Evidence against the production of superoxide by photoirradiation of hematoporphyrin derivative

Oxygen removal during pathogen inactivation with riboflavin and UV light preserves protein function in plasma for transfusion

BACKGROUND AND OBJECTIVE

Photochemical pathogen inactivation technologies (PCT) for individual transfusion products act by inhibition of replication through irreversibly damaging nucleic acids. Concern on the collateral impact of PCT on the blood component's integrity has caused reluctance to introduce this technology in routine practice. This work aims to uncover the mechanism of damage to plasma constituents by riboflavin pathogen reduction technology (RF-PRT).

METHODS

Activity and antigen of plasma components were determined following RF-PRT in the presence or absence of dissolved molecular oxygen.

RESULTS

Employing ADAMTS13 as a sentinel molecule in plasma, our data show that its activity and antigen are reduced by 23 ± 8% and 29 ± 9% (n = 24), respectively, which corroborates with a mean decrease of 25% observed for other coagulation factors. Western blotting of ADAMTS13 shows decreased molecular integrity, with no obvious indication of additional proteolysis nor is riboflavin able to directly inhibit the enzyme. However, physical removal of dissolved oxygen prior to RF-PRT protects ADAMTS13 as well as FVIII and fibrinogen from damage, indicating a direct role for reactive oxygen species. Redox dye measurements indicate that superoxide anions are specifically generated during RF-PRT. Protein carbonyl content as a marker of disseminated irreversible biomolecular damage was significantly increased (3·1 ± 0·8 vs. 1·6 ± 0·5 nmol/mg protein) following RF-PRT, but not in the absence of dissolved molecular oxygen (1·8 ± 0·4 nmol/mg).

CONCLUSIONS

RF-PRT of single plasma units generates reactive oxygen species that adversely affect biomolecular integrity of relevant plasma constituents, a side-effect, which can be bypassed by applying hypoxic conditions during the pathogen inactivation process.

Is delta-aminolevulinic acid dehydratase rate limiting in heme biosynthesis following exposure of cells to delta-aminolevulinic acid?

Understanding the regulation and control of heme/porphyrin biosynthesis is critical for the optimization of the delta-aminolevulinic-acid (ALA)-mediated photodynamic therapy of cancer, in which endogenously produced protoporphyrin IX (PPIX) is the photosensitizer. The human breast cancer cell line MCF-7, the rat mammary adenocarcinoma cell line R3230AC, the mouse mammary tumor cell line EMT-6 and the human mesothelioma cell line H-MESO-1 were used to study ALA-induced PPIX levels and their relationship to delta-aminolevulinic acid dehydratase (ALA-D) activity in vitro. Incubation of these cell lines with 0.5 mM ALA for 3 h resulted in a significant increase in PPIX accumulation, compared with control cells, but there was no significant change in ALA-D activity. Exposure of cells incubated with ALA to 30 mJ/cm2 of fluorescent light, a dose that would cause a 50% reduction in cell proliferation, did not significantly alter the activity of ALA-D. Increasing the activity of porphobilinogen deaminase (PBGD), the enzyme immediately subsequent to ALA-D, by four- to seven-fold via transfection of cells with PBGD complementary DNA did not alter the activity of ALA-D. However, incubation of cells with various concentrations of succinyl acetone, a potent inhibitor of ALA-D, caused a concomitant decline in both PPIX accumulation and ALA-D activity. These data imply that when cells are exposed to exogenous ALA, ALA-D is an important early-control step in heme/porphyrin biosynthesis and that regulation of PPIX synthesis by this dehydratase may impact the effectiveness of ALA-mediated photosensitization.

Anti-angiogenic activity of selected receptor tyrosine kinase inhibitors, PD166285 and PD173074: implications for combination treatment with photodynamic therapy

Angiogenesis, the formation of new blood vessels from an existing vasculature, is requisite for tumor growth. It entails intercellular coordination of endothelial and tumor cells through angiogenic growth factor signaling. Interruption of these events has implications in the suppression of tumor growth. PD166285, a broad-spectrum receptor tyrosine kinase (RTK) inhibitor, and PD173074, a selective FGFR1TK inhibitor, were evaluated for their anti-angiogenic activity and anti-tumor efficacy in combination with photodynamic therapy (PDT). To evaluate the anti-angiogenic and anti-tumor activities of these compounds, RTK assays, in vitro tumor cell growth and microcapillary formation assays, in vivo murine angiogenesis and anti-tumor efficacy studies utilizing RTK inhibitors in combination with photodynamic therapy were performed. PD166285 inhibited PDGFR-beta-, EGFR-, and FGFR1TKs and c-src TK by 50% (IC50) at concentrations between 7-85 nM. PD173074 displayed selective inhibitory activity towards FGFR1TK at 26 nM. PD173074 demonstrated (>100 fold) selective growth inhibitory action towards human umbilical vein endothelial cells compared with a panel of tumor cell lines. Both PD166285 and PD173074 (at 10 nM) inhibited the formation of microcapillaries on Matrigel-coated plastic. In vivo anti-angiogenesis studies in mice revealed that oral administration (p.o.) of either PD166285 (1-25 mg/kg) or PD173074 (25-100 mg/kg) generated dose dependent inhibition of angiogenesis. Against a murine mammary 16c tumor, significantly prolonged tumor regressions were achieved with daily p.o. doses of PD166285 (5-10 mg/kg) or PD173074 (30-60 mg/kg) following PDT compared with PDT alone (p<0.001). Many long-term survivors were also noted in combination treatment groups. PD166285 and PD173074 displayed potent anti-angiogenic and anti-tumor activity and prolonged the duration of anti-tumor response to PDT. Interference in membrane signal transduction by inhibitors of specific RTKs (e.g. FGFR1TK) should result in new chemotherapeutic agents having the ability to limit tumor angiogenesis and regrowth following cytoreductive treatments such as PDT.

Uptake and kinetics of 14C-labelled meta-tetrahydroxyphenylchlorin and 5-aminolaevulinic acid in the C6 rat glioma model

Meta-tetrahydroxyphenylchlorin (m-THPC) and 5-aminolaevulinic acid (5-ALA) are two second-generation photosensitizers which are currently under investigation for photodynamic therapy (PDT) and photodynamic diagnosis (PDD). So far, the experience with these photosensitizers for use within brain tumours is limited. We examined the distribution and retention of 14C-labelled m-THPC and [14C]5-ALA in the rat C6 glioma brain tumour model. After intraperitoneal injection of m-THPC (71,909 d.p.m. microl(-1); 0.16 mg ml(-1) m-THPC; 0.3 mg kg(-1)), the following activities were found after 36 h: brain tumour 223,664 d.p.m. g(-1), brain contralateral to the tumour side 2567 d.p.m. g(-1), liver 369,959 d.p.m. g(-1) and skin 55,197 d.p.m. g(-1); 100,000 d.p.m. corresponding to 0.22 microg of m-THPC. After 7 days, the concentration of m-THPC decreased to 76,277 d.p.m. g(-1) in tumour and 635 d.p.m. g(-1) in brain. The radioactivity after intravenous administration of [14C]5-ALA (23,079 d.p.m. microl(-1); 40 mg ml(-1); 120 mg kg(-1)) increased within 15 min (59,634 d.p.m. g(-1) in tumour, 17,427 d.p.m. g(-1) in brain); after 8 h only a small amount (3653 d.p.m. g(-1) in tumour) remained. Brain adjacent to the tumour was also found to have a higher uptake of 5-ALA. This study provides basic information for the use of m-THPC and 5-ALA in brain tumours. Because of the different pharmacokinetic and toxicological profile, we recommend m-THPC for PDT and 5-ALA for PDD. Clinical trials now have to prove the superior phototoxic properties of these second-generation photosensitizers.

The importance of liposomes as models and tools in the understanding of photosensitization mechanisms

The various applications of liposomes in understanding photosensitization are described in this paper, with particular emphasis on the various kinds of information that these models allow to obtain in phototherapy. Liposomes are simple vesicles in which an aqueous phase is enclosed by a phospholipidic membrane. They are suitable models mimicking specific situations occurring in vivo and they allow study of the influence of physicochemical, photobiological and biochemical factors on the uptake of photosensitizers by tissues, their mechanisms of action and the subsequent photoinduced tumor necrosis. Moreover, solubilization of the sensitizer into the bilayer seems to improve its tumoral selectivity and its photodynamic efficiency.

Efficacy of photodynamic therapy on original and recurrent rat mammary tumors

Photodynamic therapy has demonstrated efficacy toward primary, metastatic and recurrent human tumors. Here, we investigated the ability of photodynamic therapy, using Photofrin, to inhibit growth of R3230AC mammary adenocarcinomas when tumors were treated as original implants and again as lesions recurring at the initial treatment site. The results demonstrate that both initial implants and lesions recurring after the first photodynamic treatment respond similarly to the same photodynamic therapy protocol, with mean tumor volume doubling times of approximately 11 days in both cases. Cells cultured from original tumor implants or tumors that recurred after photodynamic treatment accumulate equivalent amounts of [14C]polyhematoporphyrin. Single cell suspensions prepared from either original or recurrent tumors from animals administered 5 mg/kg Photofrin and exposed to light in vitro displayed comparable phototoxicity. Additionally, examination of tumors by light microscopy revealed no morphological differences between the original tumor implants and the recurrent lesions. Taken together, these data indicate that lesions which recurred at the site of the initial photodynamic treatment were not resistant to a second identical course of photodynamic therapy.

Effects of photodynamic therapy on xenografts of human mesothelioma and rat mammary carcinoma in nude mice

We have examined the effectiveness of photodynamic therapy against R3230AC rat mammary adenocarcinoma and human mesothelioma as xenografts in the same host. The results demonstrate that the xenografted human tumour is significantly more responsive to photodynamic treatment than the rodent mammary tumour. Studies also showed that the mesothelioma xenograft was fluence rate- and fluence-dependent while the rat tumour exposed to the same conditions demonstrated neither of these dependencies. This disparity in response was not attributable to a difference in either whole-tumour uptake or subcellular distribution of the porphyrin photosensitiser. Analysis of the effects of visible irradiation on cytochrome c oxidase activity, measured in mitochondria prepared from tumours borne on hosts injected with photosensitiser, demonstrated that photoradiation-induced enzyme inhibition was significantly greater in mesothelioma than in R3230AC mammary tumour preparations. However, in parallel studies conducted in vitro, when photosensitiser and light were delivered to previously unperturbed mitochondria, rates of enzyme inhibition were not significantly different. Both tumours were established in long-term cell culture. While the uptake of porphyrin photosensitiser was equivalent in both cell lines, the R3230AC cells displayed a significantly greater photosensitivity than the mesothelioma cells. The data presented here demonstrate that the mechanisms that govern response to photodynamic therapy are complex, but in the case of these two xenografted tumours host response to therapy is not likely to play a significant role.

Activation of macrophages by Photofrin II during photodynamic therapy

In order to obtain information about the activation of macrophages (M phi s) during photodynamic therapy (PDT), the influence of Photofrin II (Pf II) on the viability of thioglycollate-elicited murine M phi s and the subsequent generation of superoxide anion was studied. Irradiations were performed at an energy density of 5 J cm-2, a power density of 150 mW cm-2 and a wavelength of 405 nm. Viability of M phi s was assessed using the acridine orange-ethidium bromide assay. Superoxide anion generation was determined using ferricytochrome c (cyt c) and nitroblue tetrazolium (NBT) reduction. Our results indicate that the M phi s are highly susceptible to PDT as their viability is decreased to approximately 30% by 1 microgram ml-1 Pf II at the energy density indicated above. Within the first 30 min of addition of the photosensitizer, a reducing agent is generated intracellularly by the stimulation of the M phi s. An extracellular release of superoxide anion does not occur, as measured by the cyt c assay. Preincubation of the cells for 1 or 24 h with Pf II and a second challenge with phorbol myristate acetate (PMA) does not enhance the reduction of NBT. Thus, Pf II exerts an immediate effect on the M phi s which could be interpreted as a first step for subsequent reactions.

Gross and microscopic changes in the viscera induced by photodynamic therapy applied to the lower abdomen of intact rats

Photodynamic therapy (PDT) is a promising approach to the treatment of cancer. Preferential retention of the photosensitizer by malignant tissue has been considered a hallmark of this treatment modality. However, photosensitivity can be observed in normal, non-neoplastic tissues, and the present study investigated the effects of PDT treatment on the abdomen of intact rats. A circular region (1 cm diameter) on the shaved abdomen of Fischer rats, pretreated 24 h prior with Photofrin II, was irradiated for 30 min at 632 nm. Control animals received either photoradiation or Photofrin II administration. Subsequent lesions were observed in the irradiated skin, its associated abdominal wall, and the underlying gut in rats receiving Photofrin II and laser irradiation. All tissues were not equally sensitive to PDT treatment. Gut lesions were consistently more severe than were skin and abdominal wall injuries. By 24 hr after treatment, the gut manifested a transmural hemorrhagic necrosis, while the irradiated skin and abdominal wall were edematous, with an inflammatory infiltrate in the dermis and around occasional swollen myocytes. These results indicate that superficial lesions induced by PDT may not be reliable indicators of the extent of deeper PDT tissue damage. Further, it may be possible to take advantage of this discrepancy in tissue sensitivity and treat deep tissues through less sensitive superficial tissues.

Increased efficacy of photodynamic therapy of R3230AC mammary adenocarcinoma by intratumoral injection of Photofrin II

Photodynamic therapy consists of the systemic administration of a derivative of haematoporphyrin (Photofrin II) followed 24-72 h later by exposure of malignant lesions to photoradiation. We investigated the efficacy of this treatment after direct intratumoral injection of Photofrin II. This direct treatment regimen resulted in higher rates of inhibition of mitochondrial cytochrome c oxidase (5.13% J-1 cm-2 x 10(-1) and succinate dehydrogenase (3.14% J-1 cm-2 x 10(-1] in vitro at 2 h after intratumoral injection compared to rates of inhibition obtained after intraperitoneal drug administration: 0.51 and 0.42% J-1 cm-2 x 10(-1), respectively. A significant delay in tumour growth in vivo was observed in animals that received intratumoral injections 2 h before photoradiation compared to animals injected intraperitoneally at either 2 or 24 h before photoradiation. The treatment protocols were compared with control groups, consisting of Photofrin II administration intratumorally or intraperitoneally without photoradiation, or photoradiation in the absence of Photofrin II. These data indicate that the intratumoral injection regimen with Photofrin II enhanced the efficacy of photodynamic therapy. The greater delay in tumour growth observed after intratumoral administration of Photofrin II suggests a mechanism favouring direct cell damage.

Generation of free radicals by photoexcitation of pheophorbide alpha, haematoporphyrin and protoporphyrin

An investigation of the production of radical species by photoexcitation pheophorbide alpha, haematoporphyrin and protoporphyrin was performed. In an aqueous solution containing different amounts of ethanol, the superoxide radical was detected by the spin trapping technique. In addition, secondary radicals were observed. The generation of oxygen radicals was found to dominate in solutions with a low ethanol content.

Prevention of cutaneous phototoxicity in photodynamic therapy

Photodynamic therapy using hematoporphyrin derivative (Hpd), or its semipurified form, dihematoporphyrin ether (DHE), in combination with light, has proven effective in the treatment of several types of neoplasms including squamous cell carcinoma. A major disadvantage of this therapy is the long-term retention of these drugs in skin, which may result in cutaneous phototoxicity for weeks after treatment. Singlet oxygen has been identified as the primary cytotoxic product in the reaction of Hpd and light in vitro. This study demonstrates the protective effect in vivo of the singlet oxygen scavengers 1,3 diphenylisobenzofuran and L-tryptophan on the skin of young rats exposed to light after receiving DHE.

In vitro photosensitization of tumour cell enzymes by photofrin II administered in vivo

The ability of injected Photofrin II, a preparation enriched in hydrophobic dihaematoporphyrin ethers and esters, to photosensitize selected mitochondrial and cytosolic enzymes during illumination in vitro was examined. Preparations of R3230AC mammary tumours, obtained at designated times after a single dose of Photofrin II, displayed a time-dependent photosensitivity. Maximum inhibition of mitochondrial enzymes occurred at 24 hours post-treatment, whereas no inhibition of the cytosolic enzyme, pyruvate kinase, was observed over the 168 hour time course. At the selected 24 hour time point, mitochondrial enzyme photosensitisation was found to be drug dose (5.25 mg kg-1 Photofrin II) and light dose dependent, the rank order of inhibition being cytochrome c oxidase greater than F0F1 ATPase greater than succinate dehydrogenase greater than NADH dehydrogenase. We conclude that porphyrin species contained in Photofrin II accumulate in mitochondria of tumour cells in vivo and produce maximum photosensitisation at 24-72 hours after administration to tumour-bearing animals. The time course observed here with Photofrin II is similar to that seen previously with the more heterogenous haematoporphyrin derivative preparation in this in vivo-in vitro model.

A review of photoradiation therapy in the management of central nervous system tumours

Photoradiation therapy depends on the selective retention of a photosensitizer within the tumour followed by activation of the sensitizer by irradiating the tumour with light of the appropriate wavelength. The present methods of treatment of cerebral glioma are inadequate and the possible benefit of utilizing photoradiation therapy to obtain improved local control of the tumour has been studied in the laboratory and in clinical trials. The biological basis for photoradiation therapy and the laboratory studies and clinical trials involving the use of photoradiation therapy to treat cerebral tumours are discussed.

Photoradiation therapy and its potential in the management of neurological tumors

Photoradiation therapy is a form of local treatment that depends on the selective retention of a photosensitizer, such as hematoporphyrin derivative (HpD), by the tumor followed by treatment with light of an appropriate wavelength to activate the sensitizer in the tumor. The selective uptake of HpD by cerebral tumors has been demonstrated both in laboratory animal model studies and in clinical studies, and selective destruction of intracerebral tumors has been demonstrated in animal glioma models. The biological basis for photoradiation therapy and, in particular, the mechanisms for the selective uptake of the sensitizer into the tumor and the destruction of tumor with photoradiation therapy are discussed. Current evidence suggests that singlet oxygen is the major intermediary leading to cell damage, although other radicals such as hydrogen peroxide and hydroxyl radicals may be involved. Other studies suggest that the initial damage is to the blood vessels, and the tumor subsequently undergoes ischemic changes. Sixty-four patients treated with photoradiation therapy have been reported in the literature. The initial clinical studies were disappointing in their therapeutic effect but these studies often included treatment of recurrent gliomas and low doses of light were used. Technical advances, particularly in laser technology, have enabled more effective photoradiation therapy and the clinical trials are reviewed.

Transformation and mutagenic potential of porphyrin photodynamic therapy in mammalian cells

The transformation and mutagenic potential of porphyrin photodynamic therapy has been examined in mammalian cells. The mutagenic frequency in Chinese hamster cells at the Na+/K+ ATPase locus was measured by resistance to ouabain following treatment with either photodynamic therapy (PDT) or UV irradiation. The C3H 10T 1/2 mouse embryo cell system was used to document the transformation frequency following PDT, UV irradiation, gamma irradiation or exposure to 3-methylcholanthrene (MCA). Treatments with UV irradiation were effective in producing mutants resistant to ouabain, and treatments with UV irradiation, gamma irradiation and MCA generated transformants at frequencies comparable to those which are reported in the literature. However, PDT treatment conditions (which produced a full range of cytotoxicity) did not induce any mutagenic or transformation activity above background levels.

The one-electron reduction of uroporphyrin I by rat hepatic microsomes

Uroporphyrin I, which accumulates in body tissues of congenital erythropoietic porphyria patients, can undergo an enzymatic one-electron reduction to the porphyrin anion radical when a suitable reducing cofactor is present. We have demonstrated, in the absence of light, that anaerobic microsomal incubations containing NADPH and uroporphyrin I give an electron spin resonance spectrum consistent with the enzymatic formation of a porphyrin anion free radical. This radical undergoes a second-order decay (k2 approximately 10(5) M-1 s-1) due to nonenzymatic disproportionation of the radical. Aerobic microsomal incubations were also investigated for the reduction of oxygen to superoxide by monitoring oxygen consumption and the spin-trapping of superoxide. These experiments demonstrate that electron transfer from the porphyrin radical to molecular oxygen does occur, but due to the slow formation of the radical anion, no oxygen consumption above the basal level could be detected in the microsomal incubations. The photoreduction of uroporphyrin I in aerobic and anaerobic incubations was also investigated.

Superoxide, hydrogen peroxide and singlet oxygen in hematoporphyrin derivative-cysteine, -NADH and -light systems

Hematoporphyrin derivative and light in the presence of cysteine or glutathione were found to convert oxygen to superoxide and hydrogen peroxide at pH less than approx. 6.5, while at pH greater than 6.5 no superoxide or hydrogen peroxide production was observed. However, at pH values greater than 6.5 the rate of oxygen consumption increased. This rate paralleled the acid dissociation curve of the cysteine thiol group and is consistent with the chemical quenching of 1O2 by cysteine. The superoxide and hydrogen peroxide formation observed below pH 6.5 appeared not to be related to the singlet oxygen production of hematoporphyrin derivative. In addition, superoxide and hydrogen peroxide production was observed with hematoporphyrin derivative and light in the presence of NADH, both above and below pH 6.5. Direct detection of singlet oxygen luminescence at 1268 nm in the hematoporphyrin derivative-light system (2H2O as solvent) revealed an apparent linear increase in the singlet oxygen emission intensity as the p2H was raised from 7.0 to 10.0. Azide efficiently quenched this observed emission. In addition, at p2H 7.4, 1 mM cysteine resulted in a 40% reduction of the singlet oxygen luminescence, while at p2H 9.4 the signal was quenched by over 95% (under the experimental conditions employed). In total, we interpret these results as consistent with the chemical quenching of 1O2 by the ionized thiol group of cysteine.

[Activated radical species of oxygen]

Oxygen free radicals are often formed during photosensitization processes. Kinetic and thermodynamical characteristics are briefly described for OH and O2-. radicals.