Mei-Rong Ke

Preparation and in Vitro Photodynamic Activities of Folate-Conjugated Distyryl Boron Dipyrromethene Based Photosensitizers

Two folate-conjugated diiododistyryl boron dipyrromethenes have been prepared and characterized with various spectroscopic methods. These conjugates exhibit higher photocytotoxicity toward the KB human nasopharyngeal carcinoma cells, which have high expression of folate receptors when compared with the MCF-7 human breast adenocarcinoma cells, which have low expression of folate receptors. The difference in photocytotoxicity for these two cell lines is particularly large for the conjugate with a shorter oligoethylene glycol linker (compound 11a) as a result of its higher cellular uptake and slightly lower aggregation tendency. Its IC50 value toward KB cells (0.06 μM) is 43-fold lower than that for MCF-7 cells, while the difference is only 6-fold for the analogue with a longer linker (compound 11b). The length of the spacer also affects their subcellular localization. While compound 11a shows high affinity toward the endoplasmic reticulum of KB cells, conjugate 11b is mainly localized in the lysosomes.

A Phthalocyanine–Peptide Conjugate with High In Vitro Photodynamic Activity and Enhanced In Vivo Tumor‐Retention Property

A novel zinc(II) phthalocyanine conjugated with a short peptide with a nuclear localization sequence, Gly-Gly-Pro-Lys-Lys-Lys-Arg-Lys-Val, was synthesized by click chemistry and a standard Fmoc solid-phase peptide synthesis protocol. The conjugate was purified by HPLC and characterized with UV/Vis and high-resolution mass spectroscopic methods. Both this compound and its non-peptide-conjugated analogue are essentially non-aggregated in N,N-dimethylformamide and can generate singlet oxygen effectively with quantum yields (Φ(Δ)) of 0.84 and 0.81, respectively, relative to unsubstituted zinc(II) phthalocyanine (Φ(Δ) =0.56). Conjugation of the peptide sequence, however, can enhance the cellular uptake, efficiency in generating intracellular reactive oxygen species, and photocytotoxicity of the phthalocyanine-based photosensitizer against HT29 human colorectal carcinoma cells. The IC(50) value of the conjugate is as low as 0.21 μM. In addition, the conjugate shows an enhanced tumor-retention property in tumor-bearing nude mice. After 72 h post-injection, the dye concentration in the tumor was significantly higher than that in other organs. The results suggest that this phthalocyanine-peptide conjugate is a highly promising photosensitizer for photodynamic therapy.

Photodynamic inactivation of bacteria and viruses using two monosubstituted zinc(II) phthalocyanines

A zinc(II) phthalocyanine substituted with a triamino moiety and its tri-N-methylated analogue have been prepared and characterized with various spectroscopic methods. Both compounds remain non-aggregated in N,N-dimethylformamide and in water containing 0.05% Cremophor EL (v/v), and can generate singlet oxygen effectively. The photodynamic activities of these compounds have been examined against a range of bacterial strains, including the Gram-positive methicillin-sensitive Staphylococcus aureus ATCC 25923 and methicillin-resistant Staphylococcus aureus ATCC BAA-43, and the Gram-negative Escherichia coli ATCC 35218 and Pseudomonas aeruginosa ATCC 27853. Both photosensitizers are highly cytotoxic, particularly for the two Gram-positive strains, for which as low as 5 nM of dye is required to induce a 4-log reduction of their viability. The tri-N-methylated derivative has also been shown to be able to effectively inhibit the growth of a series of clinical strains of Staphylococcus aureus and Escherichia coli, and biofilms of methicillin-resistant Staphylococcus aureus ATCC 67928 and ATCC 68507, and Staphylococcus epidermidis ATCC 35984. In addition, the photodynamic inactivation of a range of viruses using these two compounds has also been investigated. Both compounds are highly photocytotoxic against the enveloped viruses influenza A virus (H1N1) and herpes simplex virus type 1 (HSV1), but exhibit no significant cytotoxicity toward the non-enveloped viruses adenovirus type 3 (Ad3) and coxsackievirus (Cox B1).

A pH-Responsive Layered Double Hydroxide (LDH)–Phthalocyanine Nanohybrid for Efficient Photodynamic Therapy

A pH-responsive nanohybrid (LDH-ZnPcPS4 ), in which a highly hydrophilic zinc(II) phthalocyanine tetra-α-substituted with 4-sulfonatophenoxy groups (ZnPcPS4 ) is incorporated with a cationic layered double hydroxide (LDH) based on electrostatic interaction, has been specially designed and prepared through a facile co-precipitation approach. ZnPcPS4 is an excellent singlet-oxygen generator with strong absorption at the near-infrared region (692 nm) in cellular culture media, whereas the photoactivities of ZnPcPS4 were remarkably inhibited after incorporation with the LDH. The nanohybrid is essentially stable in aqueous media at pH 7.4; nevertheless, in slightly acidic media of pH 6.5 or 5.0, ZnPcPS4 can be efficiently released from the LDH matrix, thus leading to restoration of the photoactivities. The nanohybrid shows a high photocytotoxicity against HepG2 cells as a result of much more efficient cellular uptake and preferential accumulation in lysosomes, whereby the acidic environment leads to the release of ZnPcPS4 . The IC50 value of LDH-ZnPcPS4 is as low as 0.053 μM, which is 24-fold lower than that of ZnPcPS4 . This work provides a facile approach for the fabrication of photosensitizers with high photocytotoxicity, potential tumor selectivity, and rapid clearance character.

A Tumor-pH-Responsive Supramolecular Photosensitizer for Activatable Photodynamic Therapy with Minimal In Vivo Skin Phototoxicity

A major challenge in photodynamic therapy (PDT) is the development of new tumor-targeting photosensitizers. The tumor-specific activation is considered to be an effective strategy for designing these photosensitizers. Herein, we describe a novel tumor-pH-responsive supramolecular photosensitizer, LDH-ZnPcS8, which is not photoactive under neutral conditions but is precisely and efficiently activated in a slightly acidic environment (pH 6.5). LDH-ZnPcS8 is prepared by using a simple coprecipitation method based on the electrostatic interaction between negatively charged octasulfonate-modified zinc(II) phthalocyanine (ZnPcS8) and cationic hydroxide layers of layered double hydroxide (LDH). The in vitro photodynamic activities of LDH-ZnPcS8 in cancer cells are dramatically enhanced relative to those of ZnPcS8 alone. The results of in vivo fluorescence imaging demonstrate that the nanohybrid is activated in tumor tissues, where it displays an excellent PDT effect resulting in 95.3% tumor growth inhibition. Furthermore, the minimal skin phototoxicity of LDH-ZnPcS8 highlights its high potential as a novel photosensitizer for activatable PDT.

Highly positive-charged zinc(II) phthalocyanine as non-aggregated and efficient antifungal photosensitizer.

A new tetra-α-substituted zinc(II) phthalocyanine containing dodeca-amino groups (compound 4) and its quaternized analogue (compound 5) have been prepared and evaluated for their photoactivities against Candida albicans. Compared with the dodeca-amino phthalocyanine 4, the dodeca-cationic phthalocyanine 5 exhibits a higher photodynamic inactivation against C. albicans with an IC90 value down to 1.46 μM, which can be attributed to its non-aggregated nature in aqueous environments and more efficient cellular uptake. More interestingly, 5 shows a higher photodynamic inactivation on C. albicans due to its stronger affinity to C. albicans cells than mammalian cells. These results suggest that the highly positive-charged phthalocyanine 5 is a potential non-aggregated antifungal photosensitizer, which shows some selectivity toward the fungus.

Preparation and sonodynamic activities of water-soluble tetra-α-(3-carboxyphenoxyl) zinc(II) phthalocyanine and its bovine serum albumin conjugate.

Sonodynamic therapy (SDT) is a new approach for cancer treatment, involving the synergistic effect of ultrasound and certain chemical compounds termed as sonosensitizers. A water-soluble phthalocyanine, namely tetra-α-(3-carboxyphenoxyl) zinc(II) phthalocyanine (ZnPcC4), has been prepared and characterized. The interactions between ZnPcC4 and bovine serum albumin (BSA) were also investigated by absorption and fluorescence spectroscopy. It was found that there were strong interactions between ZnPcC4 and BSA with a binding constant of 6.83×10(7)M(-1). A non-covalent BSA conjugate of ZnPcC4 (ZnPcC4-BSA) was prepared. Both ZnPcC4 and ZnPcC4-BSA exhibited efficient sonodynamic activities against HepG2 human hepatocarcinoma cells. Compared with ZnPcC4, conjugate ZnPcC4-BSA showed a higher sonodynamic activity with an IC50 value of 7.5μM. Upon illumination with ultrasound, ZnPcC4-BSA can induce an increase of intracellular reactive oxygen species (ROS) level, resulting in cellular apoptosis. The results suggest that the albumin conjugates of zinc(II) phthalocyanines functionalized with carboxyls can serve as promising sonosensitizers for sonodynamic therapy.

Synthesis and In Vitro Photodynamic Activities of an Integrin-Targeting cRGD-Conjugated Zinc(II) Phthalocyanine†

A 1,4-disubstituted zinc(II) phthalocyanine conjugated with a cyclic Arg-Gly-Asp-D-Phe-Lys (cRGDfK) moiety through a triazole linker was prepared and characterized by UV/Vis spectroscopy and high-resolution ESI-MS. The conjugate showed a relatively weak fluorescence emission in N,N-dimethylformamide (ΦF =0.08), but it was a very efficient singlet oxygen generator (ΦΔ=0.80) as a result of the di-α-substituted structure. Owing to the presence of the cyclic peptide sequence cRGDfK, which is a well-known αvβ3 -integrin antagonist, this conjugate exhibited significantly higher cellular uptake toward the αvβ3(+) U87-MG cells compared with the αvβ3(-) MCF-7 cells, as determined by flow cytometry and fluorescence microscopy. The photocytotoxicity of this compound against these two cell lines, however, was comparable owing to the similar efficiency of intracellular reactive oxygen species generation. Confocal microscopic studies also revealed that this conjugate localized preferentially in the lysosomes, but not in the nucleus, endoplasmic reticulum, and mitochondria of the U87-MG cells.

Silicon(IV) phthalocyanines substituted axially with different nucleoside moieties. Effects of nucleoside type on the photosensitizing efficiencies and in vitro photodynamic activities.

A series of new silicon(IV) phthalocyanines (SiPcs) di-substituted axially with different nucleoside moieties have been synthesized and evaluated for their singlet oxygen quantum yields (ΦΔ) and in vitro photodynamic activities. The adenosine-substituted SiPc shows a lower photosensitizing efficiency (ΦΔ=0.35) than the uridine- and cytidine-substituted analogs (ΦΔ=0.42-0.44), while the guanosine-substituted SiPc exhibits a weakest singlet oxygen generation efficiency with a ΦΔ value down to 0.03. On the other hand, replacing axial adenosines with chloro-modified adenosines and purines can result in the increase of photogenerating singlet oxygen efficiencies of SiPcs. The formed SiPcs 1 and 2, which contain monochloro-modified adenosines and dichloro-modified purines respectively, appear as efficient photosensitizers with ΦΔ of 0.42-0.44. Both compounds 1 and 2 present high photocytotoxicities against HepG2 and BGC823 cancer cells with IC50 values ranging from 9nM to 33nM. The photocytotoxicities of these two compounds are remarkably higher than the well-known anticancer photosensitizer, chlorin e6 (IC50=752nM against HepG2 cells) in the same condition. As revealed by confocal microscopy, for both cell lines, compound 1 can essentially bind to mitochondria, while compound 2 is just partially localized in mitochondria. In addition, the two compounds induce cell death of HepG2 cells likely through apoptosis.

Oligolysine-conjugated zinc(II) phthalocyanines as efficient photosensitizers for antimicrobial photodynamic therapy.

A series of zinc(II) phthalocyanines conjugated with an oligolysine chain (n=2, 4, and 8) were synthesized and characterized by using various spectroscopic methods. As shown by using UV/Vis and fluorescence spectroscopic methods, these compounds were nonaggregated in N,N-dimethylformamide, and gave a weak fluorescence emission and high singlet oxygen quantum yield (Φ(Δ) =0.86-0.89) as a result of their di-α-substitution. They became slightly aggregated in water with 0.05 % Cremophor EL, but they could still generate singlet oxygen effectively. The antimicrobial photodynamic activities of these compounds were then examined against various bacterial strains, including the Gram-positive methicillin-sensitive Staphylococcus aureus ATCC 25923 and methicillin-resistant Staphylococcus aureus ATCC BAA-43, and the Gram-negative Escherichia coli ATCC 35218 and Pseudomonas aeruginosa ATCC 27853. Generally, the dyes were much more potent toward the Gram-positive bacteria. Only 15 to 90 nM of these photosensitizers was required to induce a 4 log reduction in the cell viability of the strains. For Escherichia coli, the photocytotoxicity increased with the length of the oligolysine chain. The octalysine derivative showed the highest potency with a 4 log reduction concentration of 0.8 μM. Pseudomonas aeruginosa was most resistant to the photodynamic treatment. The potency of the tetralysine derivative toward a series of clinical strains of Staphylococcus aureus was also examined and found to be comparable with that toward the nonclinical counterparts. Moreover, the efficacy of these compounds in photodynamic inactivation of viruses was also examined. They were highly photocytotoxic against the enveloped viruses influenza A virus (H1N1) and herpes simplex virus type 1 (HSV1), but exhibited no significant cytotoxicity against the nonenveloped viruses adenovirus type 3 (Ad3) or coxsackievirus (Cox B1). The octalysine derivative also showed the highest potency with an IC(50) value of 0.05 nM for the two enveloped viruses.