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.

Quantification of the selective retention of palladium octabutoxynaphthalocyanine, a potential photothermal drug, in mouse tissues.

Palladium octabutoxynaphthalocyanine (PdNc(OBu)8) is a potential photothermal therapy (PTT) agent, absorbing strongly in the near-infrared region with no ability to induce photodynamic-type sensitisation (unlike many related napthalocyanines). We report here on the application of high pressure liquid chromatography (HPLC) with near-infrared absorption detection for the determination of the tissue accumulation and clearance of PdNc(OBu)8 in a tumour-bearing mouse model (Balb/c mice with EMT6 carcinoma tumour). Due to its insolubility in aqueous-based solvents, the drug was delivered intraperitoneally in a Cremophor-containing vehicle. Good selective accumulation of the drug into the tumour versus muscle or skin is observed, with the best combination of selectivity and tumour concentration occurring at 24-72 h after drug administration. Clearance times are quite long. Comparison with other similar drugs as reported in the literature indicates that the Cremophor-containing vehicle is likely in large part responsible for the observed pharmacokinetic behaviour. This drug shows potential for PTT and will be investigated further for therapy in this animal model.

Phthalocyanine 4 (Pc 4) photodynamic therapy of human OVCAR-3 tumor xenografts.

Photodynamic therapy (PDT) is a cancer treatment modality utilizing a photosensitizer, light and oxygen. Photodynamic therapy with Photofrin has been approved by the U.S. Food and Drug Administration for treatment of advanced esophageal and early lung cancer. Because of certain drawbacks associated with the use of Photofrin, there is a need to identify new photosensitizers for human use. The photosensitizer Pc 4 (HOSiPc-OSi[CH3]2[CH2]3N[CH3]2) has yielded promising PDT effects in many in vitro and in vivo systems. The aim of this study was to assess the usefulness of Pc 4 as a PDT photosensitizer for a human tumor grown as a xenograft in athymic nude mice. The ovarian epithelial carcinoma (OVCAR-3) was heterotransplanted subcutaneously in athymic nude mice. Sixty mice bearing OVCAR-3 tumors (approximately 80-130 mm3) were divided into six groups of 10 animals each, three for controls and three for treatment. The Pc 4 was given by tail vein injection, and 48 h later a 1 cm area encompassing the tumor was irradiated with light from a diode laser coupled to a fiberoptic terminating in a microlens (lambda = 672 nm, 150 J/cm2, 150 mW/cm2). Tumors of control animals receiving no treatment, light alone or Pc 4 alone continued to grow. Of animals receiving 0.4 mg/kg Pc 4 and light, one (10%) had a complete response and was cured (no regrowth up to 90 days post-PDT), while all others (90%) had a partial response and were delayed in regrowth. Of animals receiving 0.6 mg/kg Pc 4 and light, eight (80%) had a complete response, and two of these were cured. Of animals receiving 1.0 mg/kg Pc 4 and light, six (60%) had a complete response, and two of these were cured. In additional experiments, tumors from animals treated with Pc 4 (1 mg/kg) and light were removed 15, 30, 60 and 180 min post-PDT, and from these tumors DNA and protein were extracted. Agarose gel electrophoresis revealed the presence of apoptotic DNA fragmentation as early as 15 min post-PDT. Western blotting showed the cleavage of the 116 kDa native poly(ADP-ribose) polymerase (PARP) into fragments of approximately 90 kDa, another indication of apoptosis, and the presence of p21/WAF1/CIP1 (p21) in all PDT-treated tumors. These changes did not occur in control tumors. Pc 4 appears to be an effective photosensitizer for PDT of human tumors grown as xenografts in nude mice. Early apoptosis, as revealed by PARP cleavage, DNA fragmentation and p21 overexpression, may be responsible for the excellent Pc 4-PDT response. Clinical trials of Pc 4-PDT are warranted.

Photothermal sensitization of amelanotic melanoma cells by Ni(II)-octabutoxy-naphthalocyanine.

Incubation of B78H1 amelanotic melanoma cells with a potential photothermal sensitizer, namely, liposome-incorporated Ni(II)-octabutoxy-naphthalocyanine (NiNc), induces an appreciable cellular accumulation of the naphthalocyanine, which is dependent on both the NiNc concentration and the incubation time. No detectable decrease in cell survival occurs upon red-light irradiation (corresponding to the longest-wavelength absorption bands of NiNc) in a continuous-wave (c.w.) regime of the naphthalocyanine-loaded cells. On the other hand, 850 nm irradiation with a Q-switched Ti:sapphire laser operating in a pulsed mode (30 ns pulses, 10 Hz, 200 mJ/pulse) induces an efficient cell death. Thus, ca. 98% decrease in cell survival is obtained upon 5 min irradiation of cells that have been incubated for 48 h with 5.1 microM NiNc. The efficiency of the photoprocess is strongly influenced by the NiNc cell incubation time prior to irradiation. Photothermal sensitization with NiNc appears to open new perspectives for therapeutic applications, as suggested by preliminary in vivo studies with C57/BL6 mice bearing a subcutaneously implanted amelanotic melanoma.

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).

Photoinactivation of amelanotic and melanotic melanoma cells sensitized by axially substituted Si-naphthalocyanines.

The photosensitizing activity of the new far-red absorbing naphthalocyanine SiNc [OSi (n-C10H21)3] [OSi(CH3)2(CH2)3N(CH3)2], (DAP-SiNc), and of its analogue SiNc [OSi(i-C4H9)2(n-C18H37)]2, (IsoBO-SiNc), was studied with two cell variants of B16 melanoma, the amelanotic clone B78H1 and the highly pigmented B16F1 cells. Upon excitation with a 776 nm diode laser, DAP-SiNc appeared to be a markedly more efficient photosensitizer than isoBO-SiNc. The higher photoefficiency of DAP-SiNc was likely to reflect its accumulation in significantly larger amounts by both cell types, as well as a much smaller tendency to undergo aggregation when bound to the cells. In any case, melanotic cells were less sensitive to the photoinactivating action of DAP-SiNc: the protective action of melanin was a consequence of an optical filtering of the 776 nm light and an appreciable shortening of the DAP-SiNc triplet lifetime (40 microseconds for the amelanotic vs. 17 microseconds for the melanotic cells). Functional and morphological studies on irradiated cells showed that cell death due to DAP-SiNc photosensitization was mainly correlated with the modification of targets located in the lysosomes and the cytoplasmic membrane.

A comparative analysis of silicon phthalocyanine photosensitizers for in vivo photodynamic therapy of RIF-1 tumors in C3H mice.

Photofrin photodynamic therapy (PDT) has recently received FDA approval for the palliative treatment of totally and partially obstructing esophageal malignancies. However, there is a need for new PDT photosensitizers because Photofrin has a number of undesirable features. The purpose of this study was to evaluate the efficacy of four amine-bearing silicon phthalocyanines--Pc4, Pc10, Pc12 and Pc18--as potential PDT photosensitizers. Equimolar concentrations of these Pc were found to be highly effective at causing the regression of RIF-1 tumors transplanted to C3H/HeN mice. The amount of Pc4 necessary to cause an equivalent amount of tumor regression in this model system was substantially less than the amount of Photofrin. The cutaneous phototoxicity of the silicon Pc photosensitizer was assessed by the utilization of the murine ear-swelling model. When C3H mice were exposed to 167 J/cm2 of polychromatic visible light from a UVB-filtered solar simulator, which emitted UV radiation and visible light above 320 nm, the Pc produced little, if any, cutaneous photosensitivity. These results indicate that Pc4, Pc10, Pc12 and Pc18 are at least as effective as Photofrin in PDT protocols, while at the same time addressing many of the drawbacks of Photofrin.

Pharmacokinetic and phototherapeutic properties of axially substituted Si(IV)-tetradibenzobarreleno-octabutoxyphthalocyanines.

Three Si(IV)-tetradibenzobarreleno-octabutoxyphthalocyanines (TDiBOPcs) bearing different axial ligands on the metal ion were studied for their tumour-localizing and-photosensitizing properties after i.v. injection via a Cremophor emulsion (0.35 mumol kg-1 b.w.) to Balb/c mice bearing an intramuscularly implanted MS-2 fibrosarcoma. In all cases, the maximum tumour accumulation of the photosensitizer (0.8-1.9 nmol g-1 of tissue) was found at 24 h after injection. The efficiency and selectivity of tumour targeting appeared to be dependent on the nature of the axial ligands; optimal values of these parameters were obtained in the case of the bis(trihexyl-siloxy)-substituted Si(IV)-TDiBOPc, which gave a 7-9 tumour/muscle ratio of phthalocyanine concentration at 24-48 h after injection. The extent of tumour response to PDT treatment was correlated with the concentration of the photosensitizer in the tumour tissue: upon 740 nm irradiation (180 mW cm-2, 200 J cm-2) at 48 h after injection of 0.35 mumol kg-1 of Si(IV)-TDiBOPc-C6H13, the tumour growth exhibited a delay of about 7 days.

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.

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.

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.

High-performance liquid chromatographic determination of the silicon phthalocyanine Pc 4 in human blood.

A sensitive and reproducible method has been developed for the measurement of the silicon phthalocyanine Pc 4 in red blood cell concentrates (RBCC). The procedure involves extraction of the RBCC with acetonitrile, purification of the extracts with reversed-phase Sep-Pak C18 cartridges and determination of Pc 4 in the extracts by high-performance liquid chromatography (HPLC) using a reversed-phase C18 column. The detection limit with 1-ml RBCC samples is 2 ng. This method is applicable to monitoring Pc 4 during its use as a photosensitizer for the inactivation of viruses in RBCC prior to transfusion. It has the potential to be adapted for measuring Pc 4 in tissues during its use in photodynamic therapy of cancer.

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 axial ligation and delivery system on the tumour-localising and -photosensitising properties of Ge(IV)-octabutoxy-phthalocyanines.

Four Ge(IV)-octabutoxy-phthalocyanines (GePcs) bearing two alkyl-type axial ligands were assayed for their pharmacokinetic properties and phototherapeutic efficiency in Balb/c mice bearing an intramuscularly transplanted MS-2 fibrosarcoma. The GePcs were i.v. injected at a dose of 0.35 mumol kg-1 body weight after incorporation into either Cremophor emulsions or small unilamellar liposomes of dipalmitoyl-phosphatidylcholine (DPPC). Both the nature of the delivery system and the chemical structure of the phthalocyanine were found to affect the behaviour of the GePcs in vivo. Thus, Cremophor-administered GePcs invariably yielded a more prolonged serum retention and a larger association with low-density lipoproteins (LDLs) as compared with the corresponding liposome-delivered phthalocyanines. This led to a greater efficiency and selectivity of tumour targeting. These effects were more pronounced for those GePcs having relatively long alkyl chains (hexyl to decyl) in the axial ligands. Maximal tumour accumulation (0.67 nmol per g of tissue) was found for Ge-Pc(hexyl)2 at 24 h after injection. Consistently, the Ge-Pc(hexyl)2, administered via Cremophor, showed the highest phototherapeutic activity towards MS-2 fibrosarcoma.

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.

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.

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.

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 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.

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.