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The oxidation of tryptophan photosensitized by PtCl6(2-) has been investigated in aqueous solutions at different pH using nanosecond laser flash photolysis. Cationic and neutral radicals of tryptophan were detected at pH 2.8 and 8.5, respectively. The generation of the radical was attributed to oxidation by Cl2- that was formed from the homolytic bond cleavage in the excited state of PtCl6(2-). The bimolecular rate constant derived from the kinetics analysis, 2.8 +/- 0.2 x 10(9) M-1 s-1, is in good agreement with the value obtained in earlier pulse radiolysis studies. Both the cationic and neutral radicals decayed by second-order kinetics, consistent with the dimerization process.

Cu(II)-hematoporphyrin (CuHp) was efficiently accumulated by B78H1 amelanotic melanoma cells upon incubation with porphyrin concentrations up to 52 microM. When the cells incubated for 18 h with 13 microM CuHp were irradiated with 532 nm light from a Q-switched Nd: YAG laser operated in a pulsed mode (10 ns pulses, 10 Hz) a significant decrease in cell survival was observed. The cell photoinactivation was not the consequence of a photodynamic process, as CuHp gave no detectable triplet signal upon laser flash photolysis excitation and no decrease in cell survival was observed upon continuous wave irradiation. Thus, it is likely that CuHp sensitization takes place by photothermal pathways. The efficiency of the photoprocess was modulated by different parameters; thus, while varying the amount of added CuHp in the 3.25-26 microM range had little effect, pulse energies larger than 50 mJ and irradiation times of at least 120 s were necessary to induce a cell inactivation of about 50%. The porphyrin-cell incubation time prior to irradiation had a major influence on cell survival, suggesting that the nature of the CuHp microenvironment can control the efficiency of photothermal sensitization.

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).

Four silicon phthalocyanine photosensitizers have been prepared and studied in an effort to learn more about the structural features that a silicon phthalocyanine must have in order to be a good photodynamic therapy (PDT) photosensitizer. The compounds that have been studied are the known phthalocyanines HOSiPcOSi(CH3)2-(CH2)3N(CH3)2, Pc 4; and SiPc[OSi(CH3)2(CH2)3N(CH3)2]2, Pc 12; and the new photosensitizers HOSiPcOSi(CH3)2- (CH2)3N(CH2CH3)(CH2)2N(CH3)2, Pc 10; and SiPc[OSi (CH3)2(CH2)3N(CH2CH3)(CH2)2N(CH3)2]2, Pc 18. The triplet lifetimes of the four photosensitizers, their singlet oxygen quantum yields, their ability to photoenhance the generation of lipid peroxidation products in human erythrocyte ghosts, their ability to partition into V79 cells and their ability to photokill V79 and L5178Y-R cells have been determined. It is concluded that the presence of a small axial ligand (e.g. an OH ligand) is not necessary for efficient photosensitization, the presence of two aminosiloxy ligands generally provides at least as good photosensitization as one such ligand, and the presence of an elongated diaminosiloxy axial ligand rather than a short aminosiloxy ligand is less desirable. Further, it is concluded that the presence of structural features leading to improvement in the association between the photosensitizers and important cellular targets are more useful than those leading to improvements in their already acceptable photophysical and photochemical properties.

Tris (2,2'-bipyridyl)ruthenium(II)chloride hexahydrate (Ru[bpy]3(2+)) free in solution and adsorbed onto antimony-doped SnO2 colloidal particles was used as a photosensitizer for a comparison of the O2(1 delta g) and electron-transfer-mediated photooxidation of tryptophan (TRP), respectively. Quenching of excited Ru(bpy)3(2+) by O2(3 sigma g-) in an aerated aqueous solution leads only to the formation of O2(1 delta g) (phi delta = 0.18) and this compound was used as a type II photosensitizer. Excitation of Ru(bpy)3(2+) adsorbed onto Sb/SnO2 results in a fast injection of an electron into the conduction band of the semiconductor and accordingly to the formation of Ru(bpy)3(2+) and was used for the sensitization of the electron-transfer-mediated photooxidation. The Ru(bpy)3(3+) is reduced by TRP with a bimolecular rate constant kQ = 5.9 x 10(8) M-1 s-1, while O2(1 delta g) is quenched by TRP with kt = 7.1 x 10(7) M-1 s-1 (chemical + physical quenching). Relative rate constants for the photooxidation of TRP (kc) via both pathways were determined using fluorescence emission spectroscopy. With Np, the rate of photons absorbed, being constant for both pathways we obtained kc = (372/Np) M-1 s-1 for the O2(1 delta g) pathway and kc > or = (25,013/Np) M-1 s-1 for the electron-transfer pathway, respectively. Thus the photooxidation of Trp is more than two orders of magnitude more efficient when it is initiated by electron transfer than when initiated by O2(1 delta g).

The synthesis, preliminary in vivo biological activity, singlet oxygen and fluorescence yields of a series of alkyl ether derivatives of chlorophyll-alpha analogs are described. For short-chain carbon ethers (1-7 carbon units), it was observed that the biological activity increased by increasing the length of the carbon chain, being maximum in compounds with n-hexyl and n-heptyl chains. Related sensitizers prepared by reacting 2-(1-bromoethyl)-2-devinylpyropheophorbide-alpha with (sec)alcohols were found to be less effective. Under similar treatment conditions, photosensitizers containing cis- and trans- 3-hexenyl side chains were ineffective. Thus, both stereochemical and steric factors caused differences in sensitizing activity. In general, pyropheophorbide-alpha analogs were found to be more active than related chlorin e6 derivatives, in which the isocyclic ring (ring "E") was cleaved. Related photosensitizers in the 9-deoxy- series were found to be as effective as the corresponding pyropheophorbide-alpha analogs. The photosensitizers prepared from pyropheophorbide-alpha methyl ester and chlorin e6 trimethyl ester have long wavelength absorption at 660 nm (epsilon 45 000 to 50 000). Reduction of the carbonyl group in the pyropheophorbide-alpha to methylene (ring E) resulted in a blue shift to 648 nm (epsilon 38 000).

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.

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.

The current trend in methodology for determining IR and near-IR absorption spectra is to employ interferometer-based instruments to replace the monochromator-based devices used heretofore. As a dispersion element, the interferometer offers major improvements in spectral resolution (Connes advantage), light throughput (Jacquinot advantage) and data acquisition through multiplexing (Felgett advantage). We have compared signal-to-noise (S/N) ratios of grating-based and interferometer-based instruments for making spectral determinations of near-IR luminescence. Our results show that under identical excitation and detector conditions the interferometer instrument easily outperforms the grating, giving a 10-fold improvement in S/N at high signal amplitude (A488nm = 0.97) and a 20-fold improvement when the signal amplitude is low (A488nm = 0.06). Although some spectral resolution is sacrificed when scan times on the Fourier transform (FT)IR are significantly shortened, the S/N ratio was found only to decrease by a factor of 2 for a 10-fold decrease in scan time. This adds to the advantages of the FTIR technique because the S/N will thus improve for the same total acquisition time.

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.

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.

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.

The 5 microM hematoporphyrin-sensitized photooxidation of 1,3-diphenylisobenzofuran (DPBF) was studied in homogeneous ethanolic solutions and in aqueous dispersions of unilamellar liposomes of dipalmitoylphosphatidylcholine; both the porphyrin and DPBF are embedded in the phospholipid bilayer. The rate and quantum yield of DPBF photooxidation were found to increase upon increasing the substrate concentration and were higher in the liposome system, while they were unaffected by the fluidity of the phospholipid bilayer. Time-resolved spectroscopic measurements showed that the photooxidation of DPBF in ethanol solution proceeds by a type II O2(1 delta g)-involving mechanism. In the liposomal vesicles the high local concentration of hematoporphyrin (Hp) and DPBF in the phospholipid bilayer (ca 2000-fold higher than the stoichiometric concentration) enhances the probability of energy transfer from triplet Hp to DPBF with generation of triplet DPBF; hence O2 (1 delta g) formation can be promoted by both triplet Hp and triplet DPBF. A minor fraction of triplet DPBF quenchings appears to generate radical species which propagate DPBF damage by chain reaction.

Several types of glass and plastic materials were shown to exhibit intense photoluminescence when irradiated with UV. Water or phosphate buffered saline (PBS) contained within vessels of the respective materials when irradiated, also demonstrated relatively long-lived luminescence. A significant percentage (30%) of cultured mammalian cells were killed when exposed to UV-irradiated glass beads. The nature of the luminescence of water or PBS, or whether this or the photoluminescence of glass is directly responsible for cell toxicity, is unknown. However, we call attention to this phenomenon as a potential complicating factor in photobiological studies.