Verteporfin: a milestone in opthalmology and photodynamic therapy

During the past year, a photosensitiser named benzoporphyrin derivative (BPD) has been approved in 26 countries under the generic name verteporfin (Visudynetrade mark, Novartis), for the treatment of patients with a certain type of the wet form of age-related macular degeneration (AMD) by photodynamic therapy (PDT). AMD is the leading cause of blindness in the developed world, with approximately half a million new cases of the wet form per year. The approval of Visudynetrade mark therapy represents a major milestone in ophthalmology since AMD was previously untreatable by any modality which would preserve existing vision. It was also a milestone in the development of PDT, not only because it represented the first breakthrough in the use of PDT to treat an otherwise untreatable condition, but also because it represented the first mass market for a PDT treatment where prospects of a substantial financial return on many years of investment appear to be likely. In this article, we look at the background to the development of BPD, primarily for its use in AMD, but also in other applications.

5-Aminolaevulinic acid methyl ester transport on amino acid carriers in a human colon adenocarcinoma cell line

The transport mechanisms of 5-aminolevulinic acid methyl ester (5-ALA-ME) have been studied in a human adenocarcinoma cell line (WiDr) by means of 14[C]-labeled 5-ALA-ME. The transport was found to be partly Na+ dependent, while the extracellular Cl- concentration did not affect the uptake. The transport of 5-ALA-ME into WiDr cells was dependent on the incubation temperature and was found to be completely blocked by the inhibitors of energy metabolism, 2-deoxyglucose and sodium azide. WiDr cells were treated with 10 mM of 14 different amino acids and the substrate specificity of the 5-ALA-ME transporter(s) was analyzed by treating the cells with 23 microM or 1 mM 14[C]-labeled 5-ALA-ME. The transport of 5-ALA-ME was found to be inhibited to the highest extent, i.e. about 60%, by the nonpolar amino acids L-alanine, L-methionine, L-tryptophan and glycine. The uptake of 5-ALA-ME followed an exponential decay with increasing concentration of glycine, reaching a maximum inhibition of uptake of 5-ALA-ME of 55%. Sarcosine, a specific inhibitor of system Gly, did not significantly inhibit 5-ALA-ME transport. In contrast to transport of 5-ALA, 5-ALA-ME does not seem to be taken up by system BETA transporters. In conclusion, the cellular uptake of 5-ALA-ME into WiDr cells seems to be due to active transport mechanisms, involving transporters of nonpolar amino acids.

Investigation of cross-resistance to a range of photosensitizers, hyperthermia and UV light in two radiation-induced fibrosarcoma cell strains resistant to photodynamic therapy in vitro

Two distinct photodynamic therapy-resistant variants of the murine radiation-induced fibrosarcoma (RIF) cell line have been isolated. One strain displayed relative resistance over the parental RIF-1 strain to treatment with the porphyrin-based compound, polyhaematoporphyrin (PHP), whereas the other strain displayed relative resistance over the RIF-1 strain to treatment using the cationic zinc (II) pyridinium-substituted phthalocyanine (PPC). The PHP-resistant strain did not display cross-resistance to PPC-mediated treatment, and vice versa. In both PDT-resistant strains, the increased resistance could not be attributed to altered cellular growth rate, antioxidant capacity or intracellular sensitizer localization. The PHP-resistant strain displayed resistance to treatment with both short (1 h) and extended (16 h) sensitizer incubation periods, which may indicate that in this strain, the resistance has arisen through an alteration in a membrane component. Conversely, the PPC-resistant strain only displayed increased resistance over the parental cells to treatment involving the short drug incubation, which is likely to reflect the existence of a threshold effect caused by the alteration of an individual cellular target. Each resistant strain has been compared to the parental strain in terms of cellular sensitivity to treatment with a range of other photosensitizers, hyperthermia, UV light and the anticancer agent cis-diamminedichloroplatinum. The PHP-resistant strain exhibited crossresistance to photosensitization treatment using exogenously added protoporphyrin IX, and also to treatment with the anionic phthalocyanine sensitizers, zinc (II) tetrasulfonated phthalocyanine and zinc (II) tetraglycine-substituted phthalocyanine. The PPC-resistant strain did not display cross-resistance to any of the treatment strategies employed in this investigation. The results of this investigation indicate that there are at least two distinct mechanisms of PDT resistance in RIF cells, and that the mechanism of PHP resistance may, to some extent depend, upon the physical nature of the sensitizer molecule.

Decreased efficiency of trypsinization of cells following photodynamic therapy: evaluation of a role for tissue transglutaminase

Identifying the cellular responses to photodynamic therapy (PDT) is important if the mechanisms of cellular damage are to be fully understood. The relationship between sensitizer, fluence rate and the removal of cells by trypsinization was studied using the RIF-1 cell line. Following treatment of RIF-1 cells with pyridinium zinc (II) phthalocyanine (PPC), or polyhaematoporphyrin at 10 mW cm-2 (3 J cm-2), there was a significant number of cells that were not removed by trypsin incubation compared to controls. Decreasing the fluence rate from 10 to 2.5 mW cm-2 resulted in a two-fold increase in the number of cells attached to the substratum when PPC used as sensitizer; however, with 5,10,15,20 meso-tetra(hydroxyphenyl) chlorine (m-THPC) there was no resistance to trypsinization following treatment at either fluence rate. The results indicate that resistance of cells to trypsinization following PDT is likely to be both sensitizer and fluence rate dependent. Increased activity of the enzyme tissue-transglutaminase (tTGase) was observed following PPC-PDT, but not following m-THPC-PDT. Similar results were obtained using HT29 human colonic carcinoma and ECV304 human umbilical vein endothelial cell lines. Hamster fibrosarcoma cell (Met B) clones transfected with human tTGase also exhibited resistance to trypsinization following PPC-mediated photosensitization; however, a similar degree of resistance was observed in PDT-treated control Met B cells suggesting that tTGase activity alone was not involved in this process.

Routine double treatments of superficial basal cell carcinomas using aminolaevulinic acid-based photodynamic therapy

BACKGROUND

Superficial basal cell carcinomas of the skin (sBCC) often respond poorly to single-treatment aminolaevulinic acid-based photodynamic therapy (ALA-PDT), with a number of reports indicating a relapse rate of 50% or more.

OBJECTIVES

To determine whether a second treatment at seven days can improve the response.

METHODS

Twenty-six lesions were treated twice with ALA-PDT, with an interval of 7 days between the two treatment sessions.

RESULTS

We observed a complete response rate of 100% 1 month after treatment. Only one lesion relapsed (16 months post-PDT), a relapse rate of 4% (median follow up 27 months; range 15-45 months). Cosmetic results were excellent.

CONCLUSIONS

We consider routine double treatments with ALA-PDT to be an effective approach to the management of sBCC, particularly those located in anatomically difficult, or cosmetically sensitive, sites.

Overexpression of cyclin D1 occurs frequently in human pancreatic endocrine tumors

The molecular pathogenesis of human pancreatic endocrine tumors (PETs) is poorly understood. Three independent animal models have pointed to the pivotal role of the G1/S cell cycle transition in pancreatic endocrine cell proliferation. We thus hypothesized that the cell cycle regulator cyclin D1 may contribute to the pathogenesis of human PETs. Overexpression of cyclin D1 was identified in 43% of cases, and no correlation was observed with clinical phenotype. The novel observation of frequent overexpression of cyclin D1 suggests that this established oncogene may be implicated in the pathogenesis of human PETs. The absence of detectable alterations in cyclin D1 genomic structure suggests that the mechanism for its oncogenic activation in PETs may be transcriptional or posttranscriptional.

Comparison of the pharmacokinetics and phototoxicity of protoporphyrin IX metabolized from 5-aminolevulinic acid and two derivatives in human skin in vivo

Our novel approach was to compare the pharmacokinetics of 5-aminolevulinic acid (ALA), ALA-n-butyl and ALA-n-hexylester induced protoporphyrin IX (PpIX), together with the phototoxicity after photodynamic therapy (PDT) in human skin in vivo, using iontophoresis as a dose-control system. A series of four increasing doses of each compound was iontophoresed into healthy skin of 10 volunteers. The kinetics of PpIX metabolism (n = 4) and the response to PDT (n = 6) performed 5 h after iontophoresis, were assessed by surface PpIX fluorescence and post-irradiation erythema. Whilst ALA-induced PpIX peaked at 7.5 h, highest PpIX fluorescence induced by ALA-n-hexylester was observed at 3-6 h and no clear peak was seen with ALA-n-butylester. With ALA-n-hexylester, more PpIX was formed after 3 (P < 0.05) and 4.5 h, than with ALA or ALA-n-butylester. All compounds showed a linear correlation between logarithm of dose and PpIX fluorescence/phototoxicity at 5 h, with R-values ranging from 0.87 to 1. In addition, the ALA-n-hexylester showed the tendency to cause greater erythema than ALA and ALA-n-butylester. Fluorescence microscopy (n = 2) showed similar PpIX distributions and penetration depths for the three drugs, although both ALA esters led to a more homogeneous PpIX localization. Hence, ALA-n-hexylester appears to have slightly more favorable characteristics for PDT than ALA or ALA-n-butylester.

Effect of photodynamic therapy on recurrent pituitary adenomas: clinical phase I/II trial--an early report

Pituitary adenomas, although histologically benign, are not always curable by surgery alone, principally because of dural infiltration, as well as their peculiar anatomical location. Radiotherapy has been employed as an adjuvant therapy to address residual disease with favourable results. This approach is, however, not without side effects, and it cannot be repeated. We are therefore investigating the effectiveness of photodynamic therapy (PDT) on recurrent pituitary adenomas in humans. This study details the protocol applied to 12 patients with recurrent pituitary adenomas, which involved systemic administration of photosensitizer (Photofrin) followed, after a period of 24-48 h, by intraoperative illumination of the tumour bed using 630 nm laser light. The primary end points were visual, endocrine and radiological improvement. The incidence of side effects was also monitored. The longest follow-up is 2 years. Most patients suffering from visual acuity or field defects have shown improvement when followed for 12 months or more. Three patients showed complete recovery of their visual fields. All those who presented with functional adenomas have shown reduction in their hormone levels. Tumour volume, relative to the preoperative size, was 122, 87, 66, 60 and 46% at 4 days, and 3, 6, 18 and 24 months, respectively. One patient developed severe skin photosensitization due to early exposure to direct sunlight and three others displayed minor skin reactions. There was no treatment-related mortality or morbidity. One patient (operated transcranially) developed hemiparesis postoperatively, which recovered completely. We think this is unrelated to the treatment. This prospective study demonstrates that PDT may be safely applied to the pituitary fossa by the trans-sphenoidal route and indicates the need for a randomized, controlled trial in order to establish its therapeutic potential.

Mechanism of uptake of a cationic water-soluble pyridinium zinc phthalocyanine across the outer membrane of Escherichia coli

Previous studies have shown that a cationic water-soluble pyridinium zinc phthalocyanine (PPC) is a powerful photosensitizer that is able to inactivate Escherichia coli. In the current work incubation of E. coli cells with PPC in the dark caused alterations in the outer membrane permeability barrier of the cells, rendering the bacteria much more sensitive to hydrophobic compounds, with little effect seen with hydrophilic compounds. Addition of Mg(2+) to the medium prior to incubation of the cells with PPC prevented these alterations in the outer membrane permeability barrier. The presence of Mg(2+) in the medium also prevented the photoinactivation of E. coli cells with PPC. These results are consistent with the hypothesis that PPC gains access across the outer membrane of E. coli cells via the self-promoted uptake pathway, a mechanism of uptake postulated for the uptake of other cationic compounds across the outer membranes of gram-negative bacteria.

Constitutive death of platelets leading to scavenger receptor-mediated phagocytosis. A caspase-independent cell clearance program

Apoptosis is a physiological program for the deletion of cells in which caspases govern events leading to safe clearance by phagocytes. However, a growing weight of evidence now suggests that not all forms of programmed cell death are caspase-dependent. We now report a complete and constitutive but caspase-independent program for the specific phagocytic clearance of intact effete platelets, anucleated blood cells of critical importance in health and disease. Platelets aged in vitro not only exhibited increased expression of proapoptotic Bak and Bax but also evidenced constitutive diminution of function such as decreased aggregation to ADP, which was accelerated by culture in the absence of plasma. This abrogation of cell function in plasma-deprived platelets was associated with morphological and biochemical features similar to those of granulocyte apoptosis, that is, cytoplasmic condensation, plasma membrane changes including exposure of phosphatidylserine and the granule protein P-selectin, and recognition by phagocyte scavenger receptors. However, and in contrast with constitutive death of other inflammatory blood cells by apoptosis, these events were not affected by caspase inhibitors, nor was there evidence of caspase-3 activation either by hydrolysis of analog peptide substrates or Western blot analysis, serving to emphasize that neither programmed cell death nor clearance by phagocytes need involve caspases.

Vitamin D receptor as a candidate tumor-suppressor gene in severe hyperparathyroidism of uremia

Most chronic renal failure patients with severe refractory hyperparathyroidism harbor at least one monoclonal parathyroid tumor, but the specific acquired genetic defects that confer this clonal selective advantage remain poorly understood. Somatic inactivation of the vitamin D receptor (VDR) gene could contribute to clonal outgrowth, because a parathyroid cell containing this lesion would have an impaired response to the antiproliferative influence of 1,25-dihydroxyvitamin D3. Furthermore, diminished expression of VDR protein has been described in uremia-associated parathyroid tumors. Therefore, to assess VDR gene inactivation's potential pathogenetic role in this disease, we rigorously analyzed the VDR gene in 59 parathyroid tumors surgically resected from uremic patients. First, Southern blotting and/or PCR analyses of 29 tumor samples from 14 genetically informative patients revealed no allelic losses at the VDR locus. Next, direct DNA sequencing of all VDR splice junctions, associated intronic sequences, and virtually the entire VDR-coding region for all 59 tumors revealed no acquired mutations. Last, 37 tumor DNA samples were subjected to comparative genomic hybridization, and no chromosomal losses in the VDR region (12cen-q12) were observed. These observations suggest that inactivating defects within the VDR gene do not commonly contribute to the primary pathogenesis of severe refractory hyperparathyroidism in uremia.

Photodynamic therapy using 5-aminolaevulinic acid for oesophageal adenocarcinoma associated with Barrett's metaplasia

Photodynamic therapy (PDT) is a novel technique for local endoscopic treatment of gastrointestinal neoplasia. Current photosensitisers for PDT may cause prolonged skin phototoxicity. 5-Aminolaevulinic acid (ALA), a precursor of the photosensitiser protoporphyrin IX (PpIX), is more acceptable because of its short half-life and preferential accumulation in mucosa and mucosal tumour. We have treated 12 patients, median age 73 years (range 55-88) with oesophageal adenocarcinoma arising from Barrett's metaplasia (two carcinomas-in-situ, grade 0; 10 carcinomas, grade 1-11A based on endoluminal ultrasound in two and CT scanning in 10 patients). ALA (60 and 75 mg/kg body weight) was given orally in two or five equally divided doses. The PpIX distribution in stomach, normal oesophagus, Barrett's mucosa and carcinoma was measured by quantitative fluorescence photometry. PDT was performed using laser light (630 nm) delivered via a cylindrical diffuser 4-6 h after the first dose of ALA. The patients received one to four sessions of PDT. PpIX accumulation in the mucosa was two to three times that in the lamina propria. The differential distribution between carcinomatous and normal oesophageal mucosa was less marked (carcinoma:normal mucosa ratio = 1.4). Higher doses of ALA increased PpIX accumulation in all tissues but did not increase the differential PpIX distribution between tumour and normal oesophageal mucosa. After PDT using ALA (ALA/PDT), all mucosa showed superficial white necrotic changes and the histology confirmed fibrinoid necrosis. One patient with carcinoma-in-situ had the tumour eradicated after one treatment with no recurrence at 28 months. Another patient with a small T1 tumour required four ALA/PDT treatments, and died of other disease after 36 months. There was no evidence of recurrence. The tumour bulk in the other carcinomas was not significantly reduced. ALA/PDT has a potential for the eradication of small tumours but careful patient selection with endoluminal ultrasound is needed when using ALA/PDT to treat oesophageal cancer.

Improved response of plaque psoriasis after multiple treatments with topical 5-aminolaevulinic acid photodynamic therapy

We investigated the clinical response of 10 patients with plaque psoriasis to multiple treatments with photodynamic therapy, using topical application of 5-aminolaevulinic acid followed by exposure to broad-band visible radiation. Treatment was performed up to 3 times per week, with a maximum of 12 treatments, using a light dose of 8 Jcm(-2) delivered at a dose-rate of 15 mW cm(-2). Eight patients showed a clinical response. Out of 19 treated sites, 4 cleared, 10 responded but did not clear and 5 showed no improvement. Of the 4 sites that cleared only 1 did so fully, after 7 treatments, 45 days after the start of therapy. Of the 10 sites that responded partially, the greatest reduction in scale, erythema and induration index occurred after a minimum of 3 and a maximum of 8 treatments. The intensity of 5-aminolaevulinic acid-induced protoporphyrin IX fluorescence, recorded prior to the first treatment, varied between sites on the same patient as well as between patients. There was also a variation in fluorescence intensity recorded from the same site immediately prior to subsequent treatments, although the pretreatment levels generally decreased as the study progressed and then increased as psoriasis relapsed. Biopsies confirmed that fluorescence was localized throughout the epidermis and stratum corneum, but the level was not consistent between sections taken within the same biopsy. We also observed fluorescence at sites distant from the ones that received 5-aminolaevulinic acid, which was not present prior to the start of the treatment programme, but found no evidence of elevated levels of plasma porphyrins. The level of discomfort associated with this therapy increased with increasing values of the calculated photodynamic dose, defined as the product of the initial photosensitizer concentration and the percentage reduction in fluorescence following irradiation. Therefore, although clinical efficacy improved with multiple treatments, unpredictable response and patient discomfort make ALA-PDT unsuitable for the treatment of psoriasis.

31P magnetic resonance spectroscopy as a predictor of efficacy in photodynamic therapy using differently charged zinc phthalocyanines

Photodynamic therapy (PDT) is a developing approach to the treatment of solid tumours which requires the combined action of light and a photosensitizing drug in the presence of adequate levels of molecular oxygen. We have developed a novel series of photosensitizers based on zinc phthalocyanine which are water-soluble and contain neutral (TDEPC), positive (PPC) and negative (TCPC) side-chains. The PDT effects of these sensitizers have been studied in a mouse model bearing the RIF-1 murine fibrosarcoma line studying tumour regrowth delay, phosphate metabolism by magnetic resonance spectroscopy (MRS) and blood flow, using D2O uptake and MRS. The two main aims of the study were to determine if MRS measurements made at the time of PDT treatment could potentially be predictive of ultimate PDT efficacy and to assess the effects of sensitizer charge on PDT in this model. It was clearly demonstrated that there is a relationship between MRS measurements during and immediately following PDT and the ultimate effect on the tumour. For all three drugs, tumour regrowth delay was greater with a 1-h time interval between drug and light administration than with a 24-h interval. In both cases, the order of tumour regrowth delay was PPC > TDEPC = TCPC (though the data at 24 h were not statistically significant). Correspondingly, there were greater effects on phosphate metabolism (measured at the time of PDT or soon after) for the 1-h than for the 24-h time interval. Again effects were greatest with the cationic PPC, with the sequence being PPC > TDEPC > TCPC. A parallel sequence was observed for the blood flow effects, demonstrating that reduction in blood flow is an important factor in PDT with these sensitizers.

Does an association between pesticide use and subsequent declines in catch of Atlantic salmon (Salmo salar) represent a case of endocrine disruption?

Historical aerial applications of the insecticide Matacil 1.8D provide an opportunity to look for potential effects of the endocrine disrupting compound 4-nonylphenol (4-NP) on Atlantic salmon (Salmo salar) populations. Matacil 1.8D contained the carbamate insecticide aminocarb, with 4-NP as primary solvent. Between 1975 and 1985 Matacil 1.8D was applied to forests in Atlantic Canada to control damage from the spruce budworm (Choristoneura fumiferana). After spraying, estimated concentrations of 4-NP in water fell within a range in which estrogenic effects might be anticipated. The spraying coincided with final stages of smolt development in salmon. Salmon catch data were evaluated considering effects on survival of the smolt stage. There was a significant negative relationship between the returns of salmon and the proportion of tributaries sprayed within the Restigouche River drainage basin in 1977. There was also a broader event of unusually heavy salmon smolt mortality in 1977, which contains a significant relationship indicating that where Matacil 1.8D spraying occurred, the smolt mortality increased. For 16 rivers exposed to spraying between 1973 and 1990, a significant proportion (p<0.005) of the lowest salmon catches coincided with Matacil 1.8D spraying. A decline coinciding with the use of Matacil 1.8D was also apparent in blueback herring (Alosa aestivalis) catches in New Brunswick. Because similar relationships were not evident for Matacil 1.8F or fenitrothion, neither of which were formulated with 4-NP, we hypothesize that the 4-NP in Matacil 1.8D was the causal agent. Concentrations of 4-NP described here are within current ranges encountered in industrial effluents and municipal sewage outfalls.

Identification and partial characterization of an unusual distribution of the photosensitizer meta-tetrahydroxyphenyl chlorin (temoporfin) in human plasma

Temoporfin (m-THPC) is an extremely powerful photosensitizing drug, more than 100-fold more photocytotoxic than Photofrin and many other drugs. The reasons for this are not yet known but are likely to be associated with the mechanism of uptake of the drug and its intratumoral and intracellular localization. Uptake itself is likely to be dependent upon the plasma binding of the drug following administration. In the current work, we have shown that the addition of m-THPC to human plasma in vitro at clinically relevant doses of sensitizer and administration solvent (diluant) gives rise to a protein-binding pattern quite different to that of Photofrin and other hydrophobic drugs as judged by density-gradient ultracentrifugation. Analysis of the binding immediately after addition to human plasma has shown that lipoprotein binding accounts for only a minor proportion of the sensitizer, which is mainly associated with a high-density protein fraction that is not coincident with serum albumin. The m-THPC protein complex does not fluoresce significantly even on dilution. This binding pattern is highly dependent on administration conditions and storage. Over a period of 6-8 h at 37 degrees C the m-THPC that is associated with this unidentified fraction redistributes to the plasma lipoproteins. Plasma collected from rats after intravenous administration of m-THPC also contains this low fluorescent complex, showing that this phenomenon is not limited to human plasma and also occurs in vivo. It is postulated that the m-THPC bound to the unknown protein fraction is highly aggregated and that it is likely to be taken up into tissues in this form. This unusual uptake may possibly be associated with the very high activity of m-THPC and also to the recent finding of a second peak in the plasma pharmacokinetics of the drug.

A comparative study of the cellular uptake and photodynamic efficacy of three novel zinc phthalocyanines of differing charge

Three novel substituted zinc (II) phthalocyanines (one anionic, one cationic and one neutral) were compared to two clinically used photosensitizers, 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (m-THPC) and polyhematoporphyrin (PHP), as potential agents for photodynamic therapy (PDT). Using the RIF-1 cell line, photodynamic efficacy was shown to be related to cellular uptake. The cationic phthalocyanine (PPC, pyridinium zinc [II] phthalocyanine) had improved activity over the other two phthalocyanines and slightly improved activity over PHP and m-THPC. The initial subcellular localization of each photosensitizer was dependent upon the hydrophobicity and plasma protein binding. The phthalocyanines had a punctate distribution indicative of lysosomes, whereas m-THPC and PHP had a more diffuse cytoplasmic localization. A relocalization of phthalocyanine fluorescence was observed in some cases following low-level light exposure, and this was charge dependent. The anionic phthalocyanine (TGly, tetraglycine zinc [II] phthalocyanine) relocalized to the nuclear area, the localization of the hydrophobic phthalocyanine (TDOPc, tetradioctylamine zinc [II] phthalocyanine) was unchanged, whereas the distribution of the cationic phthalocyanine (PPC) became more cytoplasmic. This suggests that relocalization following low-level irradiation is a critical factor governing efficacy, and a diffuse cytoplasmic distribution may be a determinant of good photodynamic activity.

The high photoactivity of m-THPC in photodynamic therapy. Unusually strong retention of m-THPC by RIF-1 cells in culture

5,10,15,20-Tetra(m-hydroxyphenyl)chlorin (m-THPC, Foscan) is an extremely powerful photosensitizer showing up to 200 times the photodynamic activity of Photofrin in patients, in terms of drug/light dose. The influence of treatment conditions on the photodynamic efficacy of m-THPC has been compared to polyhematoporphyrin (PHP), a Photofrin equivalent, and a cationic pyridinium zinc (II) phthalocyanine (PPC), using the RIF-1 cell line. As predicted, the presence of serum during sensitizer incubation reduced the photodynamic efficacy of all three sensitizers. However, the presence of serum during the illumination period only had an inhibitory effect with PHP and PPC but not m-THPC. Quantification of the intracellular levels of sensitizer revealed that this was due to the efflux of PPC and PHP but not m-THPC into the medium, suggesting that m-THPC is tightly sequestered on entering the cell. This may partially explain the high efficacy of m-THPC in clinical photodynamic therapy and also highlights the importance not only of incubation conditions but also illumination conditions when in vitro comparisons are performed.

Protoporphyrin IX fluorescence photobleaching during ALA-mediated photodynamic therapy of UVB-induced tumors in hairless mouse skin

Fluorescence photobleaching of protoporphyrin IX (PpIX) during superficial photodynamic therapy (PDT), using 514 nm excitation, was studied in UVB-induced tumor tissue in the SKH-HR1 hairless mouse. The effects of different irradiance and light fractionation regimes upon the kinetics of photobleaching and the PDT-induced damage were examined. Results show that the rate of PpIX photobleaching (i.e., fluorescence intensity vs fluence) and the PDT damage both increase with decreasing irradiance. We have also detected the formation of fluorescent PpIX photoproducts in the tumor during PDT, although the quantity recorded is not significantly greater than generated in normal mouse skin, using the same light regime. The subsequent photobleaching of the photoproducts also occurs at a rate (vs fluence) that increases with decreasing irradiance. In the case of light fractionation, the rate of photobleaching increases upon renewed exposure after the dark period, and there is a corresponding increase in PDT damage although this increase is smaller than that observed with decreasing irradiance. The effect of fractionation is greater in UVB-induced tumor tissue than in normal tissue and the damage is enhanced when fractionation occurs at earlier time points. We observed a variation in the distribution of PDT damage over the irradiated area of the tumor: at high irradiance a ring of damage was observed around the periphery. The distribution of PDT damage became more homogeneous with both lower irradiance and the use of light fractionation. The therapeutic dose delivered during PDT, calculated from an analysis of the fluorescence photobleaching rate, shows a strong correlation with the damage induced in normal skin, with and without fractionation. The same correlation could be made with the data obtained from UVB-induced tumor tissue using a single light exposure. However, there was no such correlation when fractionation schemes were employed upon the tumor tissue.

Phagocytosis triggers macrophage release of Fas ligand and induces apoptosis of bystander leukocytes

Human monocyte/macrophages (Mphi) exposed to nonparticulate stimuli can express cell surface Fas ligand (FasL) and release active soluble FasL (sFasL). We now report that monocyte/Mphi-ingesting opsonized zymosan released sFasL and conditioned supernatants so that these triggered Fas-mediated apoptosis of "bystander" monocytes and FasL-negative neutrophils. Furthermore, identical results were seen with Mphi taking up apoptotic neutrophils, whereas medium conditioned by Mphi phagocytizing latex beads had no proapoptotic effects upon neutrophils despite the presence of sFasL. These data suggest the hitherto unrecognized existence of a feedback loop requiring soluble factors in addition to sFasL that may promote resolution of inflammation-phagocytic clearance of apoptotic cells leading to Fas-mediated killing of bystander leukocytes by phagocytizing macrophages.

Maternal blood, egg and larval thiamin levels correlate with larval survival in landlocked Atlantic salmon

A link was previously established between the Cayuga syndrome, a condition causing 100% mortality in larval landlocked Atlantic salmon, Salmo salar, in several of New York's Finger Lakes, and a maternal diet of alewife, Alosa pseudoharengus, a non-native thiaminase-rich Clupeid fish. We evaluated salmon larvae viability relative to maternal thiamin status, and investigated the putative link of the Cayuga syndrome to an alewife diet in fish from the geographic regions outside the Finger Lakes/lower Great Lakes watersheds. We identified Cayuga syndrome in Atlantic salmon from Otsego Lake in the Susquehanna River watershed and from Green Pond in New York's Adirondack Mountains. In both systems alewife represent the major component of the diet for the salmon. Thiamin levels in the maternal blood of Otsego salmon with syndrome-negative progeny were three- to four-fold greater than those Otsego females whose progeny exhibited 100% mortality. Thiamin levels in eggs and larvae were directly related to thiamin levels in maternal blood in both syndrome-positive and syndrome-negative stocks. Thiamin bath treatments of syndrome-afflicted larvae eliminated mortality regardless of their lake stock of origin. Maternal blood levels of approximately 0.31 nmol thiamin pyrophosphate/g or 0.44 nmol total thiamin/g appear necessary to achieve egg threshold levels of approximately 0.8 and 1.1 nmol/g unphosphorylated and total thiamin, respectively; these egg thiamin levels should prevent significant syndrome-related mortality in landlocked Atlantic salmon larvae. These results confirm the role of thiamin in the etiology of the Cayuga syndrome and support the dietary link of this naturally occurring thiamin deficiency to the thiaminase-rich alewife.

Constitutive apoptosis in human neutrophils requires synergy between calpains and the proteasome downstream of caspases

Programmed cell death invariably requires the activation of proteolytic cascades that are not yet well defined but are initiated after apical caspase activation. We provide evidence that calpains and the proteasome function synergistically downstream of caspases to assist the constitutive apoptotic program of aging neutrophils, which plays an important role in resolution of inflammatory responses. Inhibitor studies indicated that "tethering" of preapoptotic senescent neutrophils to human macrophages required caspase activity. However, the development of morphological features characteristic of apoptosis, including nuclear morphology, PS exposure, surface protein shedding, and the capacity to be ingested by macrophages, required the downstream action of either calpains or the proteasome. Calpain activities were constitutively active in freshly isolated neutrophils and responsible for rearrangements in the protein composition and structure of the plasmalemmal cytoskeleton as they aged in culture and underwent apoptosis. This included a dissociation of protein(s) from F-actin, a candidate mechanism for increased susceptibility to cleavage, and a loss in immunodetectable alpha-actinin and ezrin, two actin-binding, membrane-anchoring proteins. These results clarify roles for different classes of proteases in a physiologically important form of constitutive apoptosis.

The characterisation of three substituted zinc phthalocyanines of differing charge for use in photodynamic therapy. A comparative study of their aggregation and photosensitising ability in relation to mTHPC and polyhaematoporphyrin

Three substituted zinc (II) phthalocyanines (one anionic, one cationic and one hydrophobic) have been compared to two clinically used photosensitisers, 5,10,15,20-tetra (m-hydroxyphenyl) chlorin (mTHPC) and polyhaematoporphyrin (PHP), as potential agents for photodynamic therapy (PDT). Oxygen-consumption experiments, performed to follow the photo-oxidation of tryptophan, histidine and bovine serum albumin (BSA), suggest that the anionic phthalocyanine is the most efficient photosensitiser. The efficacy of BSA oxidation is much greater than that of tryptophan or histidine, which is partly due to monomerisation of the sensitisers upon binding to BSA. Spectra recorded in aqueous solution reveal that all five compounds are highly aggregated, but monomerisation is induced upon the addition of BSA or methanol. Using a range of methanol-buffer solutions, the aggregation state has been directly related to the efficacy of tryptophan photo-oxidation with maximal rates of oxidation achieved when the sensitiser is monomeric. Using erythrocytes as a simple membrane model, the efficacy of each sensitiser exhibits a different trend from that predicted by oxygen-consumption experiments. The anionic phthalocyanine is the least effective at photohaemolysis, whereas the cationic and hydrophobic phthalocyanines have improved activity over PHP and mTHPC.

Localization of putative tumor suppressor loci by genome-wide allelotyping in human pancreatic endocrine tumors

Only two tumor suppressor gene loci, one on 3p25 and the MEN1 gene on 11q13, have thus far been implicated in the pathogenesis of sporadic human pancreatic endocrine tumors (PETs). A genome-wide allelotyping study of 28 human PETs was undertaken to identify other potential tumor suppressor gene loci. In addition to those on chromosomes 3p and 11q, frequent allelic deletions were identified on 3q (32%), 11p (36%), 16p (36%), and 22q (29%). Finer deletion mapping studies localized the smallest regions of common deletion to 3q27, 11p13, and 16p12.3-13.11. Potential candidate genes at these loci include WT1 (11p13), TSC2 (16p13), and NF2 (22q12), but no known tumor suppressor gene localizes to 3q27. The mean fractional allelic loss among these human PETs is 0.126, and no correlation was observed between allelic loss and clinical parameters, including age, sex, hormonal subtype, and disease stage. These findings highlight novel locations of tumor suppressor gene loci that contribute to the pathogenesis of human PETs, and several of these on 3p, 3q, and 22q are syntenic with loci on mouse chromosomes 9 and 16 that are implicated in a murine transgenic model of PETs.