Successful cutaneous delivery of the photosensitizer silicon phthalocyanine 4 for photodynamic therapy.

BACKGROUND: Photodynamic therapy (PDT) has been shown to be effective in the treatment of malignancies of a variety of organ systems, including the lungs, bladder, gastrointestinal tract and skin. Cutaneous lesions serve as ideal targets of PDT because of the accessibility of the skin to light. To achieve optimum results, the photosensitizer must be delivered effectively into the target layers of the skin within a practical timeframe, via noninvasive methods. AIM: To determine whether topical application of a second-generation photosensitizer, silicon phthalocyanine (Pc) 4 [SiPc(OSi(CH3)2 (CH2)3 N(CH3)2)(OH)], results in effective penetration of the skin barrier. METHODS: Penetration of Pc 4 was evaluated using standard Franz-type vertical diffusion cell experiments on surrogate materials (silicone membranes) and laser-scanning confocal microscopy of normal skin biopsy samples from human volunteers. RESULTS: The Franz diffusion data indicate that Pc 4 formulated in an ethanol/propylene glycol solution (70/30%, v/v) can penetrate the membrane at a flux that is appreciable and relatively invariant. Using the same formulation, Pc 4 uptake could be detected in human skin via laser-scanning confocal microscopy. CONCLUSION: After topical application, Pc 4 is absorbed into the epidermis in as little as 1 h, and the absorption increased with increasing time and dose. Pc 4 can be effectively delivered into human skin via topical application. The data also suggest that the degree of penetration is time- and dose-dependent.

Photodynamic therapy of ocular melanoma with bis silicon 2,3-naphthalocyanine in a rabbit model.

PURPOSE: To investigate bis (tri-n-hexylsiloxy) silicon 2,3-naphthalocyanine (SINc; 0.5 mg/kg) for photodynamic therapy of an experimental ocular melanoma in pigmented rabbits. METHODS: SINc was dissolved in canola oil by heating, emulsified with Tween 80, and administered by ear vein. Pharmacokinetics were studied in frozen tumor sections by fluorescence microscopy using a charge coupled device, camera-based, low-light detection system with digital image processing at 1 and 24 hours. A Ti:sapphire laser and a microlens were used to deliver the light (770 nm; 40 mW/cm2; 20 J/cm2). A control rabbit received light without SINc. RESULTS: Localization studies of SINc showed intravascular distribution shifting to a tumor stromal and perivascular distribution 24 hours after treatment. Tissue thermal damage after irradiation was minimal in the control. Exudative retinal detachments were not observed. Tumor destruction was observed, with sharp demarcation to a depth of 3.5 mm. CONCLUSIONS: Tumor light penetration was good at 770 nm, and thermal effects from the exciting light alone were minimal. Photodynamic therapy with SINc resulted in localized tumor destruction reflecting the light beam path without damage to adjacent tissue or intraocular complications.

Effect of the delivery system on the biodistribution of Ge(IV) octabutoxy-phthalocyanines in tumour-bearing mice.

The pharmacokinetic properties of the Ge(IV)-octabutoxy-phthalocyanines (GePc) with two axially ligated triethylsiloxy (GePcEt) or trihexyl-siloxy (GePcHex) chains were studied in BALB/C mice bearing a transplanted MS-2 fibrosarcoma. The GePcs were delivered to mice after incorporation into unilamellar liposomes of dipalmitoyl phosphatidylcholine (DPPC) or in an emulsion of Cremophor-EL. The Cremophor delivered GePcs were cleared from the blood circulation at a much slower rate than the liposome-delivered GePcs. At the same time, Cremophor induced a slower and reduced uptake of the GePcs in the liver and spleen while it greatly enhanced the uptake in the tumour as compared to liposomes. Maximum tumour uptake was observed at 24 h post-injection and was equivalent to 0.67 and 0.50 nmol/g, respectively, for the Cremophor delivered GePcHex and GePcEt. The corresponding values for the liposome-delivered drugs were approximately one fourth of that observed with Cremophor.

Si(IV)-naphthalocyanine: modulation of its pharmacokinetic properties through the use of hydrophilic axial ligands.

A water-soluble derivative of the highly hydrophobic molecule Si(IV)-naphthalocyanine was synthesized by the addition of two polyethyleneglycol ligands in axial positions to the centrally coordinated Si(IV) ion. The compound can be intravenously injected in homogeneous aqueous solution, where it is largely aggregated and remains mostly in an unbound state. While the naphthalocyanine is accumulated in significant amounts by an intramuscularly transplanted MS-2 fibrosarcoma in Balb/c mice, the dye shows little tumour selectivity and essentially no phototherapeutic activity. The situation is not improved by association of the naphthalocyanine with dipalmitoyl-phosphatidylcholine liposomes, probably owing to a lack of incorporation of the bulky dye molecule into the phospholipid bilayer.

New phthalocyanine photosensitizers for photodynamic therapy.

Six new aluminum and silicon phthalocyanines have been synthesized and their photocytotoxicity toward V79 cells has been studied. The compounds that have been prepared are: A1PcOSi(CH3)2(CH2)3N(CH3)2, I; A1Pc-OSi(CH3)2(CH2)3N(CH3)3+I-, II; CH3SiPcOSi(CH3)2(CH2)3N(CH3)2, III; HOSiPcOSi(CH3)2(CH2)3N(CH3)2, IV; HOSiPcOSi(CH3)2(CH2)3N(CH3)3+I-, V; and SiPc[OSi(CH3)2(CH2)3N(CH3)3+I-]2, VI. Relative growth delay values for compounds I-VI and relative cytotoxicity values for compounds I, II, IV, V and VI have been determined. Compounds I and II have been shown to be comparable in photocytotoxicity to what is presumed to be A1PcOH.xH2O, and compound IV has been shown to have greater activity. The classes of compounds to which these six compounds belong appear to have potential for photodynamic therapy.

The effect of irradiance on virus sterilization and photodynamic damage in red blood cells sensitized by phthalocyanines.

Phthalocyanines are being studied as photosensitizers for virus sterilization of red blood cells (RBC). During optimization of the reaction conditions, we observed a marked effect of the irradiance on production of RBC damage. Using a broad-band light source (600-700 nm) between 5 and 80 mW/cm2, there was an inverse relationship between irradiance and rate of photohemolysis. This effect was observed with aluminum sulfonated phthalocyanine (AlPcSn) and cationic silicon (HOSiPc-OSi[CH3]2[CH2]3N+[CH3]3I- phthalocyanine (Pc5) photosensitizers. The same effect occurred when the reduction of RBC negative surface charges was used as an endpoint. Under the same treatment conditions, vesicular stomatitis virus inactivation rate was unaffected by changes in the irradiance. Reduction in oxygen availability for the photochemical reaction at high irradiance could explain the effect. However, theoretical estimates suggest that oxygen depletion is minimal under our conditions. In addition, because the rate of photohemolysis at 80 mW/cm2 was not increased when irradiations were carried out under an oxygen atmosphere this seems unlikely. Likewise, formation of singlet oxygen dimoles at high irradiances does not appear to be involved because the effect was unchanged when light exposure was in D2O. While there is no ready explanation for this irradiance effect, it could be used to increase the safety margin of RBC virucidal treatment by employing exposure at high irradiance, thus minimizing the damage to RBC.

Two new sterically hindered phthalocyanines: synthetic and photodynamic aspects.

The synthesis and the properties of 1,4-dibutoxy-2,3-dicyanotriptycene, of a metal-free tetradibenzobarrelenooctabutoxyphthalocyanine, and of the corresponding zinc phthalocyanine are described. The two phthalocyanines do not aggregate when dissolved in benzene at concentrations up to 450 microM. For the metal-free and the zinc compounds, the red band maxima are at 736 and 757 nm, the triplet maxima are at 590 and 605 nm, the triplet state lifetimes are 58 and 177 microseconds, and the protoporphyrin-IX dimethyl ester-to-compound bimolecular rate constants for triplet energy transfer are 2.61 x 10(8) and 1.47 x 10(8) M-1 s-1. Triplet energy transfer from the metal-free compound to O2 is endoergonic by 1.0 kcal mol-1. The potential of the zinc compound for photodynamic therapy is touched upon.

Photodynamic effects of new silicon phthalocyanines: in vitro studies utilizing rat hepatic microsomes and human erythrocyte ghosts as model membrane sources.

Photodynamic therapy (PDT) of cancer is a modality that relies upon the irradiation of tumors with visible light following selective uptake of a photosensitizer by the tumor tissue. There is considerable emphasis to define new photosensitizers suitable for PDT of cancer. In this study we evaluated six phthalocyanines (Pc) for their photodynamic effects utilizing rat hepatic microsomes and human erythrocyte ghosts as model membrane sources. Of the newly synthesized Pc, two showed significant destruction of cytochrome P-450 and monooxygenase activities, and enhancement of lipid peroxidation, when added to microsomal suspension followed by irradiation with approximately 675 nm light. These two Pc named SiPc IV (HOSiPcOSi[CH3]2[CH2]3N[CH3]2) and SiPc V (HOSiPc-OSi[CH3]2[CH2]3N[CH3]3+I-) showed dose-dependent photodestruction of cytochrome P-450 and monooxygenase activities in liver microsomes, and photoenhancement of lipid peroxidation, lipid hydroperoxide formation and lipid fluorescence in microsomes and erythrocyte ghosts. Compared to chloroaluminum phthalocyanine tetrasulfonate, SiPc IV and SiPc V produced far more pronounced photodynamic effects. Sodium azide, histidine, and 2,5-dimethylfuran, the quenchers of singlet oxygen, afforded highly significant protection against SiPc IV- and SiPc V-mediated photodynamic effects. However, to a lesser extent, the quenchers of superoxide anion, hydrogen peroxide and hydroxyl radical also showed some protective effects. These results suggest that SiPc IV and SiPc V may be promising photosensitizers for the PDT of cancer.

Biodistribution and virus inactivation efficacy of a silicon phthalocyanine in red blood cell concentrates as a function of delivery vehicle.

The silicon phthalocyanine, HOSiPcOSi(CH3)2(CH2)3N(CH3)2 (Pc 4), is a new photosensitizer that can inactivate lipid-enveloped viruses in red blood cell concentrates (RBCC) upon exposure to red light. Because Pc 4 is insoluble in water, it was delivered either as an emulsion in saline and cremophor EL (CRM) or as a solution in dimethyl sulfoxide (DMSO). In RBCC, Pc 4 added in either vehicle distributed between the plasma and red blood cells (RBC) in a ratio of 4:6, similar to the ratio of these components in RBCC 3:7 (i.e. a hematocrit of 70%). Light exposure did not affect this distribution and caused only marginal degradation of Pc 4 at a light dose that inactivates > 5 log10 vesicular stomatitis virus (VSV). Among human plasma proteins, Pc 4 bound mainly (about 70%) to lipoproteins and to a lesser extent to albumin and lower molecular weight proteins when delivered in DMSO. When delivered in CRM, distribution between lipoproteins and albumin became more even. Among the lipoproteins Pc 4 bound almost exclusively to very low-density lipoproteins (VLDL) when delivered in DMSO and to both VLDL and low-density lipoproteins when added in CRM. The rate of VSV inactivation was independent of the delivery vehicle but there was less RBC damage, as measured by hemolysis during storage, when Pc 4 was added in CRM. These results indicate that using CRM as emulsifier can enhance the specificity of Pc 4-induced photochemical decontamination of RBCC for transfusion.

Structure-activity and mechanism studies on silicon phthalocyanines with Plasmodium falciparum in the dark and under red light.

Syntheses for the new photosensitizers HOSiPcOSi(CH3)2(CH2)3N(CH1)1 or 3(CH3)2, Pc 34 and Pc 25, have been developed and the order of activity of these photosensitizers and the previously reported photosensitizer Pc 4, HOSiPcOSi(CH3)2(CH2)3N(CH3)2, in the dark and with broad-band red light toward Plasmodium falciparum in red blood cell (RBC) suspensions has been studied. The order of activity has been found to be Pc 4 > Pc 34 > Pc 25. Thus, the activity of the photosensitizers under both sets of conditions is inversely proportional to the length of their terminal amino alkyl chains. The 50% inhibition dye concentration (IC50) in the dark for the parasites in RBC suspension with Pc 4 is 24 nM and the dye concentration and light fluence that yield > or = 3 log10 of parasite inactivation with Pc 4 are 2 microM and 3 J/cm2, respectively. The synthesis of DNA and proteins by the parasites in culture was strongly inhibited by Pc 4 in the dark while parasite lactate dehydrogenase (pLDH) activity was unaffected. With Pc 4 and light, DNA and protein synthesis of the parasites in culture was strongly inhibited, pLDH activity of the parasites was moderately inhibited and ribosome density of the parasite cells was reduced. Gel electrophoresis studies showed that synthesis of all parasite proteins was inhibited to a similar extent. These results suggest that Pc 4 both in the dark and with light inactivates the cells by disturbing their machinery for the synthesis of not just one but a whole series of proteins. It is concluded that Pc 4 and light may be able to serve as a practical sterilization combination not only for HIV and other viruses but also for malaria parasites in RBC concentrates, and that Pc 4 by itself may have potential as a chemotherapeutic agent toward malaria.

Treatment of malignant melanoma by high-peak-power 1064 nm irradiation followed by photodynamic therapy.

Irradiation of B16 pigmented melanoma subcutaneously transplanted in C57 mice with a single 650 mJ pulse (10 ns) of 1064 nm light from a Q-switched Nd: YAG laser caused instantaneous bleaching of the pigmented tissue. Visual and histological examination of the resulting gray-colored tumor revealed the breakdown of melanosomes with no detectable alteration of the normal and tumor-overlying skin. Histological examination of the irradiated tumor showed some degree of vascular damage; the depth of the photodamage was not affected by the successive delivery of three consecutive light pulses. The bleached tumor grew at a modestly slower rate but the high-peak-power (HPP) laser treatment did not affect the tumor concentration of a photodynamic sensitizer Si(i.v.)-naphthalocyanine (isoBO-SiNc) intravenously injected 24 h before Nd:YAG irradiation. Treatment of the B16 pigmented melanoma by photodynamic therapy (PDT: 1 mg/kg isoBO-SiNc, 300 mW/cm2, 520 J/cm2) from a 774 nm diode laser immediately after the 1064 nm irradiation resulted in a 16 day delay of tumor regrowth, which was markedly longer than the delay (ca 6 days) obtained after PDT under identical conditions without the preirradiation. Thus, pretreatment of pigmented tumors with HPP 1064 nm light appears to enhance their susceptibility to conventional PDT. The tumor response was further enhanced by repeating the combined HPP/PDT treatment at an interval of 10 days (regrowth delay: 27 days), as well as by applying hyperthermia immediately after HPP/PDT (regrowth delay: ca 34 days).

Effect of delivery system on the pharmacokinetics and tissue distribution of bis(di-isobutyl octadecylsiloxy)silicon 2,3-naphthalocyanine (isoBOSINC), a photosensitizer for tumor therapy.

Bis(di-isobutyl octadecylsiloxy)silicon 2,3-naphthalocyanine (isoBOSINC) is a representative of a group of naphthalocyanine derivatives with spectral and photophysical properties that make them attractive candidates for photodynamic therapy (PDT). Tissue distributions were studied in tumor-bearing rats as a function of delivery system and time following administration. The tumor model was an N-(4-[5-nitro-2-furyl]-2-thiazolyl) formamide (FANFT)-induced urothelial cell carcinoma transplanted into one hind leg of male Fischer 344 rats; isoBOSINC was delivered to the rats by intravenous injection of 0.50 mg/kg of body weight as a suspension either in 10% Tween 80 in saline (Tween) or 10% (Cremophor EL + propylene glycol) in saline (Cremophor). The isoBOSINC was isolated from several tissues and organs, as well as tumors and peritumoral muscles and skin. Quantitation was by a high-performance liquid chromatographic technique with detection that utilizes the native fluorescence of the naphthalocyanine derivative. Independent of the delivery system, the dye was retained in tumors at higher concentrations than in normal tissues, except for spleen and liver. The isoBOSINC retention in tumors was high and was vehicle dependent. For Tween, the maximal ratio of dye in tumor versus peritumoral muscle occurred 12 h after injection; for Cremophor, the maximal ratio occurred later, 336 h postinjection. When the drug was delivered in Tween, isoBOSINC in serum showed two compartment kinetics: half-lives of about 2 and 11 h were found for the distribution and the elimination phases, respectively. When Cremophor was the vehicle, the elimination half-life was about 20 h, and one compartment kinetics was observed. The latter findings may explain the generally higher levels of the dye attained by the tissues at later times with Cremophor as the vehicle. An interesting exception was that after 7 and 14 days postinjection in Tween, the levels of dye found in testes were six- to seven-fold higher than those found after Cremophor delivery. Levels of dye were very low or not detectable in the brain. Optimal parameters for PDT of tumors with this novel photosensitizer are clearly time- and vehicle-dependent, and future PDT studies will need to incorporate these modulators.

Effect of photosensitizer delivery system and irradiation parameters on the efficiency of photodynamic therapy of B16 pigmented melanoma in mice.

Previous studies (Biolo et al., Photochem. Photobiol. 59, 362-365, 1994) showed that liposome-delivered Si(IV)-naphthalocyanine (SiNc) photosensitizes B16 pigmented melanoma subcutaneously transplanted in C57 mice to the action of 776 nm light. However, the efficacy of the phototreatment was limited by a lack of selectivity of tumor targeting by SiNc as well as by incomplete necrosis of the neoplastic mass. The present investigations show that the use of a different delivery system (Cremophor emulsion vs liposomes of dipalmitoylphosphatidylcholine) causes no significant increase in the selectivity of tumor targeting for three injected doses of SiNc (0.5, 1, 2 mg/kg). However, upon 776 nm light irradiation (300 mW/cm2; 520 J/cm2), the delay in the rate of tumor growth was maximal (7-8 days) for the highest naphthalocyanine dose. On the other hand, a remarkable improvement in the tumor response was obtained by inducing an intratumoral temperature increase to 44 degrees C immediately after PDT. The thermal effect appeared to be due to photoexcitation of melanin by 776 nm light (550 mW/cm2; 520 J/cm2) and subsequent partial conversion of absorbed energy into heat.

Photoproperties of alkoxy-substituted phthalocyanines with deep-red optical absorbance.

Triplet-state properties of 1,4,8,11,15,18,22,25-octa-n-butoxyphthalocyanine and its zinc derivative were determined for the first time. The T1 state of the metal-free phthalocyanine was characterized by a short lifetime (tau T = 17 microseconds) and low quantum yield (phi T = 0.095), and quenching of the triplet by O2 occurred with a bimolecular rate constant (kT sigma = 1.3 x 10(8) M-1 s-1) that is indicative of an endogonic reaction. The zinc complex (ZnPc(OBu)8) was markedly better as a triplet photosensitizer with respect to both tau T (60 microseconds) and phi T (0.5). Quenching by O2 produced singlet oxygen with nearly 100% efficiency, and kT sigma (1.7 x 10(9) M-1s-1) was close to the spin-statistical diffusion-controlled limit. Phosphorescence measurements showed the energy of the T1 state of ZnPc(OBu)8 to be 100 kJ/mol, which is 6 kJ/mol above the 1 delta g state of O2. These photoproperties, together with Q-band absorption maxima in the mid-700 nm range indicate that metal-centered 1,4,8,11,15,18,22,25-octaalkoxyphthalocyanines have excellent potential as sensitizers in photodynamic therapy.

Pharmacokinetic and tissue distribution studies of the photosensitizer bis(di-isobutyl octadecylsiloxy)silicon 2,3-naphthalocyanine (isoBOSINC) in normal and tumor-bearing rats.

Bis(di-isobutyl octadecylsiloxy)silicon 2,3-naphthalocyanine (isoBOSINC) is a representative of a group of naphthalocyanine derivatives with spectral and photophysical properties that make them attractive candidates for photodynamic therapy (PDT). Tissue distributions were studied in normal and in tumor-bearing rats as a function of time following intravenous injection of isoBOSINC as a suspension in 10% Tween 80 in saline. The dose studied was 0.25 mg/kg of body weight. The compound isoBOSINC was isolated from several tissues and organs, as well as tumors and peritumoral muscles and skin, and quantitated by a high-performance liquid chromatographic technique. The tumor model, an N-(4-[5-nitro-2-furyl]-2-thiazolyl)formamide (FANFT)-induced urothelial cell carcinoma, was transplanted into the hind legs of Fischer 344 rats. The dye was retained in tumors at higher concentrations than in all tissues and organs examined, except for spleen and liver. The highest concentration ratio of dye in tumor versus peritumoral muscle (24.5) occurred 9 h after injection. Serum clearance of isoBOSINC showed similar kinetic behavior for both groups of rats, with a t 1/2 of elimination of approximately 10 h. At 7 and 14 days postinjection, the levels of dye found in testes were generally higher than in most other tissues, except spleen and liver. Concentrations of isoBOSINC were either very low or not detectable in rat brain. Trace amounts of the dye were excreted in the urine, and by day 14 approximately 17% of the dose was accounted for in the feces. The significant levels of the drug in tumors, as well as the excellent ratios of tumor-to-muscle concentration observed, have promising implications for PDT of tumors.

Photodynamic therapy of B16 pigmented melanoma with liposome-delivered Si(IV)-naphthalocyanine.

The possibility of extending photodynamic therapy to the treatment of highly pigmented neoplastic lesions was tested by using Si(IV)-naphthalocyanine (SiNc) as a tumor-localizing agent. Si(IV)-naphthalocyanine displays intense absorbance at 776 nm (epsilon = 5 x 10(5) M-1 cm-1), where melanin absorption becomes weaker. As an experimental model we selected B16 pigmented melanoma subcutaneously transplanted to C57BL mice. Upon injection of 0.5 or 1 mg kg-1 of liposome-incorporated SiNc, maximal accumulation of the photosensitizer in the tumor was observed at 24 h with recoveries of 0.35 and 0.57 microgram g-1, respectively. However, the tumor targeting by SiNc shows essentially no selectivity, since the photosensitizer concentrations in the skin (peritumoral tissue) were very similar to those found in the tumor at all postinjection times examined by us. Irradiation of SiNc-loaded melanoma with 776 nm light from a diode laser at 24 h postinjection induces tumor necrosis and delay of tumor growth. The effect appears to be of purely photochemical nature at dose rates up to 260 mW cm-2; at higher dose rates, thermal effects are likely to become important.

Quenching of singlet molecular oxygen by phthalocyanines and naphthalocyanines.

Using the direct measurement of the photosensitized luminescence of singlet molecular oxygen (1O2) the rate constants (kq) have been determined for 1O2 quenching by the monomeric molecules of the following phthalocyanines and naphthalocyanines in chloroform: tetra-(4-tert-butyl) phthalocyanine (I); octa-(3,6-butoxy) phthalocyanine (II), tetra-(6-tert-butyl)-2,3 naphthalocyanine (III), aluminium tetra-(1-tert-phenyl)-2,3 naphthalocyanine (IV), tri-(n-hexyl-siloxy) derivatives of silicon- (V), tin- (VI), aluminium- (VII) and gallium- (VIII) 2,3 naphthalocyanine. The following kq values were obtained (kq x 10(-8) M-1 s-1): 2.9 (I), 59 (II), 100 (III), 20 (IV), 3.9 (V), 53 (VI), 33 (VII), 110 (VIII). As most of the quenchers have the low-lying triplet levels, a contribution of the quenching mechanism based on the energy transfer from 1O2 to these levels has been analysed. A formula is proposed describing the relation between kq values caused by this mechanism, and photophysical constants of the quencher triplet state. This formula was applied to phthalocyanines, naphthalocyanines, beta-carotene and bacterochlorophyll a. The data suggest that the energy transfer can fully explain the activity of V and strongly contributes into the activities of II, III and VI-VIII. A charge transfer interaction might be an additional mechanism involved in 1O2 quenching by compounds studied. As some phthalocyanines and naphthalocyanines are strong physical quenchers of singlet oxygen they can be used as efficient inhibitors for photodestructive processes in photochemical systems.

Protection by the fluoride ion against phthalocyanine-induced photodynamic killing of Chinese hamster cells.

When a dilute F- solution was added to a culture of Chinese hamster cells that had been preincubated with an aluminium phthalocyanine sensitizer derived from AlPcCl, the photosensitivity of the cells was markedly reduced compared to control cells not treated with F-. Under the same treatment conditions, the reduction in [3H]thymidine incorporation into cellular DNA caused by light and this sensitizer and the production of DNA-protein crosslinks caused by light and this sensitizer were also inhibited by F-. In contrast, the killing of Chinese hamster cells, the reduction of thymidine incorporation by the cells, and the production of DNA-protein crosslinks in the cells caused by the combination of light and either Photofrin II or the silicon phthalocyanine HOSiPcOSi(CH3)2(CH2)3-N(CH3)2 were not inhibited by F-. We conclude that the aluminium phthalocyanine sensitizer used is largely or completely AlPc(OH)(H2O), that it is converted to a fluoro complex by F-, and that this compound probably is a less efficient generator of photochemical damage at a critical cellular target(s) than is AlPc(OH)(H2O). The inhibition of thymidine incorporation and DNA-protein crosslink formation indicates that the effects of F- can be expressed at intracellular sites. It is further concluded that the silicon phthalocyanine sensitizer and Photofrin II do not interact significantly with F-.

Unusually high affinity of Zn(II)-tetradibenzobarrelenooctabutoxy-phthalocyanine for low-density lipoproteins in a tumor-bearing mouse.

An important factor in determining the efficacy of photosensitizing compounds in photodynamic therapy of tumors is the level to which tumors take up the photosensitizers after systemic injection. This parameter seems to be related to the transport modalities of the photosensitizer in the bloodstream. In this work the photosensitizer Zn(II)-tetradibenzobarrelenooctabutoxyphthalocyanine was shown to have an unprecedentedly high association with low-density lipoproteins (71% of the phthalocyanine in the plasma) when delivered in Cremophor micelles to tumor-bearing mice. This was accompanied by a particularly high tumor uptake at 24 h post-injection.

Inactivation of Trypanosoma cruzi trypomastigote forms in blood components by photodynamic treatment with phthalocyanines.

Three phthalocyanine dyes HOSiPcOSi(CH3)2(CH2)3N(CH3)2 (Pc 4), HOSiPcOSi(CH3)2(CH2)3N+(CH3)3I- (Pc 5) and aluminum tetrasulfophthalocyanine hydroxide (AlOHPcS4) were evaluated for their ability to inactivate the trypomastigote form of Trypanosoma cruzi in fresh frozen plasma (FFP) and red blood cell concentrates (RBCC). The compound Pc 4 was found to be highly effective in killing T. cruzi, Pc 5 less effective and AlOHPcS4 ineffective. With FFP as the medium, a complete loss of parasite infectivity in vitro (> or = 5 log10) was found to occur with 2 microM Pc 4 after irradiation with red light (> 600 nm) at a fluence of 7.5 J/cm2, while with RBCC as the medium, a complete loss was found to occur at a fluence of 15 J/cm2. Even without illumination, Pc 4 at 2 microM also killed about 3.7-4.1 log10 of T. cruzi in FFP during 30 min. Observed differences in T. cruzi killing by the various phthalocyanines may related to differences in binding; Pc 4 binds to the parasites about twice as much as Pc 5. Ultrastructural analysis of treated parasites suggests that mitochondria are a primary target of this photodynamic treatment. The data indicate that Pc 4 combined with exposure to red light could be used to eliminate bloodborne T. cruzi parasites from blood components intended for transfusion. The inactivation of T. cruzi by Pc 4 in the dark suggests a possible therapeutic application.