Maria Valles, Roberta Biolo, Raymond Bonnett, Magdalena Canete, Antonia Gomez, Giulio Jori, Angeles Juarranz, Kimberly McManus, Kawulia Okolo, M. Soncin, Angeles Villanueva
A family of benzoporphyrins formed by differently substituted metallo tetrabenzoporphyrins and one opp-dibenzoporphyrin has been prepared. The former benzoporphyrins, and meso- tetra(m-hydroxy-phenyl)chlorin (m-THPC) to act as reference, have been encapsulated into liposomes and subjected to preliminary in vitro and in vivo assays to test their efficacy as photosensitizers in the photodynamic therapy of cancer. The results of the photocytotoxicity test shows that, with the exception of the nickel complexes 5, and 7/8, the other porphyrins are photobiologically active, the Mg-tetrabenzoporphyrin 1 and the opp-dibenzoporphyrin 10 being the most active. The dark toxicity of the photoactive porphyrins is in the range described for many photosensitizers, including HPD. The in vivo assays show no toxicity in the liver for any of the compounds tested, and also that 2 is the most promising photosensitizer among them, because of an efficient localization in an experimental mouse tumor.
The liposomal zinc(II) phthalocyanine (Zn-Pc) formulation CGP55847 was administered intravenously (0.5 mg Zn-Pc/kg) to C57/BL6 mice bearing subcutaneously implanted B16 melanomas or to Swiss mice bearing intramuscularly implanted Ehrlich carcinomas. Tumors were removed 3 or 24 h after dosing, and the Zn-Pc content and intratumoral distribution determined by extraction and quantitative fluorescence microscopy. Localization of the photosensitizer within the tumor mass occurred more rapidly in the highly vascularized Ehrlich carcinoma compared to the less highly vascularized B16 melanoma. Zn-Pc was evident in and around blood vessels 3 but not 24 h after dosing. More Zn-Pc was found in necrotic areas compared to viable tumor tissue; little or no Zn-Pc was detected in the muscle tissue invaded by the Ehrlich carcinoma. At the cellular level, Zn-Pc was associated with membranes and the cytosol but not the nucleus.
The mechanisms of photosensitized tumor destruction during photodynamic therapy (PDT) appear to be a complex interplay of processes involving several tissular components, such as malignant cells, microvasculature, specific blood constituents and non-vascular stroma. While vascular aberrations are of major importance when PDT is performed with Photofrin II, which is the photosensitizer most frequently used in clinical PDT, the initial pattern of tumor damage can be substantially modified by factors that alter the distribution of the photosensitizer in the neoplastic tissue. Such factors include the chemical structure of the photosensitizer, its physico-chemical properties (especially, the degree of hydrophobicity), the modality of its transport in the bloodstream, and the use of delivery systems.
A phthalocyanine derivative with two cholesterol moieties as axial ligands to the central Ge(IV) ion efficiently photosensitizes the oxidative modification of L-tryptophan. Administration of liposome-bound GePc to Balb/c mice bearing a MS-2 fibrosarcoma yields a quantitative release of the dye to serum lipoproteins, followed by a selective accumulation in the tumor as well as a low content in the skin. At 24 h after injection of 0.76 mg/kg GePc, the tumor was irradiated with 600 - 700 nm light; tumor necrosis appeared in all treated mice as a consequence of extensive damage of cellular and stromal elements.
An octakis-decyl-substituted Zn(II)-phthalocyanine (ZnODPc) was prepared by chemical synthesis and was shown to possess favorable photophysical properties to act as a photodynamic agent. Intravenous injection of ZnODPc incorporated into Cremophor emulsions (1.2 or 2.4 mg/kg) to Balb/c mice bearing a MS-2 fibrosarcoma resulted in an efficient and selective accumulation of the phthalocyanine in the tumor. Illumination of the ZnODPc-loaded neoplastic lesion at 24 h after injection caused tumor regression as a result of both intracellular and intravascular damage.
Progress in the use of miniature optoelectronic systems based on Coherent-Light-Emitting- Diodes (CLEDs) and CLED-pumped solid-state lasers (Microlasers) is reported for: (1) retina photocoagulation with 800 nm diode lasers and 532 nm Nd:YAB Microlasers; (2) endoscopic photocoagulation of gastrointestinal tumors with an 800 nm high power multi-CLED system; (3) 800 nm diode laser-assisted microvascular anastomosis; (4) photodynamic therapy of tumors with 780 nm CLED and 660 nm LED.
During a 3 year period, 20 patients with morphologically proven squamous cell carcinoma of the trachea or bronchi have been treated by photoradiation therapy (PRT). A Bulgarian gold vapor laser and hematoporphyrin of `Jacopo Monico,' Italy were used. The photosensitizer was applied intravenously 24 - 48 h prior to PDT. The median realized energy dose was 410 J/cm2 for each patient with a middle power of 180 mW. In 5 of all the cases we performed two sessions. The obtained therapeutic results are as follows: CR -- one case (5%), SR -- 10 cases (50%), NR -- 3 cases (15%). The median survival of the patients with advanced cancer was 13.3 months. At the end of 1990 three patients were alive. Our experience shows that PRT is a promising palliative method in cases of advanced carcinoma for the recanalization of airways.
Zn(II)-phthalocyanine (ZnPc) is a tetraazaisoindole pigment which can be prepared by chemical synthesis with a high degree of purity, and it efficiently absorbs 680 nm of light. These properties, associated with its ability to generate activated oxygen species (e.g., singlet oxygen) upon photoexcitation, make ZnPc a potential phototherapeutic agent. Actually, upon delivery of ZnPc to tumor-bearing animals after incorporation into liposomal vesicles, the dye was uptaken and retained by the tumor tissue in significant amounts and with a good degree of selectivity. Irradiation of the ZnPc-loaded tumor area with ca. 680 nm of light caused tumor necrosis to an extent which was related to the dye concentration in the tumor.
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