Maltotriose-Chlorin e6 Conjugate Linked via Tetraethyleneglycol as an Advanced Photosensitizer for Photodynamic Therapy. Synthesis and Antitumor Activities against Canine and Mouse Mammary Carcinoma Cells

Glycoconjugated chlorins represent a promising class of compounds that meet the requirements for the third-generation photosensitizer (PS) for photodynamic therapy (PDT). We have focused on the use of glucose (Glc) to improve the performance of the PS based on the Warburg effect-a phenomenon where tumors consume higher Glc levels than normal cells. However, as a matter of fact, Glc-conjugation has a poor efficacy in hydrophilic modification; thus, the resultant PS is not suitable for intravenous injection. In this study, a Glc-based oligosaccharide, such as maltotriose (Mal₃), is conjugated to chlorin e6 (Ce6). The conjugation is assisted by two additional molecular tools, such as propargyl amine and a tetraethylene glycol (TEG) derivative. This route produced the target Mal₃-Ce6 conjugate linked via the TEG spacer (Mal₃-TEG-Ce6), which shows the required photoabsorption properties in the physiological media. The PDT test using canine mammary carcinoma (SNP) cells suggested that the antitumor activity of Mal₃-TEG-Ce6 is extremely high. Furthermore, in vitro tests against mouse mammary carcinoma (EMT6) cells have been demonstrated, providing insights into the photocytotoxicity, subcellular localization, and analysis of cell death and reactive oxygen species (ROS) generation for the PDT system with Mal₃-TEG-Ce6. Both apoptosis and necrosis of the EMT6 cells occur by ROS that is generated via the photochemical reaction between Mal₃-TEG-Ce6 and molecular oxygen. Consequently, Mal₃-TEG-Ce6 is shown to be a PS showing the currently desired properties.

Synthesis of Water-Soluble Thioglycosylated trans-A2B2 Type Porphyrins: Cellular Uptake Studies and Photodynamic Efficiency

The synthesis of water-soluble thioglycosylated A₂B₂ type porphyrins and their zinc(II) complexes is reported. The water-soluble trans-A₂B₂ porphyrins were synthesized in two steps, via [2+2] condensation between thioglycosylated dipyrromethanes and aromatic aldehydes in 15-21% yields. The thioglycosylated trans-A₂B₂ porphyrins showed decent in vitro singlet oxygen generation, which was supported by the intracellular DCFDA study. The in vitro cellular investigations of thioglycosylated A₂B₂ porphyrins were carried out in lung cancer cells (A549) to test their photodynamic therapeutic (PDT) activity. The PDT study revealed significant cytotoxicities of porphyrins with IC₅₀ values between 23.3 and 44.2 μM in the dark, whereas, after visible light exposure, the photosensitizers exhibited IC₅₀ values around 11.1-23.8 μM. The water-soluble thioglycosylated zinc(II) porphyrins having two meso-N-butylcarbazole groups exhibited an excellent degree of photocytotoxicity (IC₅₀ = 4.6-8.8 μM). The flow cytometry analysis revealed that cellular uptake and ROS (reactive oxygen species) generation efficiency of water-soluble thioglycosylated zinc(II) porphyrins were considerably higher than nonmetalated porphyrins. Confocal microscopy images displayed substantial distribution in the endoplasmic reticulum with partial colocalization in mitochondria and lysosomes of water-soluble thioglycosylated zinc(II) porphyrins in A549 cells.

Nucleophilic Thioglycosylation of Pentafluorophenyl-Substituted Porphyrinoids: Synthesis of Glycosylated Calix[n]phyrin and [28]Hexaphyrin Systems

The use of carbohydrate thiolates for facile, high-yielding, regio- and stereoselective nucleophilic substitution reactions of complex pentafluorophenyl-substituted porphyrinoids is reported. The title reaction has successfully been applied to calix[4]phyrin, calix[6]phyrin, and [28]hexaphyrin substrates. The novel glycoporphyrinoid products with their extraordinary structures and unique photophysical properties are soluble in aqueous solutions and can serve as platforms for applications in biomedicine, catalysis, coordination, or redox chemistry.

Maltotriose-conjugation to a fluorinated chlorin derivative generating a PDT photosensitizer with improved water-solubility

A chlorin derivative was encircled with four maltotriose (Mal₃) molecules to produce an oligosaccharide-conjugate meeting the requirements of a third generation photodynamic therapy (PDT) photosensitizer.

Photophysics of glycosylated derivatives of a chlorin, isobacteriochlorin and bacteriochlorin for photodynamic theragnostics: discovery of a two-photon-absorbing photosensitizer

The photophysical properties of a chlorin, isobacteriochlorin and bacteriochlorin built on a core tetrapentafluorophenylporphyrin (TPPF20 ) and the nonhydrolyzable para thioglycosylated conjugates of these chromophores are presented. The photophysical characterization of these compounds was done in three different solvents to correlate with different environments in cells and tissues. Compared with TPPF20 other dyes have greater absorption in the red region of the visible spectrum and greater fluorescence quantum yields. The excited state lifetimes are from 3 to 11 ns. The radiative and nonradiative rate constants for deactivation of the excited state were estimated from the fluorescence quantum yield and excited state lifetime. The data indicate that the bacteriochlorin has strong absorption bands near 730 nm and efficiently enters the triplet manifold. The isobacteriochlorin has a 40-70% fluorescence quantum yield depending on solvent, so it may be a good fluorescent tag. The isobacteriochlorins also display enhanced two-photon absorption, thereby allowing the use of 860 nm light to excite the compound. While the two-photon cross section of 25 GM units is not large, excitation of low chromophore concentrations can induce apoptosis. The glycosylated compounds accumulate in cancer cells and a head and neck squamous carcinoma xenograft tumor model in mice. These compounds are robust to photobleaching.

Tumor targeting in photodynamic therapy. From glycoconjugated photosensitizers to glycodendrimeric one. Concept, design and properties

In this paper, we discuss the evolution over the last 15 years in the Curie Institute of the concept, the development of the design and some properties of glycoconjugated photosensitizers with the aim to optimize the tumor targeting in photodynamic therapy. By this research, we have shown that specific interactions between a mannose-lectin and trimannosylglycodendrimeric porphyrins contributed to a larger extent than non-specific ones to the overall interaction of a glycosylated tetraarylporphyrin with a membrane. The studies of in vitro photocytotoxicity showed the relevance of the global geometry of the photosensitizer, the number and position of the linked glycopyranosyl groups on the chromophore and their lipophilicity. The two best compounds appeared to be porphyrins bearing three α-glycosyl groups on para-position of meso-phenyl via a flexible linker. Compound bearing α-manosyl moieties was evaluated successfully in two in vivo xenografted animal models of human retinoblastoma and colorectal cancers. Conversely, the presence on the chromophore of three sugars via a glycodendrimeric moiety induced a potential cluster effect, but decreased the in vitro photoefficiency despite a good affinity for a mannose-lectin.

Design, synthesis and biological evaluation of folate-porphyrin: a new photosensitizer for targeted photodynamic therapy

A novel folate-porphyrin conjugate 1 for targeted photodynamic therapy of tumor was designed and synthesized. The results of fluorescence spectroscopy and confocal laser scanning microscope demonstrated that the cellular uptake of conjugate 1 by HeLa cells was 35 times higher than that of precursor porphyrin 3 after 24 h incubation, and that the presence of excessive free folic acid inhibited the cellular uptake of conjugate 1. Cytotoxicity against folate-receptor positive HeLa cells in vitro measured by MTT assay demonstrated that conjugate 1 exhibited much lower dark cytotoxicity but significant photocytotoxicity, with 86.4% of cell growth inhibition ratio after irradiation. However, conjugate 1 induced lower photocytotoxicity for normal cells and folate-receptor negative cells. These results suggest that folate-porphyrin like photosensitizers could induce a potentially useful targeted photodynamic therapy modality for folate-receptor-positive cancer cells due to the folate-receptor mediated endocytosis.

Calculation and prediction of rate and equilibrium constants for aggregation of porphyrin by molecular dynamics, Docking and QSPR methods

The aggregation of 85 porphyrin derivatives and a report on a kinetic and thermodynamic study of such aggregation behavior on varying the derivatives of porphyrin was carried out using molecular dynamics simulation and Docking. Distance diagrams of simulated compounds were obtained and decrease of curves is a clear evidence of the aggregation. Aggregation rates were studied by origin software. In order to calculate interaction energies of derivatives, compounds were docked and the equilibrium constant of porphyrin-porphyrin interaction were obtained. Quantitative Structure-Property Relationship (QSPR) studies were performed for the sets of 85 Porphyrin derivatives. Multiple Linear Regression method (MLR) and Principal Component Analysis (PCA) were used and resulted in useful models with good prediction ability. This models were able to predict the kinetic and equilibrium constant for all sets of our compounds. The correlation coefficients for prediction of rate and logarithm of equilibrium constants were 0.67 and 0.97 by MLR method respectively and 0.90 for prediction of equilibrium constant by PCA analyses. In order to have a better prediction, compounds were divided into two groups, oxygenated and non-oxygenated group and correlation coefficient for prediction of rate constants of them were obtained 0.89 and 0.94 by MLR model respectively. Results of structure-property relationship showed that, larger, more hydrophobe and more planner derivatives have higher aggregation rate.

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.

Convenient Approach to Access Octa-Glycosylated Porphyrins via “Click Chemistry”

Easy, quantitative, and one-pot introduction of eight β-lactoside-modules onto a porphyrin-core was achieved through Cu+-catalyzed chemoselective coupling (click chemistry) between a porphyrin carrying eight alkyne-terminals and β-lactosyl azides. The obtained porphyrin-based glycocluster shows not only good water-solubility but also strong/specific lectin-affinity.

Designing photosensitizers for photodynamic therapy: strategies, challenges and promising developments

Photodynamic therapy (PDT) and photodynamic antimicrobial chemotherapy (PACT) are techniques that combine the effects of visible light irradiation with subsequent biochemical events that arise from the presence of a photosensitizing drug (possessing no dark toxicity) to cause destruction of selected cells. Despite its still widespread clinical use, Photofrin® has several drawbacks that limit its general clinical use. Consequently, there has been extensive research into the design of improved alternative photosensitizers aimed at overcoming these drawbacks. While there are many review articles on the subject of PDT and PACT, these have focused on the photosensitizers that have been used clinically, with little emphasis placed on how the chemical aspects of the molecule can affect their efficacy as PDT agents. Indeed, many of the PDT/PACT agents used clinically may not even be the most appropriate within a given class. As such, this review aims to provide a better understanding of the factors that have been investigated, while aiming at improving the efficacy of a molecule intended to be used as a photosensitizer. Recent publications, spanning the last 5 years, concerning the design, synthesis and clinical usage of photosensitizers for application in PDT and PACT are reviewed, including 5-aminolevulinic acid, porphyrins, chlorins, bacteriochlorins, texaphyrins, phthalocyanines and porphycenes. It has been shown that there are many important considerations when designing a potential PDT/PACT agent, including the influence of added groups on the lipophilicity of the molecule, the positioning and nature of these added groups within the molecule, the presence of a central metal ion and the number of charges that the molecule possesses. The extensive ongoing research within the field has led to the identification of a number of potential lead molecules for application in PDT/PACT. The development of the second-generation photosensitizers, possessing shorter periods of photosensitization, longer activation wavelengths and greater selectivity for diseased tissue provides hope for attaining the ideal photosensitizer that may help PDT and PACT move from laboratory investigation to clinical practice.