-containing medium, flasks were irradiated (see above), and then incubated in the dark for 2 to 4 additional days. Daily culture fluids were analyzed for hormone levels (hCG alpha), and cell counts were performed 2 or 3 days after the light dose. HPD-S (25 micrograms/ml) had no effect on either hormone secretion or cell viability in any of the flasks, whether exposed to light or not. HPD-F at low concentrations (0.25 or 2.5 micrograms/ml) had no detectable effect on cell count or hormone secretion in irradiated flasks. At 10 micrograms/ml, HPD-F was innocuous in dark controls, but caused a large decrease in cell count and hormone output in irradiated flasks.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for a major role of plasma lipoproteins as hematoporphyrin carriers in vivo

Hematoporphyrin (5 mg/ml), administered intravenously to tumor-bearing patients, becomes associated with different serum proteins, including lipoproteins (mainly HDL), globulin and albumin. No residual porphyrin is bound to the two latter classes of proteins after 48 h, whereas the complexation with the lipoproteins appears to be particularly stable probably owing to the hydrophobic nature of hematoporphyrin. The late persistence of hematoporphyrin in serum is due to the binding to the VLDL fraction with special regard to its cholesterol moiety. The importance of hematoporphyrin transport by lipoproteins for the photodynamic therapy of tumors is briefly discussed.

Photodynamic therapy (PDT) of malignant tumors

Photodynamic therapy (PDT) is finding increasing application to a number of malignant tumors. It is based on the specific photosensitization of malignant tissue by a particular porphyrin derived from hematoporphyrin, known as Photofrin II. The exact structure at present is unknown. However this material, following systemic injection, is retained longer in malignant tissue than in many normal tissues and can be activated by visible light, usually red, to initiate a lethal phototoxic effect on the tumor. It is a particularly useful treatment when specificity is necessary in treatment, for example in treatment of widespread chest wall metastasis, bladder cancer and early lesions of the bronchus, trachea and esophagus, including CIS.

A preliminary comparison of the photosensitizing properties of porphyrins in aqueous solution and liposomal systems

The preliminary studies reported here show that at least some lipid soluble porphyrins can easily be incorporated into the membranes of liposomes prepared with different phospholipids; such porphyrins do not leach out of the membranes when the liposomes are stored in aqueous media. In this environment, the lipid soluble porphyrins are very effective photodynamic sensitizers for lipophilic substrates in the liposome membrane, for external amino acids and proteins, and for mammalian cells.

Time-resolved fluorescence microscopy of hematoporphyrin-derivative in cells

This work presents measurements of time-resolved fluorescence microscopy of hematoporphyrin-derivative (HpD) in single cells of mice tissue (both tumor and normal cells), in HeLa Cells, and in solution. The measurements were performed using a pulsed-laser microfluorometer with high spatial and temporal resolution. In agreement with the results obtained with other techniques, it has been found that the tumor cells examined present an HpD uptake about five times higher than that of the normal cells of the corresponding tissue and that, within a cell, HpD become localized mainly in the cytoplasm. It has also been found that the fluorescence decay time is different in cells as compared with solution, and that the presence of HpD stabilizes cell auto-fluorescence. These results are discussed.

Photodynamic effects of haematoporphyrin derivative on synchronized and asynchronous cells of different origin

Phototherapy in the presence of haematoporphyrin derivative has been shown to have a preferential effect on malignant tumours when compared to normal tissue. This communication presents a comparison of the sensitivity to photochemotherapy in vitro of different cell lines. Asynchronous populations of cells were exposed to light in the presence of haematoporphyrin derivative, and found to be inactivated with a comparable efficiency. The lines were of human, Chinese-hamster or mouse origin and had different abilities to form tumours after heterotransplantation into nude mice or transplantation into syngeneic, immunosuppressed mice. Synchronized cells from 4 of the lines showed a similar variation in sensitivity to light throughout the cell cycle. Cells near the middle of interphase showed the highest sensitivity, whilst cells in early G1 were found to be least sensitive towards treatment with haematoporphyrin derivative and light.

Multiplication of human NHIK 3025 cells exposed to porphyrins in combination with light

Cells from the established line NHIK 3025 were exposed to haematoporphyrin derivative and light. After this photodynamic treatment the first interphase of surviving cells was prolonged. Furthermore, a pronounced effect on the progression through the first mitosis was observed. Mainly the duration of metaphase was increased. Some of the cells were irreversibly arrested in mitosis and the cells that were able to complete mitosis after treatment multiplied in the subsequent generations at the same rate as the control. Cells treated in the late stages of the mitosis went out of mitosis at the same rate as the control. This indicates that the treatment with porphyrins and light induces a block in a specific stage of mitosis.