Functionalization of OEP-Based Benzochlorins To Develop Carbohydrate-Conjugated Photosensitizers. Attempt To Target β-Galactoside-Recognized Proteins

Meso-Formyl, Vinyl, and Ethynyl Porphyrins-Multipotent Synthons for Obtaining a Diverse Array of Functional Derivatives

This review presents a strategy for obtaining various functional derivatives of tetrapyrrole compounds based on transformations of unsaturated carbon-oxygen and carbon-carbon bonds of the substituents at the meso position (meso-formyl, vinyl, and ethynyl porphyrins). First, synthetic approaches to the preparation of these precursors are described. Then diverse pathways for the transformations of the multipotent synthons are discussed, revealing a variety of products of such reactions. The structures, electronic, and optical properties of the compounds obtained by the methods under consideration are analyzed. In addition, there is an overview of the applications of the products obtained. Biomedical use of the compounds is among the most important. Finally, the advantages of using the reviewed synthetic strategy to obtain dyes with targeted properties are highlighted.

Impact of mono- and di-β-galactose moieties in in vitro / in vivo anticancer efficacy of pyropheophorbide-carbohydrate conjugates by photodynamic therapy

To investigate the impact of mono- and di-β-galactose moieties in tumor uptake and photodynamic therapy (PDT) efficacy, HPPH [3-(1'-hexyloxy)ethyl-3-devinylpyropheophorobide-a], the meso pyropheophorbide-a [3-ethyl-3-devinyl-pyropheophorbide-a], and the corresponding 20-benzoic acid analogs were used as starting materials. Reaction of the intermediates containing one or two carboxylic acid functionalities with 1-aminogalactose afforded the desired 17²- or 20(4')- mono- and 17², 20(4')-di galactose conjugated photosensitizers (PSs) with and without a carboxylic acid group. The overall lipophilicity caused by the presence of galactose in combination with either an ethyl or (1'-hexyloxy)ethyl side chain at position-3 of the macrocycle made a significant difference in in vitro uptake by tumor cells and photoreaction upon light exposure. Interestingly, among the PSs investigated, compared to HPPH 1 the carbohydrate conjugates 2 and 11 in which β-galactose moieties are conjugated at positions 17² and 20(4') of meso-pyro pheophorbide-a showed similar in vitro efficacy in FaDu cell lines, but in SCID mice bearing FaDu tumors (head & neck) Ps 11 gave significantly improved long-term tumor cure.

Synthesis and Photophysical Properties of Tumor-Targeted Water-Soluble BODIPY Photosensitizers for Photodynamic Therapy

The synthesis of three water-soluble lactose-modified 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based photosensitizers with tumor-targeting capabilities is reported, including an investigation into their photodynamic therapeutic activity on three distinct cancer cell lines (human hepatoma Huh7, cervical cancer HeLa, and breast cancer MCF-7 cell lines). The halogenated BODIPY dyes exhibited a decreased fluorescence quantum yield compared to their non-halogenated counterpart, and facilitated the efficient generation of singlet oxygen species. The synthesized dyes exhibited low cytotoxicities in the dark and high photodynamic therapeutic capabilities against the treated cancer cell lines following irradiation at 530 nm. Moreover, the incorporation of lactose moieties led to an enhanced cellular uptake of the BODIPY dyes. Collectively, the results presented herein provide promising insights for the development of photodynamic therapeutic agents for cancer treatment.

Study on Liposomal Encapsulation of New Bodipy Sensitizers for Photodynamic Therapy

We report a series of four efficient photosensitizers (PSs) based on a Bodipy core for photodynamic therapy (PDT). In the absence of hydrophilic functional groups, these PSs have been encapsulated in liposomes and examined for photocytotoxicity against human ovarian carcinoma cell line (SK-OV-3). The IC₅₀ values obtained are as low as 0.350 μM, which compete with the classical photosensitizer chlorine E6 (IC₅₀ = 0.39 μM) under similar experimental conditions.

Cancer cell spheroids are a better screen for the photodynamic efficiency of glycosylated photosensitizers

Photodynamic Therapy (PDT) relies on the use of non-toxic photosensitizers that are locally and selectively activated by light to induce cell death or apoptosis through reactive oxygen species generation. The conjugation of porphyrinoids with sugars that target cancer is increasingly viewed as an effective way to increase the selectivity of PDT. To date, in vitro PDT efficacy is mostly screened using two-dimensional monolayer cultures. Compared to monolayer cultures, three-dimensional spheroid cultures have unique spatial distributions of nutrients, metabolites, oxygen and signalling molecules; therefore better mimic in vivo conditions. We obtained 0.05 mm3 spheroids with four different human tumor cell lines (HCT-116, MCF-7, UM-UC-3 and HeLa) with appropriate sizes for screening PDT agents. We observed that detachment from monolayer culture and growth as tumor spheroids was accompanied by changes in glucose metabolism, endogenous ROS levels, galectin-1 and glucose transporter GLUT1 protein levels. We compared the phototoxic responses of a porphyrin conjugated with four glucose molecules (PorGlu4) in monolayer and spheroid cultures. The uptake and phototoxicity of PorGlu4 is highly dependent on the monolayer versus spheroid model used and on the different levels of GLUT1 protein expressed by these in vitro platforms. This study demonstrates that HCT-116, MCF-7, UM-UC-3 and HeLa spheroids afford a more rational platform for the screening of new glycosylated-photosensitizers compared to monolayer cultures of these cancer cells.

Targeted Nanomaterials for Phototherapy

Phototherapies involve the irradiation of target tissues with light. To further enhance selectivity and potency, numerous molecularly targeted photosensitizers and photoactive nanoparticles have been developed. Active targeting typically involves harnessing the affinity between a ligand and a cell surface receptor for improved accumulation in the targeted tissue. Targeting ligands including peptides, proteins, aptamers and small molecules have been explored for phototherapy. In this review, recent examples of targeted nanomaterials used in phototherapy are summarized.

Synthesis and photodynamic activities of a new metronidazole-appended porphyrin and its Zn(II) complex

One novel porphyrin 5,10,15-tris(phenyl)-20-[4-(2-(2-methyl-5-nitro-imidazolyl)ethoxyl)phenyl] porphyrin and its zinc(II) metalloporphyrin were synthesized and characterized by IR, UV-vis, 1H NMR, MS and elemental analysis. The single crystal structure of zinc(II) porphyrin shows that the Zn(II) ion is coordinated with four nitrogen atoms of porphyrin ring and one oxygen atom of ethanol from axial, forming a five-coordinated square pyramidal geometry. Their cytotoxicity and photodynamic activity against breast cancer cells were studied. The results indicate that both of the porphyrins display high phototoxicity to the breast cancer cells with the negligible dark toxicity. In addition, the photodynamic activity of zinc(II) porphyrin was obviously higher than that of the free porphyrin.

Synthesis and Fluorescence Properties of Metalloporphyrazines Carrying 2-(Ethyl)-1,3-Dioxanethio-Groups

The synthesis, photophysical and spectroscopic properties of soluble 2-(ethyl)-1,3-dioxanethio-substituted metal-free and metalloporphyrazines containing Mg(II), Zn(II), Co(II) and Ni(II) are reported. The aggregation behaviour of these compounds was investigated in different solvents and concentrations. The effects of the substituent and the nature of the metal ion on the photophysical parameters of the Mg(II), Zn(II), Co(II) and Ni(II) porphyrazines are also reported.

Special reactive oxygen species generation by a highly photostable BODIPY-based photosensitizer for selective photodynamic therapy

We introduce a new class of photostable, efficient photosensitizers based on boron-dipyrromethene (BODIPY) derivatives that can generate singlet oxygen and super oxide simultaneously under irradiation. For compound preparation, appropriate regulation of the reaction conditions and control of specifically substituted BODIPY derivatives have been achieved. After biologically evaluating the intracellular uptake, localization, and phototoxicity of the compounds, we conclude that 3,5-dianiline-substituted BODIPY is a potentially selective photodynamic therapy candidate because its photodamage is more efficient in cancer cells than in normal cells, without apparent dark toxicity. Furthermore, direct comparison of photodamage efficacy revealed that our compound has better efficacy than Foscan and nearly equal efficacy to that of methylene blue.

Synthesis of three novel imidazolyl-appended porphyrins and their cytostatic and phototoxic activity on A431 cells

Three imidazolyl-appended porphyrins were synthesized and characterized by 1 H NMR, elemental analyses, MS and UV-vis spectra. Anticancer activities of porphyrins have been evaluated against cutaneous squamous cell carcinoma (A431 cells) in vitro. The results indicate that the porphyrins have high selective cytotoxicity towards A431 cells in the absence of light and improved phototoxic activity upon exposure to UV light. The yield of singlet oxygen generated by porphyrins were also evaluated by measuring the absorption decay of 1,3-diphenylisobenzofuran (DPBF) in DMF. The phototoxicities of porphyrins against A431 cells were enhanced along with the increase of singlet oxygen.

Boron-Fluorine Photosensitizers for Photodynamic Therapy

Photodynamic therapy (PDT) has been recognized as a promising treatment for cancers and tumors, in which photosensitizer is one of the most important issues. As a class of excellent fluorescent dyes, boron-fluorine derivatives (typically 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, BODIPY) have preferable ability of generating singlet oxygen and have been under extensive study for PDT sensitizers. In this review, we summarize the recent progress of design and applications of boron-fluorine-based photosensitizers for PDT.

Synthesis and photodynamic properties of maltohexaose-conjugated porphyrins

A series of porphyrin derivatives with one to four maltohexaose moieties in their meso positions have been synthesized. Zinc or free-base m-THPP (5,10,15,20-tetrakis(m-hydroxyphenyl)-porphyrin) was used as the porphyrin platform. The reaction of m-THPP with 3-iodopropyl nonadecaacetylmaltohexaoside afforded a mixture of all possible combinations of glycoconjugated porphyrins having one to four maltohexaose moieties; monoglycosylated (Ac-1), bisglycosylated (Ac-cis-2 and Ac-trans-2), triglycosylated (Ac-3), and tetraglycosylated (Ac-4) porphyrins were obtained in 11–26% yield. Removal of acetyl groups at maltohexaose moiety afforded highly water-soluble glycoconjugated porphyrins 1–4. Zinc derivatives were synthesized in a similar manner. These maltohexaose-linked porphyrins exhibit remarkable water-solublity (530 mg/mL for 4). The singlet oxygen production ability upon visible light irradiation is not affected by the maltohexaose substitution. Photo- and dark cytotoxicities of the maltohexaose-conjugated porphyrins 1–4 and Zn-1–4 were examined against a HeLa cell line, which showed that the mono-maltohexaosylated derivative (1 and Zn-1) was the most effective photosensitizer for PDT.

"Click chemistry" in the synthesis of the first glycoconjugates of bacteriochlorin series

A regioselective synthesis of glycoconjugates based on bacteriochlorophyll a and lactose derivatives has been carried out. The conjugation was achieved via 1,3-dipolar cycloaddition of bacteriochlorins containing a terminal triple bond and a lactose azide derivative. The conjugates obtained in this way had one or two disaccharide fragments attached to pyrrol A, the exocyclic imide ring of the tetrapyrrolyc macrocycle, or to both positions. Exhaustive NMR analysis by 1D and 2D NMR experiments ( 1H-1H COSY, TOCSY, ROESY, 1H-13C HSQC, HMBC, and 1H-15N HMBC) allowed us to determine the structures and configurations of the glycoconjugates obtained. A bioassay of the glycoconjugates using the Hep2 cell line showed that the highest efficiency was observed for the glycosylated bacteriopurpurinimide containing a lactose residue at pyrrole ring A.

[Interfacial behaviour of glycoconjugated tetraphenylporphyrins and their interaction with biomimetic models of the cell membrane]

INTRODUCTION

Porphyrins are photosensitizers usable in photodynamic therapy. Although these molecules are clinically effective, their low water solubility and their lack of specificity are major drawbacks to their development. Our study was aimed at analysing the interfacial behaviour of glycoconjugated tetraphenylporphyrins newly synthesized at the Curie Institute, and their interaction with model membranes bearing a specific lectin mimicking a mannose membrane receptor in retinoblastoma.

MATERIAL AND METHODS

The interfacial behaviour of the porphyrins was analysed by surface pressure measurements, and their specific interaction with the lectin, by dynamic light scattering (liposomes) and the quartz crystal microbalance technique (supported bilayers).

RESULTS

All porphyrin derivatives were able to organize at the air/liquid interface. The dendrimeric compounds formed more stable monolayers than the others, and generally showed good mixing properties with the phospholipid used for liposome preparation. In the presence of concanavalin A, the porphyrin bearing-liposomes behaved differently depending on the nature (mannosylated or not) of the porphyrins.

DISCUSSION

The interfacial behaviour of the tetraphenylporphyrins is directly related to the orientation of the tetrapyrrolic macrocycle controlled by the grafted groups. Incorporated into a liposome bilayer, glycodendrimeric porphyrins expose their sugar moieties at the vesicle surface. The spacer length plays a crucial role by increasing sugars freedom and enhancing glycosylated liposomes interaction with the lectin.

CONCLUSION

Compared to the other studied compounds, the glycodendrimeric porphyrins seem very promising compounds and are now evaluated on cell cultures.

Synthetic transformations of porphyrins – Advances 2002-2004

Contemporary methods for the modification of porphyrins are presented. In association with the Third International Conference on Porphyrins and Phthalocyanines (ICPP-3) a survey of current method developments and reactivity studies is made. The review focuses on synthetic transformations of porphyrins currently in use for various applications and on functional group transformations. A brief survey of important developments covers selectively the literature from late 2001 to early 2004.

Synthesis and characterization of 1,8(11),15(18),22(25)-tetraglycosylated zinc(II) phthalocyanines

In continuation of our work on glycosylated phthalocyanines, a new series of 1,8(11),15(18),22(25)-tetraglycosylated zinc(II) phthalocyanines (PcZns) have been synthesized and characterized. 3-glycosylated phthalonitriles were synthesized through nitrite displacement in 3-nitrophthalonitrile with anomerically deprotected glycoses. The anomerically glycosylated phthalonitriles were then treated with hexamethyldisilazane (HMDS), trimethylsilyltriflate (TMSOTf) and zinc salt in DMF to form the corresponding acetyl-protected PcZns, followed by deprotection of acetyl groups by NaOMe in methanol/DMSO mixture. The formed unprotected tetraglycosylated PcZns are highly soluble in water, which is a necessary condition for potential biological applications.

Synthesis and photophysics of an octathioglycosylated zinc(II) phthalocyanine

A water soluble zinc(II) phthalocyanine symmetrically appended with eight thioglucose units was synthesized from commercially available hexadecafluorophthalocyaninatozinc(II) by controlled nucleophilic substitution of the peripheral fluoro groups. The photophysical properties and cancer cell uptake studies of this nonhydrolyzable thioglycosylated phthalocyanine are reported. The new compound has amphiphilic character, is chemically stable, and can potentially be used as a photosensitizer in photodynamic therapy.

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.

Porphyrin and galactosyl conjugated micelles for targeting photodynamic therapy

PURPOSE

To study the targeting and photodynamic therapy efficiency of porphyrin and galactosyl conjugated micelles based on amphiphilic copolymer galactosyl and mono-aminoporphyrin (APP) incoporated poly(2-aminoethyl methacrylate)-polycaprolactone (Gal-APP-PAEMA-PCL).

METHODS

Poly(2-aminoethyl methacrylate)-polycaprolactone (PAEMA-PCL) was synthesized by the combination of ring opening polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization, and then Gal-APP-PAEMA-PCL was obtained after conjugation of lactobionic acid and 5-(4-aminophenyl)-10,15,20-triphenylporphyrin (APP) to PAEMA-PCL. The chemical structures of the copolymers were characterized, and their biological properties were evaluated in human laryngeal carcinoma (HEp2) and human hepatocellular liver carcinoma (HepG2) cells.

RESULTS

Both APP-PAEMA-PCL and Gal-APP-PAEMA-PCL did not exhibit dark cytotoxicity to HEp2 cells and HepG2 cells. However, Gal-APP-PAEMA-PCL was taken up selectively by HepG2 cells and had the higher phototoxicity effect. Both polymers preferentially localized within cellular vesicles that correlated to the lysosomes.

CONCLUSIONS

The results indicated that porphyrin and galactosyl conjugated polymer micelles exhibited higher targeting and photodynamic therapy efficacy in HepG2 cells than in HEp2 cells.

Conjugation of 2-(1'-hexyloxyethyl)-2-devinylpyropheophorbide-a (HPPH) to carbohydrates changes its subcellular distribution and enhances photodynamic activity in vivo

The carbohydrate moieties on conjugating with 3-(1'-hexyloxyethyl)-3-devinyl pyropeophorbide-a (HPPH) altered the uptake and intracellular localization from mitochondria to lysosomes. In vitro, HPPH-Gal 9 PDT showed increased PDT efficacy over HPPH-PDT as detectable by the oxidative cross-linking of nonphosphorylated STAT3 and cell killing in ABCG2-expressing RIF cells but not in ABCG2-negative Colon26 cells. This increased efficacy in RIF cells could at least partially be attributed to increased cellular accumulation of 9, suggesting a role of the ABCG2 transporter for which HPPH is a substrate. While such differences in the accumulation in HPPH derivatives by tumor tissue in vivo were not detectable, 9 still showed an elevated light dose-dependent activity compared to HPPH in mice bearing RIF as well as Colon26 tumors. Further optimization of the carbohydrate conjugates at variable treatment parameters in vivo is currently underway.

Comparative positron-emission tomography (PET) imaging and phototherapeutic potential of 124I- labeled methyl- 3-(1'-iodobenzyloxyethyl)pyropheophorbide-a vs the corresponding glucose and galactose conjugates

In our present study, 3-(1(')-m-iodobenzyloxyethyl)pyropheophorbide-a methyl ester 1, 3-(1'-m-iodobenzyloxyethyl)-17(2)-{(2-deoxy)glucose}pyropheophorbide-a 2, and 3-(1'-m-iodobenzyloxyethyl)-17(2)-{(1-deoxy)galactose}pyropheophorbide-a 3 were synthesized and converted into the corresponding (124)I-labeled analogues by reacting the intermediate trimethyltin analogues with Na(124)I. Photosensitizers 1-3 were evaluated for the PDT efficacy in C3H mice bearing RIF tumors at variable doses and showed a significant long-term tumor cure. Among the compounds investigated, the non-carbohydrate analogue 1 was most effective. These results were in contrast to the in vitro data, where compared to the parent analogue the corresponding galactose and glucose derivatives showed enhanced cell kill. Among the corresponding (124)I-labeled analogues, excellent tumor images were obtained from compound 1 in both tumor models (RIF and Colon-26) and the best tumor contrast was observed at 72 h after injection. Conjugating a glucose moiety to photosensitizer 1 initially diminished its tumor uptake, whereas with time the corresponding galactose analogue showed improved tumor contrast.

Sugar-dependent photodynamic effect of glycoconjugated porphyrins: A study on photocytotoxicity, photophysical properties and binding behavior to bovine serum albumin (BSA)

The photocytotoxicity of four glycoconjugated porphyrins, namely 5,10,15,20-tetrakis[4-(beta-D-glucopyranosyloxy)phenyl]porphyrin (p-1a), 5,10,15,20-tetrakis[4-(beta-D-galactopyranosyloxy)phenyl]porphyrin (p-1b), 5,10,15,20-tetrakis[4-(beta-D-xylopyranosyloxy)phenyl]porphyrin (p-1c) and 5,10,15,20-tetrakis[4-(beta-D-arabinopyranosyloxy)phenyl]porphyrin (p-1d), was evaluated in HeLa cells in the concentration range from 1 to 7 microM using a light dose of 16 J x cm(-2) with a wavelength greater than 500 nm. The photocytotoxicity depends on the sugar moieties, and increases in the order of p-1d<p-1a<p-1b<p-1c. The order of the photocytotoxicity is at variance with that of the cellular uptake reported previously. On the other hand, the photophysical properties of the glycoconjugated porphyrins also depends on the sugar moieties in physiological media such as phosphate buffered saline (PBS) containing 10 wt.% bovine serum albumin (BSA). In particular, the oscillator strength in the range above 500 nm increases in the order of p-1d=p-1a<p-1c<p-1b, which is good agreement with the order of the photocytotoxicity in HeLa cells. The interaction between the glycoconjugated porphyrins and BSA was evaluated by means of electronic absorption, fluorometric and circular dichroic (CD) titrations. Fluorometric titration showed no differences in the apparent binding constants, K, between the glycoconjugated porphyrins p-1a, p-1b, p-1c and p-1d. On the other hand, the number of binding sites, n, depends on the sugar moieties of the glycoconjugated porphyrin, and increases in the order of p-1b<p-1a<p-1d<p-1c. CD titration was also characterized by the n value determined by fluorometric titration, suggesting the n value is a good descriptor for the interaction between glycoconjugated porphyrins and BSA. However, it was found that the n value was poorly related to the photophysical properties in physiological media and the photocytotoxicity. Even though the role of the sugar moieties on the photodynamic effect is not fully understood, the photophysical properties of the glycoconjugated porphyrins are strongly modulated by the physiological media resulting in the sugar-dependent photocytotoxicity.

Synthesis and cellular studies of PEG-functionalized meso-tetraphenylporphyrins

The total syntheses of four PEG-functionalized porphyrins, containing one to four low molecular weight PEG chains linked via amide bonds to the para-phenyl positions of meso-tetraphenylporphyrin, are reported. The hydrophobic character of the PEG-porphyrins decreases with the number of PEG chains linked to the porphyrin ring, while their tendency for aggregation in buffered aqueous solution increases. The porphyrins containing one or two PEG chains accumulated within human HEp2 cells to a much higher extent than those having three or four PEGs at the macrocycle periphery. All PEG-porphyrins were found to be non-toxic in the dark, and only those containing one or two PEG chains were phototoxic (IC(50)=2 microM at 1J/cm(2) light dose). The preferential sites of subcellular localization of the porphyrins containing one or two PEG chains were found to be the mitochondria and endoplasmic reticulum (ER), while those containing three or four PEG chains localize preferentially in the lysosomes.

Glycosyl bis-porphyrin conjugates: Synthesis and potential application in PDT

Syntheses of new glycosylated neutral and cationic porphyrin dimers linked at the meso-position via a flexible hydrocarbon chain are described. A detailed 1H and 13C NMR study allows their complete structural elucidation. The UV-visible, fluorescence and MALDI mass spectra are also presented. Photocytotoxicities of these compounds against K562 leukaemia cell line are compared to those of Photofrin II.