Preclinical Study of Antineoplastic Sinoporphyrin Sodium-PDT via In Vitro and In Vivo Models

Photodynamic therapy (PDT) investigations have seen stable increases and the development of new photosensitizers is a heated topic. Sinoporphyrin sodium is a new photosensitizer isolated from Photofrin. This article evaluated its anticancer effects by clonogenic assays, MTT assays and xenograft experiments in comparison to Photofrin. The clonogenicity inhibition rates of sinoporphyrin sodium-PDT towards four human cancer cell lines ranged from 85.5% to 94.2% at 0.5 μg/mL under 630 nm irradiation of 30 mW/cm² for 180 s. For MTT assays, the IC₅₀ ranges of Photofrin-PDT and sinoporphyrin sodium-PDT towards human cancer cells were 0.3 μg/mL to 5.5 μg/mL and 0.1 μg/mL to 0.8 μg/mL under the same irradiation conditions, respectively. The IC₅₀ values of Photofrin-PDT and sinoporphyrin sodium-PDT towards human skin cells, HaCaT, were 10 μg/mL and 1.0 μg/mL, respectively. Esophagus carcinoma and hepatoma xenograft models were established to evaluate the in vivo antineoplastic efficacy. A control group, Photofrin-PDT group (20 mg/kg) and sinoporphyrin sodium group at three doses, 0.5 mg/kg, 1 mg/kg and 2 mg/kg, were set. Mice were injected with photosensitizers 24 h before 60 J 630 nm laser irradiation. The tumor weight inhibition ratio of 2 mg/kg sinoporphyrin sodium-PDT reached approximately 90%. Besides, the tumor growths were significantly slowed down by 2 mg/kg sinoporphyrin sodium-PDT, which was equivalent to 20 mg/kg Photofrin-PDT. In sum, sinoporphyrin sodium-PDT showed great anticancer efficacy and with a smaller dose compared with Photofrin. Further investigations are warranted.

Novel applications of diagnostic X-rays in activating a clinical photodynamic drug: Photofrin II through X-ray induced visible luminescence from "rare-earth" formulated particles

INTRODUCTION

In this communication we report on a novel non-invasive methodology in utilizing "soft" energy diagnostic X-rays to indirectly activate a photo-agent utilized in photodynamic therapy (PDT): Photofrin II (Photo II) through X-ray induced luminescence from Gadolinium Oxysulfide (20 micron dimension) particles doped with Terbium: Gd<formula>_{2}</formula>O<formula>_{2}</formula>S:Tb. Photodynamic agents such as Photo II utilized in PDT possess a remarkable property to become preferentially retained within the tumor's micro-environment. Upon the photo-agent's activation through (visible light) photon absorption, the agents exert their cellular cytotoxicity through type I and type II pathways through extensive generation of reactive oxygen species (ROS); namely, singlet oxygen <formula>^{1}</formula>O<formula>_{2}</formula>, superoxide anion O<formula>_{2}^{-}</formula>, and hydrogen peroxide H<formula>_{2}</formula>O<formula>_{2}</formula>, within the intra-tumoral environment. Unfortunately, due to shallow visible light penetration depth (∼ 2 mm to 5 mm) in tissues, the current PDT strategy has largely been restricted to the treatment of surface tumors, such as the melanomas. Additional invasive strategies through optical fibers are currently utilized in getting the visible light into the intended deep seated targets within the body for PDT.

METHODS

X-ray induced visible luminescence from Gd<formula>_{2}</formula>O<formula>_{2}</formula>S:Tb particles were spectroscopically characterized, and the potential in-vitro cellular cytotoxicity of Gd<formula>_{2}</formula>O<formula>_{2}</formula>S:Tb particles on human glioblastoma cells (due to 48 Hrs Gd<formula>_{2}</formula>O<formula>_{2}</formula>S:Tb particle exposure) was screened through the MTS cellular metabolic assay. In-vitro human glioblastoma cellular exposures in presence of Photo II with Gd<formula>_{2}</formula>O<formula>_{2}</formula>S:Tb particles were performed in the dark in sterile 96 well tissue culture plates, and the corresponding changes in the metabolic activities of the glioblastoma due to 15 minutes of (diagnostic energy) X-ray exposure was determined 48 Hrs after treatment through the MTS assay.

RESULTS

Severe suppression (> 90% relative to controls) in the cellular metabolic activity of human glioblastoma was measured due to the treatment of clinically relevant concentrations of 20 μg/ml Photo II, with Gd<formula>_{2}</formula>O<formula>_{2}</formula>S:Tb particles, and (120 kVp) diagnostic X-rays. Taken together, the in-vitro findings herein provide the basis for future studies in determining the safety and efficacy of this non-invasive X-ray induced luminescence strategy in activating photo-agent in deep seated tumors.

Sonodynamic therapy of cancer using novel sonosensitizers

Sonodynamic therapy (SDT) of cancer is based on preferential uptake and/or retention of a sonosensitizing drug (sonosensitizer) in tumor tissues and subsequent activation of the drug by ultrasound irradiation. Ultrasound can penetrate deeply into tissues and can be focused into a small region of a tumor to activate a sonosensitizer. This is a unique advantage in the non-invasive treatment of nonsuperficial tumors when compared to laser light used for photodynamic therapy. Recently, it has been found that photochemically active porphyrins also show significant antitumor effects when activated with ultrasound. The mechanism of sonodynamic action has been suggested to involve photoexcitation of the sensitizer by sonoluminescent light, with subsequent formation of singlet oxygen. This mini-review provides a brief overview of the following four sonosensitizers useful in SDT: i) a homogeneous complex of oligomers of hematoporphyrin, Photofrin II; ii) a gallium porphyrin complex, ATX-70; iii) a hydrophilic chlorin derivative, A7X-S10, and iv) a novel porphyrin derivative devoid of photosensitivity, DCPH-P-Na (I).

[Early diagnosis of bladder cancer by special fluorescence spectrum: an in vitro experiment]

OBJECTIVE

To investigate the value of special fluorescence spectrum in the early diagnosis of bladder cancer.

METHODS

Hematoporphyrin monomethyl ether (HMME) of the concentrations of 10, 100, and 200 microg/ml, as photosensitizer, was added into the sample vessels of bladder cancer tissue to be incubated for 1 - 3 h. A detecting system consisting of solid state ultraviolet laser with the wavelength of 355 nm was used to measure the fluorescence spectrum.

RESULTS

The laser-induced auto-fluorescence (LIAF) of the bladder cancer tissue had characteristic double peaks at 445 - 490 nm. There was a remarkable characteristic peak, drug peak, located at 628.25 nm in the laser-induced drug-fluorescence (LIDF) of the bladder cancer tissue soaked by HMME.

CONCLUSION

Photosentisizer raise the sensitivity and specificity of fluorescence spectrum in diagnosis of bladder cancer. Stable, and with high strength and visible drug peak, the LIDF is may help improve the early diagnosis of bladder cancer.

Ascorbate reacts with singlet oxygen to produce hydrogen peroxide

Singlet oxygen is a highly reactive electrophilic species that reacts rapidly with electron-rich moieties, such as the double bonds of lipids, thiols, and ascorbate (AscH-). The reaction of ascorbate with singlet oxygen is rapid (k = 3 x 10(8) M(-1) s(-1)). Here we have investigated the stoichiometry of this reaction. Using electrodes to make simultaneous, real-time measurements of oxygen and hydrogen peroxide concentrations, we have investigated the products of this reaction. We have demonstrated that hydrogen peroxide is a product of this reaction. The stoichiometry for the reactants of the reaction (1 1O2 + 1AscH--->1H2O2 + 1dehydroascorbic) is 1:1. The formation of H2O2 results in a very different oxidant that has a longer lifetime and much greater diffusion distance. Thus, locally produced singlet oxygen with a half-life of 1 ns to 1 micros in a biological setting is changed to an oxidant that has a much longer lifetime and thus can diffuse to distant targets to initiate biological oxidations.

Using white light during photodynamic therapy: visualization only or treatment?

BACKGROUND

Photodynamic therapy (PDT) involves selective uptake and retention of a photosensitizer in a tumor, followed by irradiation with light (usually a 630 nm diode laser), initiating tumor necrosis through formation of oxidized products or singlet oxygen. Successful PDT of early cancers of the esophagus and of Barrett's esophagus with severe dysplasia has been reported. However, side effects (edema, stricture, etc.) and treatment failure have been observed. This study aims to evaluate the possible photodynamic effect induced by illumination from the endoscope on the PDT effect, since a photon emitted to see the lesion can potentially be a photon to treat it!

MATERIALS AND METHODS

Two fiber endoscopes (Olympus GIFPQ20 and Pentax FG34X) and one videoendoscope (Olympus GIFQ140) were evaluated. Output power, irradiance and emission spectrum were measured. Using the molar extinction coefficient of Photofrin and optical coefficients of the esophagus, the relative photodynamic reaction yield, determined as a function of depth, was compared with that obtained with a 630 nm diode laser.

RESULTS

The irradiance at 1 and 2 cm was, respectively, 18.4 and 4.6 mW/cm (Pentax FG34X), 10.6 and 2.65 mW/cm (Olympus GIFPQ20), and 2.7 and 3.2 mW/cm (Olympus GIFQ140). The highest irradiance could lead to a relative photodynamic reaction yield at the surface of the esophagus similar to (Olympus GIFPQ20) or greater than (Pentax FG34X) that obtained using a diode laser alone.

CONCLUSIONS

Our results could explain side effects sometimes observed when performing PDT. 'Endoscopic' illumination, however, could also represent an interesting alternative to the 630 nm diode laser. When using white light, superficial efficacy of PDT could be reinforced and transmural necrosis leading to perforation or stenoses reduced, since there is less red light in depth compared with a diode laser.

Feasibility of using fluoresceinyl Cypridina luciferin analog in a novel chemiluminescence method for real-time photodynamic therapy dosimetry

Singlet oxygen ((1)O(2)) is the most important cytotoxic agent in photodynamic therapy (PDT). The feasibility of using a chemiluminescence (CL) probe, 3,7-dihydro-6-[4-(2-(N'-(5-fluoresceinyl)thioureido)ethoxy)phenyl]-2-methylimidazo{1,2-a}pyrazin-3-one sodium salt (fluoresceinyl Cypridina luciferin analog, FCLA), to monitor (1)O(2) production during PDT is evaluated in vitro. Lymphoma cells were treated with various protocols of PDT. The results show that the FCLA-CL production during PDT is linearly related to the corresponding cytotoxicity, regardless of the treatment protocol. With minimum cytotoxicity and interference to the PDT treatment outcome, the FCLA-CL system is an effective means to quantify PDT (1)O(2) production and may provide an alternative real-time dosimeter.

Modeling of a type II photofrin-mediated photodynamic therapy process in a heterogeneous tissue phantom

We present a quantitative framework to model a Type II photodynamic therapy (PDT) process in the time domain in which a set of rate equations are solved to describe molecular reactions. Calculation of steady-state light distributions using a Monte Carlo method in a heterogeneous tissue phantom model demonstrates that the photon density differs significantly in a superficial tumor of only 3 mm thickness. The time dependences of the photosensitizer, oxygen and intracellular unoxidized receptor concentrations were obtained and monotonic decreases in the concentrations of the ground-state photosensitizer and receptor were observed. By defining respective decay times, we quantitatively studied the effects of photon density, drug dose and oxygen concentration on photobleaching and cytotoxicity of a photofrin-mediated PDT process. Comparison of the dependences of the receptor decay time on photon density and drug dose at different concentrations of oxygen clearly shows an oxygen threshold under which the receptor concentration remains constant or PDT exhibits no cytotoxicity. Furthermore, the dependence of the photosensitizer and receptor decay times on the drug dose and photon density suggests the possibility of PDT improvement by maximizing cytotoxicity in a tumor with optimized light and drug doses. We also discuss the utility of this model toward the understanding of clinical PDT treatment of chest wall recurrence of breast carcinoma.

Heme oxygenase-1 protects tumor cells against photodynamic therapy-mediated cytotoxicity

Photodynamic therapy is a promising antitumor treatment modality approved for the management of both early and advanced tumors. The mechanisms of its antitumor action include generation of singlet oxygen and reactive oxygen species that directly damage tumor cells and tumor vasculature. A number of mechanisms seem to be involved in the protective responses to PDT that include activation of transcription factors, heat shock proteins, antioxidant enzymes and antiapoptotic pathways. Elucidation of these mechanisms might result in the design of more effective combination strategies to improve the antitumor efficacy of PDT. Using DNA microarray analysis to identify stress-related genes induced by Photofrin-mediated PDT in colon adenocarcinoma C-26 cells, we observed a marked induction of heme oxygenase-1 (HO-1). Induction of HO-1 with hemin or stable transfection of C-26 with a plasmid vector encoding HO-1 increased resistance of tumor cells to PDT-mediated cytotoxicity. On the other hand, zinc (II) protoporphyrin IX, an HO-1 inhibitor, markedly augmented PDT-mediated cytotoxicity towards C-26 and human ovarian carcinoma MDAH2774 cells. Neither bilirubin, biliverdin nor carbon monoxide, direct products of HO-1 catalysed heme degradation, was responsible for cytoprotection. Importantly, desferrioxamine, a potent iron chelator significantly potentiated cytotoxic effects of PDT. Altogether our results indicate that HO-1 is involved in an important protective mechanism against PDT-mediated phototoxicity and administration of HO-1 inhibitors might be an effective way to potentiate antitumor effectiveness of PDT.

The future of photodynamic therapy in oncology

The medicinal properties of light-based therapies have been appreciated for millennia. Yet, only in this century have we witnessed the birth of photodynamic therapy (PDT), which over the last few decades has emerged to prominence based on its promising results and clinical simplicity. The fundamental and distinguishing characteristics of PDT are based on the interaction of a photosensitizing agent, which, when activated by light, transfers its energy into an oxygen-dependent reaction. Clinically, this photodynamic reaction is cytotoxic and vasculotoxic. While the current age of PDT is based on oncological therapy, the future of PDT will probably show a significant expansion to non-oncological indications. This harks back to much of the original work from a century ago. Therefore, this paper will attempt to predict the future of PDT, based in part on a review of its origin.

The phototoxicity of photofrin was enhanced by PEGylated liposome in vitro

In recent years, photodynamic therapy (PDT) with a photosensitizer and laser has been given attention, especially for the treatment of superficial cancers, such as lung, gastric, bladder and cervical cancer. In this study, in order to enhance the efficacy of PDT, photofrin liposome (PF-Lip) was prepared with dimyristoylphosphatidylcholine, dimyristoylphosphatidylglycerol and cholesterol. Polyethyleneglycol modified photofrin liposome (PF-PEG-Lip) was prepared by modification of PF-Lip with monomethoxypolyethyleneglycol-2.3-dimyristoylglycerol. PF-Lip and PF-PEG-Lip entrapped with photofrin with 81.0+/-5.9 and 81.2+/-9.2%, respectively. The particle size of each liposome was 114.3+/-5.7nm (PF-Lip) and 118+/-3.5nm (PF-PEG-Lip), respectively. It was suggested that PEGylated liposomes has no effect on the trapping ratio of PF and particle size. Phototoxicity was enhanced by liposomalization, especially PEG-modification. However, PF-PEG-Lip inhibited the uptake of photofrin into tumor cells. The amount of singlet oxygen from photofrin solution (PF-sol) and each liposome was PF-PEG-Lip=PF-Lip>PF-sol. The photofrin release revel of PF-PEG-Lip was lower than that of PF-Lip. In conclusion, the phototoxicity of PF-PEG-Lip was significantly higher than that of PF-sol or PF-Lip. It is expected that formation of a fixed aqueous layer on the liposome membrane by PEGylation physically changed it into the stable state of PF-PEG-Lip.

Photodynamic effects of porphyrin and chlorin photosensitizers in human colon adenocarcinoma cells

Photodynamic therapy (PDT) is a cancer treatment involving systemic administration of a tumor-localizing photosensitizer; this, when activated by the appropriate wavelength of light, interacts with molecular oxygen to form a toxic, short-lived species known as singlet oxygen, which is thought to mediate cellular death. Photofrin, a complex mixture of porphyrin oligomers has recently received FDA approval for the photodynamic treatment of esophageal and endobronchial carcinoma, but its photodynamic and toxicity profiles are far from ideal. In the present study we evaluated a series of porphyrin-based PSs, some of which newly synthesized by our group, with the aim to identify agents with more favorable characteristics. For the most effective compounds in the porphyrin series, chlorin analogs were also synthesized; for comparison, the screening also included Photofrin. Cytotoxicity studies were performed by the MTT assay on a cultured human colon adenocarcinoma cell line (HCT116); the results indicate that the 3,4,5-trimethoxyphenyl, 3OH- and 4OH-phenyl, and the sulfonamidophenyl derivatives are significantly more potent than Photofrin. Flow cytometric studies and fluorescence microscopy indicate that in PDT-treated HCT116 cells death occurs mainly by apoptosis. In summary, novel PSs described in the present study, belonging both to the porphyrin and chlorin series, have proven more effective than Photofrin in killing colon cancer cells in vitro; extending these observation to in vivo models, particularly regarding the deeper reaching chlorin derivatives, might lead to significant advances in the development of tumor PDT.

Time-Resolved Investigations of Singlet Oxygen Luminescence in Water, in Phosphatidylcholine, and in Aqueous Suspensions of Phosphatidylcholine or HT29 Cells

Singlet oxygen was generated by energy transfer from the photoexcited sensitizer, Photofrin or 9-acetoxy-2,7,12,17-tetrakis-(beta-methoxyethyl)-porphycene (ATMPn), to molecular oxygen. Singlet oxygen was detected time-resolved by its luminescence at 1270 nm in an environment of increasing complexity, water (H2O), pure phosphatidylcholine, phosphatidylcholine in water (lipid suspensions), and aqueous suspensions of living cells. In the case of the lipid suspensions, the sensitizers accumulated in the lipids, whereas the localizations in the cells are the membranes containing phosphatidylcholine. By use of Photofrin, the measured luminescence decay times of singlet oxygen were 3.5 +/- 0.5 micros in water, 14 +/- 2 micros in lipid, 9 +/- 2 micros in aqueous suspensions of lipid droplets, and 10 +/- 3 micros in aqueous suspensions of human colonic cancer cells (HT29). The decay time in cell suspensions was much longer than in water and was comparable to the value in suspensions of phosphatidylcholine. That luminescence signal might be attributed to singlet oxygen decaying in the lipid areas of cellular membranes. The measured luminescence decay times of singlet oxygen excited by ATMPn in pure lipid and lipid suspensions were the same within the experimental error as for Photofrin. In contrast to experiments with Photofrin, the decay time in aqueous suspension of HT29 cells was 6 +/- 2 micros when using ATMPn.

Hypocrellin derivative with improvements of red absorption and active oxygen species generation

A novel diamino-substituted hypocrellin derived from hypocrellin B (HB) was synthesized by a mild method. The red absorption of the resulting product was significantly enhanced relative to the parent hypocrellins and any other hypocrellin derivatives, and the active oxygen species generating abilities were enhanced distinctly, which will remarkably improve its photodynamic therapy effectiveness.

Photodynamic therapy of head and neck tumors and non-tumor like disorders

In conclusion, we would like to emphasize that photodynamic therapy can be used as a convenient and promising tool in the treatment of various malignancies in the head and neck area. It has to be stressed that PDT is still less effective in the treatment of more advanced cases of head and neck cancer. As the method of treatment which improves the quality of life, its usefulness can be considered as well as palliative treatment of non-operative cases. Although the method is not free of several side effects, such skin phototoxicity, burning, slight pain and edema in the irradiated location. All these side effects are transient and usually they disappear within 24 hours. The photodynamic treatment always results in excellent cosmetic effects without scarring or marring which are usually encountered after routine surgical operation.

Measurement of fluorophore concentrations and fluorescence quantum yield in tissue-simulating phantoms using three diffusion models of steady-state spatially resolved fluorescence

Steady-state diffusion theory models of fluorescence in tissue have been investigated for recovering fluorophore concentrations and fluorescence quantum yield. Spatially resolved fluorescence, excitation and emission reflectance Carlo simulations, and measured using a multi-fibre probe on tissue-simulating phantoms containing either aluminium phthalocyanine tetrasulfonate (AlPcS4), Photofrin meso-tetra-(4-sulfonatophenyl)-porphine dihydrochloride The accuracy of the fluorophore concentration and fluorescence quantum yield recovered by three different models of spatially resolved fluorescence were compared. The models were based on: (a) weighted difference of the excitation and emission reflectance, (b) fluorescence due to a point excitation source or (c) fluorescence due to a pencil beam excitation source. When literature values for the fluorescence quantum yield were used for each of the fluorophores, the fluorophore absorption coefficient (and hence concentration) at the excitation wavelength (mu(a,x,f)) was recovered with a root-mean-square accuracy of 11.4% using the point source model of fluorescence and 8.0% using the more complicated pencil beam excitation model. The accuracy was calculated over a broad range of optical properties and fluorophore concentrations. The weighted difference of reflectance model performed poorly, with a root-mean-square error in concentration of about 50%. Monte Carlo simulations suggest that there are some situations where the weighted difference of reflectance is as accurate as the other two models, although this was not confirmed experimentally. Estimates of the fluorescence quantum yield in multiple scattering media were also made by determining mu(a,x,f) independently from the fitted absorption spectrum and applying the various diffusion theory models. The fluorescence quantum yields for AlPcS4 and TPPS4 were calculated to be 0.59 +/- 0.03 and 0.121 +/- 0.001 respectively using the point source model, and 0.63 +/- 0.03 and 0.129 +/- 0.002 using the pencil beam excitation model. These results are consistent with published values.

Photodynamic action of some sensitizers by photooxidation of luminol

We report the development of a novel simple experimental method which allows the comparison of new photosensitizers based on their production of reactive oxygen species. A high-performance liquid chromatography (HPLC) assay permits the monitoring of several substances (sensitizer, reactant and oxidized end product) simultaneously on a single chromatogram. Photoreactions were monitored throughout their course by the HPLC assay surveying the sensitizers' efficiency of singlet oxygen production by the oxidative decomposition of luminol. Several photosensitizers were tested: Rose Bengal, Methylene Blue, Protoporphyrin IX, Photosan III, Photofrin, Hypericin and Pseudohypericin. Additionally, photoreactions were monitored by a standard pO(2) detection system. The measurements of the two detection methods were strongly correlated. Rose Bengal proved to be the most efficient photosensitizer, clearly decreasing the luminol concentration and causing a corresponding increase in aminophthalic acid. Our experiments show that when factors necessary for photochemical reactions are absent or are blocked (antioxidants), no reaction can be detected.

Photodynamic effect of deuteroporphyrin IX and hematoporphyrin derivatives on single neuron

The photodynamic effects of 6 new deuteroporphyrin IX derivatives with different amphiphilicity and lipophilicity, as well as effects of known hematoporphyrin derivatives Photofrin II and Photoheme on isolated crayfish mechanoreceptor neurons were studied. After 30 min photosensitization, neurons were irradiated with He-Ne laser (632.8 nm, 0.3 W/cm(2)), and changes in their firing frequency were recorded. Neuron firing was shown to be very sensitive to photodynamic effect of the studied deuteroporphyrin IX derivatives causing irreversible firing abolition at pikomolar concentrations while Photoheme and Photofrin II were effective in the nanomolar range. The most effective sensitizers were 4-(1-methyl-3-hydroxybutyl)- and 4-(1-methyl-2-acetyl-3-oxobutyl)-deuteroporphyrins. Extinction and amphiphilicity were shown to be the most important properties determining photodynamic efficiency of the studied photosensitizers.

Are porphyrin mixtures favorable photodynamic anticancer drugs? A model study with combinatorial libraries of tetraphenylporphyrins

Reported here is the preparation of tetraphenylporphyrin libraries via efficient combinatorial solution-phase syntheses, their purification, and preliminary results from a bioorganic study on their uptake in liposome membranes. Libraries with up to 666 components were prepared with substituents including Br, CF3, Cl, CN, CO2Me, Et, F, OAc, and Ph. Further, a first example for the synthesis of more diverse libraries via a "latent libraries" approach is presented. This involves masking polar groups with lipophilic protecting groups. After purification of the latent library, the masking protecting groups are removed in a quantitative reaction that produces the library compounds as the only non-volatile components. Libraries were characterized by laser desorption time-of-flight mass spectrometry, NMR, and UV-vis spectroscopy. In vitro uptake into membranes of small sonicated liposomes was measured, both in terms of total porphyrin incorporation and in terms of structure-incorporation relationships. The latter were determined from isotopically-resolved laser-desorption mass spectra under conditions that yield quantitative results. Smaller libraries showed increased uptake of porphyrins bearing OH and CF3 substituents and lower uptake of ester-, alkyl-, and halide-bearing porphyrins. This structure-dependent selectivity disappears for larger libraries, however, where uniformly high uptake is observed, i.e., at a constant lipid:porphyrin ratio the total porphyrin incorporation is higher for libraries than for single compounds of similar polarity. We propose that the decreased concentration of individual compounds in large libraries is responsible for this effect. Membrane incorporation has previously been shown to correlate with photodynamic activity in vitro and in vivo.16 Therefore, these results may help to explain why photodynamic therapy of tumors, a modern anti-cancer treatment modality, is successfully performed with a complex mixture of porphyrins.

Comparative mass spectrometric analyses of Photofrin oligomers by fast atom bombardment mass spectrometry, UV and IR matrix-assisted laser desorption/ionization mass spectrometry, electrospray ionization mass spectrometry and laser desorption/jet-cooling photoionization mass spectrometry

Photofrin (porfimer sodium) is a porphyrin derivative used in the treatment of a variety of cancers by photodynamic therapy. This oligomer complex and a variety of porphyrin monomers, dimers and trimers were analyzed with five different mass spectral ionization techniques: fast atom bombardment, UV and IR matrix-assisted laser desorption/ionization, electrospray ionization, and laser desorption/jet-cooling photoionization. All five approaches resulted in very similar oligomer distributions with an average oligomer length of 2.7 +/- 0.1 porphyrin units. In addition to the Photofrin analysis, this study provides a side-by-side comparison of the spectra for the five different mass spectrometric techniques.

Photodynamic therapy: an update

Photodynamic therapy (PDT) is a promising local treatment modality based on the selective accumulation of a photosensitizer in malignant tissues and the subsequent irradiation with laser light. Photodynamic therapy of malignant tumors includes biological, photochemical and photophysical processes. These processes involve: (a) absorption of photosensitizing agent; (b) selective retention of the photosensitizer in tumors and (c) irradiation of sensitized tumor by laser radiation. This report provides a review of photosensitizers, photochemistry, subcellular targets, side effects and laser involved in photodynamic therapy. In addition, gradual increase in knowledge related to in vitro and in vivo mechanisms of action of PDT, as well as some clinical applications of photodynamic therapy are presented.

Cellular accumulation and biological activity of hematoporphyrin derivative(L) in comparison with photofrin II

Hematoporphyrin derivative, a drug used in the photodynamic therapy of solid tumours was synthesized in the laboratory and was called Hpd(L). Physico-chemical and biological properties of this drug have been compared with Photofrin II, the commercially available drug. Both Hpd(L) and Photofrin II possess similar properties qualitatively. Quantitatively, Hpd(L) was half as active as Photofrin II in its efficacy in causing photodynamic cytotoxicity or in the optical densities at the absorption peaks. These differences could be due to the differences in the compositions. Hpd(L) is a non-purified complex mixture of a number of porphyrin derivatives whereas Photofrin II is a relatively purer compound consisting of di- and tri-hematoporphyrins linked through ether or ester bonds. In vitro cellular uptake and retention of these drugs has been found to be a passive process not involving energy expenditure. pH and temperature of the incubation media have been found to profoundly influence these processes, while a complex relation seems to exist between physiological state of a cell and accumulation of these photosensitizers.

[Porfimer sodium (Photofrin-II)]

Porfimer sodium (Photofrin II) is a photosensitizer which distributes selectively to tumor tissues, and causes tumor cell death by combination with light irradiation. Photodynamic therapy (PDT) by combination of porfimer sodium and laser was developed as a new cancer therapy. Tumor selectivity of porfimer sodium are based on the following reasons; 1) high affinity for lipoprotein, especially, low density lipoprotein (LDL), 2) elevation of LDL receptor activity in cancer tissue, and 3) lack or imcompleteness of lymphatic system in cancer tissue. Porfimer sodium is activated by laser irradiation at 630 nm, which can reacts with tissue oxygen to produce highly reactive excited siglet oxygen (1O2). This highly reactive molecule is subsequently capable of killing tumor cells through oxidation of cellular component like mitochondrial enzymes. In addition, this highly reactive intermediate causes destruction of the tumor capillaries, which accelerates tumor cell death. The growth suppression or lethal damage to tumor cells by PDT of porfimer sodium and excimer dye laser were observed in experimental tumor models. In human clinical trials, the rates of complete response (CR) for roentgenographically occult lung cancer, stage I lung cancer, superficial esophageal cancer, superficial gastric cancer and carcinoma in situ or dysplasia of the cervix were 84.8%, 50.0%, 90.0%, 87.5% and 94.4%, respectively. The major side effects were cutaneous symptoms e.g. photosensitivity, pigmentation, increasing GOT, GPT but these symptoms were not severe. PDT using porfimer sodium and excimer dye laser must be clinically useful for the treatment of inoperable early cancer or conservation of organ functions.

Dye-sensitized destabilization of liposomes bearing photooxidizable lipid head groups

Liposomes were prepared from mixtures of dipalmitoyl-L-alpha-phosphatidylcholine and up to 40% mol:mol of N-stearoyl-L-histidine (NSH) in the presence of the hydrophobic sensitizer DHE. In the dark such liposomes are stable and retain entrapped salts. On photolysis with visible light, liposomes leak trapped ions at NSH concentrations greater than 10% mol:mol. Up to 15% mol:mol NSH concentration leakage is seen only during the illumination period, whereas at higher concentration the liposomes continue to leak contents after illumination and fuse to form larger structures. Photolysis of the liposomes is accompanied by oxygen uptake in proportion to the NSH concentration within the bilayer. Photocontrol of liposome permeability through oxidation of membrane additives such as NSH offers a potential means for controlled drug delivery and might be useful as an adjunct to photodynamic therapy.

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.