Design and photophysical properties of new RGD targeted tetraphenylchlorins and porphyrins

Pyrobacteriopheophorbide-a derivatives possessing various hydrophilic esterifying groups at the C17-propionate residues for photodynamic therapy

Aiming at the application to photodynamic therapy, natural bacteriochlorophyll-a was converted to chemically stable free-base derivatives possessing different kinds of hydrophilic C17-propionate residues. These semi-synthetic bacteriochlorins were found to have self-assembling ability in an aqueous environment and formed stable J-type aggregates in a cell culture medium containing 0.2% DMSO. The electronic absorption spectra of all the sensitizers showed Qy absorption maxima at 754 nm in DMSO as their monomeric states, while a drastic shift of the red-most bands to ca. 880 nm was observed in the aqueous medium. The circular dichroism spectra in the medium showed much intense signals compared to those measured in DMSO, supporting the formation of well-ordered supramolecular structures. By introducing hydrophilic side chains, the bacteriochlorin sensitizers could be dispersed in the aqueous medium as their J-aggregates without the use of any surfactants. Cellular uptake efficiencies as well as photodynamic activities were evaluated using human cervical adenocarcinoma HeLa cells. Among the 11 photosensitizers investigated, the best result was obtained for a charged derivative possessing trimethylammonium terminal (17-CH2CH2COOCH2CH2N+(CH3)3I-) and photocytotoxicity of EC50 = 0.09 μM was achieved by far-red light illumination of 35 J/cm2 from an LED panel (730 nm).

Self-assembled porphyrin-peptide cages for photodynamic therapy

The development of photodynamic therapy requires access to smart photosensitizers which combine appropriate photophysical and biological properties. Interestingly, supramolecular and dynamic covalent chemistries have recently shown their ability to produce novel architectures and responsive systems through simple self-assembly approaches. Herein, we report the straightforward formation of porphyrin-peptide conjugates and cage compounds which feature on their surface chemical groups promoting cell uptake and specific organelle targeting. We show that they self-assemble, in aqueous media, into positively-charged nanoparticles which generate singlet oxygen upon green light irradiation, while also undergoing a chemically-controlled disassembly due to the presence of reversible covalent linkages. Finally, the biological evaluation in cells revealed that they act as effective photosensitizers and promote synergistic effects in combination with Doxorubicin.

Carbon-1 versus Carbon-3 Linkage of d-Galactose to Porphyrins: Synthesis, Uptake, and Photodynamic Efficiency

The use of glycosylated compounds is actively pursued as a therapeutic strategy for cancer due to the overexpression of various types of sugar receptors and transporters on most cancer cells. Conjugation of saccharides to photosensitizers such as porphyrins provides a promising strategy to improve the selectivity and cell uptake of the photosensitizers, enhancing the overall photosensitizing efficacy. Most porphyrin-carbohydrate conjugates are linked via the carbon-1 position of the carbohydrate because this is the most synthetically accessible approach. Previous studies suggest that carbon-1 galactose derivatives show diminished binding since the hydroxyl group in the carbon-1 position of the sugar is a hydrogen bond acceptor in the galectin-1 sugar binding site. We therefore synthesized two isomeric porphyrin-galactose conjugates using click chemistry: one linked via the carbon-1 of the galactose and one linked via carbon-3. Free base and zinc analogs of both conjugates were synthesized. We assessed the uptake and photodynamic therapeutic (PDT) activity of the two conjugates in both monolayer and spheroidal cell cultures of four different cell lines. For both the monolayer and spheroid models, we observe that the uptake of both conjugates is proportional to the protein levels of galectin-1 and the uptake is suppressed after preincubation with an excess of thiogalactose, as measured by fluorescence spectroscopy. Compared to that of the carbon-1 conjugate, the uptake of the carbon-3 conjugate was greater in cell lines containing high expression levels of galectin-1. After photodynamic activation, MTT and lactate dehydrogenase assays demonstrated that the conjugates induce phototoxicity in both monolayers and spheroids of cancer cells.

Synthesis and photophysical properties of thioglycosylated chlorins, isobacteriochlorins, and bacteriochlorins for bioimaging and diagnostics

The facile synthesis and photophysical properties of three nonhydrolyzable thioglycosylated porphyrinoids are reported. Starting from meso-perfluorophenylporphyrin, the nonhydrolyzable thioglycosylated porphyrin (PGlc₄), chlorin (CGlc₄), isobacteriochlorin (IGlc₄), and bacteriochlorin (BGlc₄) can be made in 2-3 steps. The ability to append a wide range of targeting agents onto the perfluorophenyl moieties, the chemical stability, and the ability to fine-tune the photophysical properties of the chromophores make this a suitable platform for development of biochemical tags, diagnostics, or as photodynamic therapeutic agents. Compared to the porphyrin in phosphate buffered saline, CGlc₄ has a markedly greater absorbance of red light near 650 nm and a 6-fold increase in fluorescence quantum yield, whereas IGlc₄ has broad Q-bands and a 12-fold increase in fluorescence quantum yield. BGlc₄ has a similar fluorescence quantum yield to PGlc₄ (<10%), but the lowest-energy absorption/emission peaks of BGlc₄ are considerably red-shifted to near 730 nm with a nearly 50-fold greater absorbance, which may allow this conjugate to be an effective PDT agent. The uptake of CGlc₄, IGlc₄, and BGlc₄ derivatives into cells such as human breast cancer cells MDA-MB-231 and K:Molv NIH 3T3 mouse fibroblast cells can be observed at nanomolar concentrations. Photobleaching under these conditions is minimal.

Bifunctional agents for imaging and therapy

Multiple, complementary techniques for tumor detection, including magnetic resonance, nuclear and optical imaging, are under active development; each approach has particular strengths and advantages. Efforts are also currently underway to develop bifunctional agents, so that a single molecule can be used for imaging, therapy, and monitoring the long-term tumor response. This chapter is mainly focused on illustrating the utility of certain tumor-avid photosensitizers in developing agents for tumor imaging [fluorescence, magnetic resonance imaging (MRI), positron emission tomography (PET)] and photodynamic therapy. Recent approaches for developing target-specific agents for photodynamic therapy (PDT) and in vivo tumor imaging are also briefly discussed.