Tin etiopurpurin dichloride-sensitized lipid photooxidation of erythrocyte membranes

Sn(iv) Schiff base complexes: triplet photosensitizers for photoredox reactions

We present the synthesis and characterization of a series of four fluorescent Sn(iv) Schiff base complexes, which also possess long-lived triplet excited states.

Stability of Tin Etiopurpurin¶

Formulations of the tin etiopurpurin (SnET2) have been observed to undergo a spectral change on storage in dimethylformamide solution. This results in an alteration in the action spectrum, with enhanced photodynamic activity at lower wavelengths and decreased activity at 660 nm. On the basis of structural considerations, a reduced analog of SnET2 was prepared with an absorbance maximum at 640 nm. Formation of this product, termed SnET2H(2) relieves steric strain inherent in the parent molecule. Nuclear magnetic resonance, spectral and photodynamic data are consistent with the formation of SnET2H(2) during SnET2 storage. Slight modifications in the original synthesis are also reported, resulting in improved yields of intermediate products.

Purpurins and benzochlorins as sensitizers for photodynamic therapy

Purpurins and benzochlorins are hydrophobic second generation photosensitizers, which have sizable absorption in the 650-780 nm range and exhibit photodynamic activity against tumors after visible light treatment. This review summarizes the published data regarding these compounds: from the spectroscopic, photophysical and photochemical characteristics to the in vivo and in vitro photodynamic inactivation of tumors and normal tissue effects. Some mechanistic studies using both the Sn-etiopurpurin and/or the Cu-benzochlorin derivatives are also reviewed.

In situ comparison of 665 nm and 633 nm wavelength light penetration in the human prostate gland

The depth of treatment in photodynamic therapy (PDT) of tumors varies with the wavelength of light activating the photosensitizer. New generation photosensitizers that are excited at longer wavelengths have the potential for increasing treatment depths. Tin ethyl etiopurpurin (SnET2), a promising second-generation photosensitizer is maximally activated at 665 nm, which may be significantly more penetrating than 633 nm light currently used with porphyrins in PDT. The penetration of 665 nm and 633 nm wavelength red light in the prostate gland was compared in 11 patients undergoing prostatic biopsies for suspected prostatic cancer. Interstitial optical fibers determined the light attenuation within the prostate gland. Of the 11 patients, 7 had dual wavelength and 4 had single wavelength studies. The mean attenuation coefficients, mueff, for 665 nm and 633 nm wavelength light were 0.32 +/- 0.05 mm-1 and 0.39 +/- 0.05 mm-1, respectively, showing a statistically significant difference (P = 0.0003). This represented a 22% increase in the mean penetration depth and at 10 mm from the delivery fiber there was 1.8 times as much 665 nm light fluence than 633 nm. The mean mueff at 665 nm for benign and malignant prostate tissue were similar (P = 0.42), however, there was significant interpatient variation (mueff ranging from 0.24 to 0.42 mm-1) reflecting biological differences of therapeutic importance. The enhanced light fluence and penetration depth with 665 nm light should allow significantly larger volumes of prostatic tissue to be treated with SnET2-mediated PDT.

Antioxidant effect of inorganic ions on UVC and UVB induced lipid peroxidation

Phosphate buffer suspensions of unilamellar liposomes of phosphatidylcholine were irradiated with UVC (254 nm) and UVB (300 nm) light. The irradiation provoked lipid peroxidation and liposome lysis with release of entrapped glucose-6-phosphate. At the same intensity of absorbed light, the photochemical effect at 254 nm is higher than at 300 nm. The addition of copper(II) and manganese(II) reduced both the peroxidation and the lysis. The copper showed an inhibitory effect only on the process provoked by the 254 nm irradiation, whereas the manganese was efficient both at 254 and 300 nm. The results are interpreted with a mechanism of peroxidation and quenching, involving photoformation of peroxyl radicals that are scavenged by manganese(II) and copper(I), with consequent breaking of the radical chain and reduction of the peroxidation rate. The copper(I), which is the active species, can be formed only at 254 nm by electron capture. The experimental data fit the kinetic equations obtained by the proposed mechanism by means of computer software.

Iminium salt of copper benzochlorin (CDS1), a novel photosensitizer for photodynamic therapy: mechanism of cell killing

The mechanism of cell killing by CDS1, an iminium salt of octaethylbenzochlorin with copper in the aromatic ring, in combination with light from a noncoherent light source was investigated. Using a standard clonogenic assay and the AY-27 FANFT tumor line, photoactivation of CDS1 was shown to be cytotoxic. The photodynamic cell killing ability of CDS1 required the presence of molecular oxygen. The reactive species generated by light activation of CDS1 were effectively quenched by N,N'-diphenyl-p-phenylenediamine. Additionally, the photodynamic effect of CDS1 was not enhanced by deuterium oxide. To characterize the reactive oxygen species generated by the photoactivation of CDS1 the well-characterized erythrocyte ghost model was used. Superoxide dismutase and catalase were potent inhibitors of CDS1-induced lipid peroxidation of erythrocyte membranes. Sodium azide only partially inhibited lipid peroxidation. These findings differed from the known singlet oxygen generator, tin (II) etiopurpurin dichloride (SnET2). Sodium azide was a potent inhibitor of SnET2-induced lipid peroxidation, whereas superoxide dismutase and catalase were totally ineffective. Based on these results, we conclude that CDS1 requires the presence of molecular oxygen for cell killing to occur but appears to act primarily through a non-singlet oxygen mechanism.