Photosensitized Protein-Damaging Activity, Cytotoxicity, and Antitumor Effects of P(V)porphyrins Using Long-Wavelength Visible Light through Electron Transfer

Photodynamic therapy (PDT) is a less-invasive treatment for cancer through the administration of less-toxic porphyrins and visible-light irradiation. Photosensitized damage of biomacromolecules through singlet oxygen (¹O₂) generation induces cancer cell death. However, a large quantity of porphyrin photosensitizer is required, and the treatment effect is restricted under a hypoxic cellular condition. Here we report the phototoxic activity of P­(V)­porphyrins: dichloroP­(V)­tetrakis­(4-methoxyphenyl)­porphyrin (CLP­(V)­TMPP), dimethoxyP­(V)­tetrakis­(4-methoxyphenyl)­porphyrin (MEP­(V)­TMPP), and diethyleneglycoxyP­(V)­tetrakis­(4-methoxyphenyl)­porphyrin (EGP­(V)­TMPP). These P­(V)­porphyrins damaged the tryptophan residue of human serum albumin (HSA) under the irradiation of long-wavelength visible light (>630 nm). This protein photodamage was barely inhibited by sodium azide, a quencher of ¹O₂. Fluorescence lifetimes of P­(V)­porphyrins with or without HSA and their redox potentials supported the electron-transfer-mediated oxidation of protein. The photocytotoxicity of these P­(V)­porphyrins to HeLa cells was also demonstrated. CLP­(V)­TMPP did not exhibit photocytotoxicity to HaCaT, a cultured human skin cell, and MEP­(V)­TMPP and EGP­(V)­TMPP did; however, cellular DNA damage was barely observed. In addition, a significant PDT effect of these P­(V) porphyrins on a mouse tumor model comparable with the traditional photosensitizer was also demonstrated. These findings suggest the cancer selectivity of these P­(V)­porphyrins and lower carcinogenic risk to normal cells. Electron-transfer-mediated oxidation of biomacromolecules by P­(V)­porphyrins using long-wavelength visible light should be advantageous for PDT of hypoxic tumor

Synthesis, Photophysical Properties, and Biological Evaluation of <i>trans</i>-Bisthioglycosylated Tetrakis(fluorophenyl)chlorin for Photodynamic Therapy

<i>trans</i>-Bisthioglycosylated tetrakis­(fluoro­phenyl)­chlorin (<b>7</b>) was designed as a powerful photodynamic therapy (PDT) photosensitizer based on the findings of our systematic studies. We show here that the <i>trans</i>-bisthioglycosylated structure of <b>7</b> enhanced its uptake by HeLa cells and that the chlorin ring of <b>7</b> increased the efficiency of reactive oxygen species generation under the standard condition of our photocytotoxicity test. The versatility of <b>7</b> in PDT treatment was established using weakly metastatic B16F1 melanoma cells, metastatic 4T1 breast cancer cells, the RGK-1 gastric carcinoma mucosal cell line, and three human glioblastoma cell lines (U87, U251, and T98G). The pharmacokinetics of <b>7</b> in mice bearing 4T1 breast cancer cells showed a high tumor-to-skin concentration ratio (approximately 60) at 24 h after intraperitoneal injection. The PDT efficacy of <b>7</b> in vivo was approximately 250-times higher than that of mono-l-aspartyl chlorin e6 (<b>9</b>) in mice bearing 4T1 breast cancer cells

Sugar and Heavy Atom Effects of Glycoconjugated Chlorin Palladium Complex on Photocytotoxicity

Palladium­(II) complexes of glycoconjugated porphyrin and pyrrolidine-fused chlorin were prepared to examine sugar and heavy atom effects on <i>in vitro</i> photocytotoxicity. Cellular uptake into HeLa cells was enhanced by introducing sugar units regardless of other features, such as the central ion (free base or palladium­(II) ion) and the ring structure (porphyrin or chlorin). The palladium­(II) complex of glycoconjugated pyrrolidine-fused chlorin (PdPC<b>2</b>) exerted an excellent degree of photocytotoxicity not only on HeLa cells, but also on metastatic B16-BL6 cells, weakly metastatic B16F1 cells, and metastatic 4T1 cells. However, free-base glycoconjugated pyrrolidine-fused chlorin (PC<b>2</b>) also exerted similar or much higher photocytotoxicity rather than PdPC<b>2</b>. Therefore, the palladium­(II) ion did not improve the <i>in vitro</i> photocytotoxicity of PC<b>2</b>. The enhanced singlet oxygen generation of palladium­(II) complexes (i.e., the heavy atom effect) was confirmed at least in O₂-saturated D₂O. In addition, the formation of hydrogen peroxide and hydroxyl radical were also detected in O₂-saturated phosphate buffered saline. However, the reactive oxygen species (ROS) generation efficiency, which is the product of the (relative) quantum yield of each ROS and the light absorbing ability, did not fit the trends of photocytotoxicity seen for the photosensitizers. In our glycoconjugated photosensitizers tested, the best indicator of the photocytotoxicity was found to be the light absorbing ability (namely, the oscillator strength in the wavelength region applied in the photocytotoxicity test). These results indicated that photochemical characteristics of glycoconjugated photosensitizers were notably susceptible to the microenvironment. The biological characteristics, such as the sugar effect, were a much more reliable approach to improving the photocytotoxicity of photosensitizers