Singlet oxygen generation of porphyrins, chlorins, and phthalocyanines

Oxygen depletion during in vitro photodynamic therapy: structure-activity relationships of sulfonated aluminum phthalocyanines

Photodynamically induced oxygen depletion has been measured in an Ehrlich ascites mouse tumor cell line using a Clark-type electrode. Cells are loaded with aluminum phthalocyanines, sulfonated to different degrees (A1PcS(n), n = 0,2,3,4) and consisting of various isomeric species. Different cell lines and incubation procedures are used in order to investigate the cellular uptake mechanism. Uptake (in units of molecules/cell), post-irradiation redistribution and A1PcS(n) photodegradation are measured using spectroscopic techniques. For a given sensitizer, the oxygen depletion rate per cell increases sublinearly with uptake and superlinearly with cell density. In order to compare oxygen depletion rates of different compounds, we have defined the biological quantum yield (BQY) as the number of oxygen molecules that disappear per absorbed photon. The BQY is independent of uptake and cell density; therefore, it denotes the intrinsic photoactivity of a sensitizer. Sensitizers with high BQY show efficient post-irradiation intracellular redistribution. Photodegradation during irradiation is similar for all sensitizers (20-30%).

BPD-MA-mediated photosensitization in vitro and in vivo: cellular adhesion and beta1 integrin expression in ovarian cancer cells

Benzoporphyrin derivative monoacid (BPD-MA) photosensitization was examined for its effects on cellular adhesion of a human ovarian cancer cell line, OVCAR 3, to extracellular matrix (ECM) components. Mild BPD-MA photosensitization (approximately 85% cell survival) of OVCAR 3 transiently decreased adhesion to collagen IV, fibronectin, laminin and vitronectin to a greater extent than could be attributed to cell death. The loss in adhesiveness was accompanied by a loss of beta1 integrin-containing focal adhesion plaques (FAPs), although beta1 subunits were still recognized by monoclonal antibody directed against human beta1 subunits. In vivo BPD-MA photosensitization decreased OVCAR 3 adhesiveness as well. Photosensitized adhesion was reduced in the presence of sodium azide and enhanced in deuterium oxide, suggesting mediation by singlet oxygen. Co-localization studies of BPD-MA and Rhodamine 123 showed that the photosensitizer was largely mitochondrial, but also exhibited extramitochondrial, intracellullar, diffuse cytosolic fluorescence. Taken together, these data show that intracellular damage mediated by BPD-PDT remote from the FAP site can affect cellular-ECM interactions and result in loss of FAP formation. This may have an impact on long-term effects of photodynamic therapy. The topic merits further investigation.

Oxygen diffusion and reaction kinetics in the photodynamic therapy of multicell tumour spheroids

Effects of oxygen diffusion and reaction kinetics in photodynamic therapy are considered in the context of a multicell tumour spheroid model. Steady-state measurements of oxygen made with a Clark-style microelectrode (4 microm diameter tip) enable us to determine the rate of metabolic oxygen consumption and the oxygen diffusion coefficient in 500 microm diameter EMT6/Ro spheroids. These values are 5.77 micromol 1(-1) s(-1) and 1460 microm2 s(-1), respectively. Time-dependent electrode measurements of oxygen concentration during laser irradiation of individual Photofrin-sensitized spheroids are fitted to numerical solutions of a pair of diffusion-with-reaction equations. The analysis yields the rate of photodynamic oxygen consumption and a parameter that governs the oxygen sensitivity of photodynamic therapy. These experimentally derived quantities are used to calculate the temporal and spatial distributions of oxygen and the rate of oxygen consumption in a spheroid during irradiation at several fluence rates. The spatial distribution of photodynamic oxygen consumption is strongly fluence rate dependent. Using the experimental and theoretical results developed in this report, previously published survival data are analysed. The analysis indicates that the threshold dose of reacting singlet oxygen in the EMT6/Ro spheroid is 323 +/- 38 micromol 1(-1) (mean +/- SEM).

Correlation of subcellular and intratumoral photosensitizer localization with ultrastructural features after photodynamic therapy

Photodynamic therapy (PDT) of cancer typically involves systemic administration of tumor-localizing photosensitizers followed 48-72 h later by exposure to light of appropriate wavelengths. Knowledge about the distribution of photosensitizers in tissues is still fragmentary. In particular, little is known as to the detailed localization patterns of photosensitizers in neoplastic and normal tissues as well as the relationship between such patterns and the actual targets for the photosensitizing effect. This review focuses on ultrastructural features seen in treated cells and tumors. An attempt is made to correlate these findings with the subcellular/intratumoral localization pattern of the photosensitizers in tumor cell lines in vitro and in tumor models in vivo. Several subcellular sites are main targets of PDT with different sulfonated aluminum phthalocyanines (AIPcSn) in the human tumor cell line LOX. Nuclei are not among the primary targets. Overall, the ultrastructural changes correlate well with the data about the subcellular localization patterns for each analogue of AIPcSn in the same cell line. Similar findings are also obtained for the family of sulfonated mesotetraphenylporphines (TPPSn) in the NHIK 3025 cell line. The mechanisms involved in the killing of tumors by PDT seem to be a complex interplay between direct and indirect (via vascular damage) effects on neoplastic cells according to the intratumoral localization pattern of the applied dye. Several factors can affect the localization pattern of a drug, such as its chemical character, the mode of drug delivery, the time interval between drug administration and light exposure, and tumor type. Furthermore, whether local immune reactions (such as macrophages) and apoptosis (programmed cell death) are involved in the destruction of neoplastic cells by PDT in vivo is still an enigma. A general model for PDT-induced tumor destruction is suggested.

Photosensitization of the rat endometrium following 5-aminolevulinic acid induced photodynamic therapy

BACKGROUND AND OBJECTIVE

The impact of photodynamic therapy (PDT) on the endometrium following topical application of 5-aminolevulinic acid (ALA) was studied in a rat model. Study Design/

MATERIALS AND METHODS

Fluorescence microscopy revealed peak ALA to protoporphyrin IX (Pp IX) conversion 3-6 hours after application. Significantly higher Pp IX levels were observed in the endometrial glands compared with endometrial stroma and myometrium.

RESULTS

Histological studies showed PDT-induced endometrial destruction with atrophy 7-10 weeks after treatment. Reproductive performance studies demonstrated significant implantation failure in the treated uterine horns compared with controls. The number of implantation sacs in the treated and untreated horns was 0.4 +/- 0.3 and 8.9 +/- 1.0, respectively (P < 0.01).

CONCLUSION

We conclude that the high rate of Pp IX conversion in the endometrial glands can be exploited to treat dysfunctional uterine bleeding with PDT. In addition, this concept may also be applied to study endometrial regeneration and embryo implantation mechanisms.

Correlation of distribution of sulphonated aluminium phthalocyanines with their photodynamic effect in tumour and skin of mice bearing CaD2 mammary carcinoma

A chemical extraction assay and fluorescence microscopy incorporating a light-sensitive thermoelectrically cooled charge-coupled device (CCD) camera was used to study the kinetics of uptake, retention and localisation of disulphonated aluminium phthalocyanine (A1PcS2) and tetrasulphonated aluminium phthalocyanine (A1PcS4) at different time intervals after an i.p. injection at a dose of 10 mg kg-1 body weight (b.w.) in tumour and surrounding normal skin and muscle of female C3D2/F1 mice bearing CaD2 mammary carcinoma. Moreover, the photodynamic effect on the tumour and normal skin using sulphonated aluminium phthalocyanines (A1PcS1, A1PcS2, A1pcS4) and Photofrin was compared with respect to dye, dye dose and time interval between dye administration and light exposure. The maximal concentrations of A1PcS2 in the tumour tissue were reached 2-24 h after injection of the dye, while the amounts of A1PcS4 peaked 1-2 h after the dye administration. A1PcS2 was simultaneously localised in the interstitium and in the neoplastic cells of the tumour, whereas A1PcS4 appeared to localise only in the stroma of the tumour. The photodynamic efficiency (light was applied 24 h after dye injection at a dose of 10 mg kg-1 b.w.) of the tumours was found to decrease in the following order: A1PcS2 > A1PcS4 > Photofrin > A1PcS1. Furthermore, photodynamic efficacy was strongly dependent upon dye doses and time intervals between dye administration and light exposure: the higher the dose, the higher the photodynamic efficiency. The most efficient photodynamic therapy (PDT) of the tumour was reached (day 20 tumour-free) when light exposure took place 2 h after injection of A1PcS2 (10 mg kg-1). A dual intratumoral localisation pattern of the dye, as found for A1PcS2, seems desirable to obtain a high photodynamic efficiency. The kinetic patterns of uptake, retention and localisation of A1PcS2 and A1PcS4 are roughly correlated with their photodynamic effect on the tumour and normal skin.

Role of oxygen in the phototoxicity of phthalocyanines

The presence of molecular oxygen is a determinant in the phototoxicity of phthalocyanines, and photosensitized oxidation is the accepted chemical mechanism for photo-dynamic action. However, it is difficult to establish whether the process is initiated by a type I electron transfer, or by a type II energy transfer reaction to form singlet oxygen. Usually, the involvement of singlet oxygen in photodamage has been indicated by the inhibition of the biological effect by a competitive physical or chemical singlet oxygen quencher, or by a rate increase in D2O, in which singlet oxygen has a longer lifetime than in H2O. Unfortunately, these techniques are not completely specific for singlet oxygen. Moreover, thermodynamic considerations suggest that photoinduced electron abstraction from appropriate biomaterials could compete with singlet oxygen production under in vivo conditions. This likely source of one electron-oxidized primary radicals, which can provide the precursors of the oxidative damage in phthalocyanine photosensitization, suggests the possibility of modulated toxicity by interaction with chemical additives. Examples of such additives recently studied are ascorbate, tocopherol and quercetin, all of which are natural antioxidants.

Singlet oxygen generation by Photofrin in homogeneous and light-scattering media

The singlet oxygen quantum yield (phi delta) for Photofrin solubilized by Triton X-100 was measured in homogeneous and light-scattering media using the photosensitized inactivation of lysozyme as an internal actinometer. Higher values of phi delta at 630 nm than at 514 nm are attributed to the formation of a far-red-absorbing photosensitizing photoproduct.

Photodynamic destruction of endometrial tissue with topical 5-aminolevulinic acid in rats and rabbits

OBJECTIVE

The goal of this study was to determine the optimal parameters for photodynamic endometrial destruction with topically applied 5-aminolevulinic acid, a precursor for the endogenous synthesis of the fluorescent photosensitizer protoporphyrin IX.

STUDY DESIGN

5-Aminolevulinic acid pharmacokinetics were measured in rat and rabbit models by analyzing tissue frozen sections 3 to 12 hours after topical administration. Dose-response studies were conducted for 100 to 400 mg/ml 5-aminolevulinic acid. Photodynamic therapy was performed intraluminally, and tissue morphologic features were evaluated 3 and 7 days after treatment.

RESULTS

Peak fluorescence was observed 3 hours after topical administration. Glandular fluorescence significantly exceeded stromal and myometrial in all studies, particularly for 200 mg/ml 5-aminolevulinic acid. Histologic studies revealed persistent epithelial destruction with minimal regeneration.

CONCLUSION

Topical 5-aminolevulinic acid photodynamic therapy can be used for highly effective, long-lasting destruction of endometrial epithelium. However, optical dosimetry can vary, particularly in the rabbit model, and this appears to have an impact on long-term reepithelialization.

Potential photosensitizers for photodynamic therapy. IV. Photophysical and photochemical properties of azaporphyrin and azachlorin derivatives

The photophysical and photochemical properties of a 5-azaprotoporphyrin derivative ([5]AZPP), a zinc-15-azaporphyrin derivative (Zn-[15]AZIDP) and an E-Z isomeric mixture of a 5-azachlorin derivative ([5]AZCH) were studied in various solvents. The quantum yields of fluorescence phi F0, S1-T1 intersystem crossing phi T0 and singlet oxygen (1 delta g) formation phi delta were measured and the Stern-Volmer constants for the quenching of the S1 states by oxygen and the rate constants of quenching of O2(1 delta g) by the different azaporphyrinoid compounds were obtained. The fluorescence quantum yield (phi F0 = 0.23), the strong absorption in the red (lambda max = 674 nm, epsilon max = 66,000 M-1 cm-1) and the high value of the quantum yield for singlet oxygen (1 delta g) formation (phi delta = 0.65) observed for [5]AZCH recommend azachlorin derivatives as potential markers and photosensitizers for tumour therapy.

Laser-induced fluorescence in malignant and normal tissue of rats injected with benzoporphyrin derivative

Laser-induced fluorescence was used to characterize the localization of intravenously administered benzoporphyrin derivative-monoacid (BPD-MA) 3 h postinjection in different rat tissue types, including an induced experimental malignant tumor. A comparison of the fluorescence properties and demarcation potential between the newer sensitizer BPD-MA and four other substances, hematoporphyrin (HP), polyhematoporphyrin ester (PHE), tetrasulfonated phthalocyanine (TSPc) and the commercially available Photofrin earlier investigated, is included. The fluorescence light was induced with a nitrogen laser, emitting at 337 nm. The fluorescence spectrum in the region 380-750 nm was analyzed by a polychromator equipped with a diode array detector. The demarcation potential between tumor and surrounding tissue in terms of fluorescence signal for the tumor model used was 2:1 for BPD-MA. In comparison with the other drugs, HP shows about the same demarcation potential, whereas Photofrin and PHE exhibit about 3 times better and TSPc about 1.5 times better demarcation. By also employing the endogenous tissue fluorescence signature the contrast was enhanced by a factor of about 2 for each of the five drugs.

Normal brain tissue response to photodynamic therapy using aluminum phthalocyanine tetrasulfonate in the rat

The effects of photodynamic therapy (PDT) on normal brain tissue and depth of brain necrosis were evaluated in rats receiving 2.5 mg/kg aluminum phthalocyanine tetrasulfonate. Twenty-four hours later brains were irradiated with 675 nm light at a power density of 50 mW/cm2 and energy doses ranging from 1.6 to 121.5 J/cm2. Brains were removed 24 h after PDT and evaluated microscopically. When present, brain lesions consisted of well-demarcated areas of coagulation necrosis. When plotting the depth of necrosis against the natural log of energy dose, the data fit a piecewise linear model, with a changepoint at 54.6 J/cm2 and an x intercept of 7.85 J/cm2. The slopes before and after the changepoint were 2.04 and 0.21 mm/ln J cm-2, respectively. The x intercept suggests a minimum light dose below which necrosis of normal brain will not occur, whereas the changepoint indicates the energy density corresponding to an approximate maximum depth of necrosis.

Effect of administration route and estrogen manipulation on endometrial uptake of Photofrin porfimer sodium

OBJECTIVE

Our purpose was to evaluate the influence of the route of drug administration and target tissue vascularity on the distribution of a photosensitizer, Photofrin porfimer sodium, in the uterus.

STUDY DESIGN

The study was divided in two phases. In phase I 80 mature female rats were hormonally suppressed and then stimulated with estrogen. They were randomized to receive intravenous, intraperitoneal, or intrauterine Photofrin and killed 3, 6, 24, or 48 hours later. Drug distribution and levels were then determined. In phase II 40 female rats were randomized to receive hormonal stimulation, suppression, both, or neither. All received intrauterine Photofrin and were killed 24 hours later. Statistical analysis was performed with the unpaired t test and the two-way analysis of variance.

RESULTS

Intrauterine administration was determined to be the simplest and most effective method of delivery because it provided for optimal uptake and distribution (p = 0.05) within the uterus, at lower doses.

CONCLUSIONS

Selective localization of photosensitizer within the target tissue suggests that highly selective photodynamic destruction of endometrial tissue can be achieved. Furthermore, the combination of intrauterine administration of photosensitizer with estrogen adjuvant may minimize the most debilitating side effect of Photofrin, cutaneous phototoxicity.

Photosensitizing properties of mono-L-aspartyl chlorin e6 (NPe6): a candidate sensitizer for the photodynamic therapy of tumors

There is a large amount of interest in chlorins as photosensitizers for the photodynamic therapy of tumors because of their strong absorption in the red, where light penetration into mammalian tissues is efficient. Mono-L-aspartyl chlorin e6 (NPe6), in phosphate buffer of pH 7.4, had absorption peaks at 400 and 654 nm with molar absorption coefficients of 180,000 and 40,000 M-1 cm-1 respectively. In buffer, the NPe6 triplet had a peak at 440 nm and a lifetime under argon of approximately 300 microseconds. The triplet was efficiently quenched by ground state oxygen (kQ = 1.9 x 10(9) M-1 s-1) with the formation of singlet oxygen, as identified by its near infrared luminescence. The quantum yield of singlet oxygen production was 0.77. A number of substrates were efficiently photo-oxidized by NPe6, including furfuryl alcohol, cysteine, histidine, tryptophan and human serum albumin. These reactions were efficiently inhibited by azide (which did not quench NPe6 triplets), indicating that they are probably mediated by singlet oxygen. Thus, NPe6 has a desirable array of photoproperties for a sensitizer to be used in the clinical photodynamic therapy of tumors.

Photobleaching of 1,3-diphenylisobenzofuran by novel phthalocyanine dye derivatives

As part of a wider programme to identify novel photosensitizers for photodynamic therapy, the ability of a number of phthalocyanine dyes, including some novel copper phthalocyanine derivatives with a range of water solubilities, to produce potentially cytotoxic species in solution was examined. The experiments were performed in dimethylformamide using 1,3-diphenylisobenzofuran (DPIBF) as the scavenger. The study revealed that all the dyes tested produced DPIBF photobleaching on illumination in vitro, but with widely different (greater than 12x) rates. The possible correlation of DPIBF photobleaching rates with a number of the dyes' properties is discussed.

Quantum yields and kinetics of the photobleaching of hematoporphyrin, Photofrin II, tetra(4-sulfonatophenyl)-porphine and uroporphyrin

Porphyrins used as sensitizers for the photodynamic therapy (PDT) of tumors are progressively destroyed (photobleached) during illumination. If the porphyrin bleaches too rapidly, tumor destruction will not be complete. However, with appropriate sensitizer dosages and bleaching rates, irreversible photodynamic injury to the normal tissues surrounding the tumor, which retain less sensitizer, may be significantly decreased. This paper surveys the quantum yields and kinetics of the photobleaching of four porphyrins: hematoporphyrin (HP), Photofrin II (PF II), tetra(4-sulfonatophenyl)porphine (TSPP) and uroporphyrin I (URO). The initial quantum yields of photobleaching, as measured in pH 7.4 phosphate buffer in air, were: 4.7 x 10(-5), 5.4 x 10(-5), 9.8 x 10(-6), and 2.8 x 10(-5) for HP, PF II, TSPP and URO respectively; thus, the rates of photobleaching are rather slow. Low oxygen concentration (2 microM) significantly reduced the photobleaching yields. However, D2O increased the yields only slightly, and the singlet oxygen quencher, azide, had no effect, even at 0.1 M. Photosensitizing porphyrins in body fluids, cells and tissues may be closely associated with various photooxidizable molecules and electron acceptors and donors. Therefore, selected model compounds in these categories were examined for their effects on porphyrin photobleaching. A number inhibited and/or accelerated photobleaching, depending on the compound, the porphyrin and the reaction conditions. For example, 1.0 mM furfuryl alcohol increased the photobleaching yields of HP and URO more than 5-fold, with little effect on PF II or TSPP. In contrast, the electron acceptor, methyl viologen, increased the photobleaching yield of TSPP more than 10-fold, with little accelerating effect on the other porphyrins. These results suggest that the mechanism(s) of the photobleaching of porphyrin photosensitizers in cells and tissues during PDT may be complex.

Use of photosensitive, antibody directed liposomes to destroy target populations of cells in bone marrow: a potential purging method for autologous bone marrow transplantation

Liposomes containing the photosensitive dye sulphonated aluminium phthalocyanine (AlSPc) were coupled to polyclonal sheep anti-mouse-Ig antibody and bound to cells coated with specific mouse monoclonal antibody. When illuminated with red light, the AlSPc in the liposomes was activated to produce singlet oxygen and the antibody and liposome targeted cells were destroyed. DW-BCL cells (an Epstein Barr virus immortalised B-cell line) were targeted with an anti-B-cell antibody (8A) and killed specifically, both alone and in the presence of bone marrow mononuclear cells (BM-cells), without phototoxic effects on the untargeted bone marrow CFU-GM progenitor cells. The presence of an excess of non-target cells did not interfere with antibody and liposome binding, or light access to target cells. Similar results were obtained with T-lymphocytes as target cells using anti-CD3 antibody. Specific targeting to the B-cells was demonstrated in the cell mixtures by use of fluorescent microscopy combined with a sensitive technique to detect low levels of AlSPc fluorescence, a cooled charge couple device (CCD) camera. This was also able to show low levels of non-specific background binding of AlSPc to BM-cells and a small population of cells that took up AlSPc in the absence of antibody. The latter were shown to be monocytes by flow cytometry.

Photofrin II photosensitization is mutagenic at the tk locus in mouse L5178Y cells

Photosensitization mediated by Photofrin II (PFII) was found to be mutagenic at the heterozygous thymidine kinase (tk) locus in mouse L5178Y lymphoma strains LY-S1 and LY-R16 but not in strain LY-R83 which is hemizygous at the tk locus. After treatments yielding 37% survival, the mutagenicity of photosensitization with PFII in strain LY-S1 was similar to that of other mutagenic agents including x-radiation, ethyl methanesulfonate, and photosensitization with chloroaluminum phthalocyanine (AlPcCl). Although both strain LY-S1 and strain LY-R16 were mutagenized by photosensitization with PFII, only strain LY-S1 was mutagenized by photosensitization with AlPcCl. The non-mutability of strain LY-R83 following photodynamic treatment with either sensitizer may be because of the poor recovery of mutants with intergenic mutations in this TK+/0 hemizygous strain, whereas the non-mutability of strain LY-R16 subjected to photodynamic treatment with AlPcCl may be because LY-R16 cells sustaining mutagenic damage do not survive for reasons other than the loss of an essential gene.

Photo-immunotargeting with haematoporphyrin conjugates activated by a low-power He-Ne laser

A combined method has been developed for selective cytolysis in vitro as well as in vivo using a photosensitizer haematoporphyrin-protein conjugate as the targeting molecule and low-power He-Ne laser (632.8 nm) irradiation in order to activate the sensitizer to its excited, toxic triplet energy state. The specificity of the procedure was demonstrated in vitro by purging a mixed cell population from one component, and in vivo in an animal (nude mice) xenograft tumour model, where human cancer cells were destroyed by the immunotargeting method using monoclonal-antibody-haematoporphyrin (mAb-HP) conjugate (a-PNAr-I mAbs, which bind to the cell surface antigens of gastric cancer cells) and soft laser irradiation. The cell destruction was dependent on the doses of both mAb-HP and He-Ne laser light energy, and occurred only in target cell populations.

In vivo tumor oxygen tension measurements for the evaluation of the efficiency of photodynamic therapy

Among the sequence of events which occur during photodynamic therapy (PDT) are depletion of oxygen and disruption of tumor blood flow. In order to more clearly understand these phenomena we have utilized transcutaneous oxygen electrodes to monitor tissue oxygen disappearance. These results provide, for the first time, non-invasive real-time information regarding the influence of light dose on tissue oxygenation during irradiation. Measurements were conducted on transplanted VX-2 skin carcinomas grown in the ears of New Zealand white rabbits. Rabbits were treated with Photofrin II and tumors were irradiated with up to 200 kJ/m2 (500 W/m2) of 630-nm light. Substantial reductions in tumor oxygen tension were observed upon administration of as little as 20 kJ/m2. For a series of brief irradiations, oxygen tension was modulated by the appearance of laser light. Tissue oxygen reversibility appeared to be dependent upon PDT dose. Long-term, irreversible tissue hypoxia was recorded in tumors for large (200 kJ/m2) fluences. These results suggest that transcutaneous oxygen tension may be useful as a general indicator of the effectiveness of PDT and as an in situ predictor of the energy required to elicit tumor damage.

Chlorins as photosensitizers in biology and medicine

The photodynamic therapy (PDT) of tumors involves illumination of the tumorous area following the administration of a tumor-localizing photodynamic sensitizer. Hematoporphyrin derivative (HPD) and Photofrin II (a purified form of HPD), the main sensitizers used clinically for PDT to date, are complex mixtures of porphyrins; furthermore, these preparations absorb light very poorly in the red region of the spectrum (wavelengths greater than 600 nm) where light penetration into mammalian tissues is greatest. Thus there is considerable interest in identifying new sensitizers that localize more effectively in tumors, absorb more strongly at longer wavelengths and can be prepared in high purity. Much of this interest has been directed towards chlorins (reduced porphyrins), which typically absorb strongly in the red. This review summarizes research that has been carried out on selected types of chlorins, some of which may have important applications as sensitizers for PDT.